Degradable quantum channels are an important class of completely positive trace-preserving maps. Among other properties, they offer a single-letter formula for the quantum and the private classical capacity and are characterized by the fact that a complementary channel can be obtained from the channel by applying a degrading channel. In this paper, we introduce the concept of approximate degradable channels, which satisfy this condition up to some finite epsilon {\textgreater}= 0. That is, there exists a degrading channel which upon composition with the channel is e-close in the diamond norm to the complementary channel. We show that for any fixed channel the smallest such e can be efficiently determined via a semidefinite program. Moreover, these approximate degradable channels also approximately inherit all other properties of degradable channels. As an application, we derive improved upper bounds to the quantum and private classical capacity for certain channels of interest in quantum communication.

}, issn = {0018-9448}, doi = {10.1109/TIT.2017.2754268}, author = {Sutter, David and Scholz, Volkher B. and Winter, Andreas and Renner, Renato} } @article {erker_autonomous_2017, title = {Autonomous Quantum Clocks: Does Thermodynamics Limit Our Ability to Measure Time?}, journal = {Physical Review X}, volume = {7}, number = {3}, year = {2017}, pages = {031022}, abstract = {Time remains one of the least well-understood concepts in physics, most notably in quantum mechanics. A central goal is to find the fundamental limits of measuring time. One of the main obstacles is the fact that time is not an observable and thus has to be measured indirectly. Here, we explore these questions by introducing a model of time measurements that is complete and autonomous. Specifically, our autonomous quantum clock consists of a system out of thermal equilibrium{\textemdash}a prerequisite for any system to function as a clock{\textemdash}powered by minimal resources, namely, two thermal baths at different temperatures. Through a detailed analysis of this specific clock model, we find that the laws of thermodynamics dictate a trade-off between the amount of dissipated heat and the clock{\textquoteright}s performance in terms of its accuracy and resolution. Our results furthermore imply that a fundamental entropy production is associated with the operation of any autonomous quantum clock, assuming that quantum machines cannot achieve perfect efficiency at finite power. More generally, autonomous clocks provide a natural framework for the exploration of fundamental questions about time in quantum theory and beyond.

}, doi = {10.1103/PhysRevX.7.031022}, url = {https://link.aps.org/doi/10.1103/PhysRevX.7.031022}, author = {Erker, Paul and Mitchison, Mark T. and Silva, Ralph and Woods, Mischa P. and Brunner, Nicolas and Huber, Marcus} } @article {nakata_decoupling_2017, title = {Decoupling with random diagonal unitaries}, journal = {Quantum}, volume = {1}, year = {2017}, month = {jul}, pages = {18}, abstract = {Yoshifumi Nakata, Christoph Hirche, Ciara Morgan, and Andreas Winter, Quantum 1, 18 (2017). https://doi.org/10.22331/q-2017-07-21-18 We investigate decoupling, one of the most important primitives in quantum Shannon theory, by replacing the uniformly distributed random unitaries commonly used to achieve the protocol, with{\textellipsis}}, doi = {10.22331/q-2017-07-21-18}, url = {https://quantum-journal.org/papers/q-2017-07-21-18/}, author = {Nakata, Yoshifumi and Hirche, Christoph and Morgan, Ciara and Winter, Andreas} } @article {818, title = {Discrimination Power of a Quantum Detector}, journal = {Physical Review Letters}, volume = {118}, year = {2017}, month = {Jan-04-2017}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.118.160502}, url = {http://link.aps.org/doi/10.1103/PhysRevLett.118.160502http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevLett.118.160502/fulltexthttp://link.aps.org/article/10.1103/PhysRevLett.118.160502}, author = {Hirche, Christoph and Hayashi, Masahito and Bagan, Emilio and Calsamiglia, John} } @article {nakata_efficient_2017, title = {Efficient Quantum Pseudorandomness with Nearly Time-Independent Hamiltonian Dynamics}, journal = {PHYSICAL REVIEW X}, volume = {7}, number = {2}, year = {2017}, month = {apr}, abstract = {Quantum randomness is an essential key to understanding the dynamics of complex many-body systems and also a powerful tool for quantum engineering. However, exact realizations of quantum randomness take an extremely long time and are infeasible in many-body systems, leading to the notion of quantum pseudorandomness, also known as unitary designs. Here, to explore microscopic dynamics of generating quantum pseudorandomness in many-body systems, we provide new efficient constructions of unitary designs and propose a design Hamiltonian, a random Hamiltonian of which dynamics always forms a unitary design after a threshold time. The new constructions are based on the alternate applications of random potentials in the generalized position and momentum spaces, and we provide explicit quantum circuits generating quantum pseudorandomness significantly more efficient than previous ones. We then provide a design Hamiltonian in disordered systems with periodically changing spin-glass-type interactions. The design Hamiltonian generates quantum pseudorandomness in a constant time even in the system composed of a large number of spins. We also point out the close relationship between the design Hamiltonian and quantum chaos.

}, issn = {2160-3308}, doi = {10.1103/PhysRevX.7.021006}, author = {Nakata, Yoshifumi and Hirche, Christoph and Koashi, Masato and Winter, Andreas} } @article {correa_enhancement_2017, title = {Enhancement of low-temperature thermometry by strong coupling}, journal = {PHYSICAL REVIEW A}, volume = {96}, number = {6}, year = {2017}, abstract = {We consider the problem of estimating the temperature T of a very cold equilibrium sample. The temperature estimates are drawn from measurements performed on a quantum Brownian probe strongly coupled to it. We model this scenario by resorting to the canonical Caldeira-Leggett Hamiltonian and find analytically the exact stationary state of the probe for arbitrary coupling strength. In general, the probe does not reach thermal equilibrium with the sample, due to their nonperturbative interaction. We argue that this is advantageous for low-temperature thermometry, as we show in our model that (i) the thermometric precision at low T can be significantly enhanced by strengthening the probe-sampling coupling, (ii) the variance of a suitable quadrature of our Brownian thermometer can yield temperature estimates with nearly minimal statistical uncertainty, and (iii) the spectral density of the probe-sample coupling may be engineered to further improve thermometric performance. These observations may find applications in practical nanoscale thermometry at low temperatures-a regime which is particularly relevant to quantum technologies.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.96.062103}, author = {Correa, Luis A. and Perarnau-Llobet, Marti and Hovhannisyan, Karen V. and Hernandez-Santana, Senaida and Mehboudi, Mohammad and Sanpera, Anna} } @article {804, title = {Entanglement and nonlocality in diagonal symmetric states of}, journal = {Physical Review A}, volume = {95}, year = {2017}, month = {Jan-04-2017}, issn = {2469-9926}, doi = {10.1103/PhysRevA.95.042128}, url = {http://link.aps.org/doi/10.1103/PhysRevA.95.042128http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevA.95.042128/fulltexthttp://link.aps.org/article/10.1103/PhysRevA.95.042128}, author = {Quesada, Ruben and Rana, Swapan and Sanpera, Anna} } @article {garcia-pintos_equilibration_2017, title = {Equilibration Time Scales of Physically Relevant Observables}, journal = {PHYSICAL REVIEW X}, volume = {7}, number = {3}, year = {2017}, abstract = {We address the problem of understanding, from first principles, the conditions under which a quantum system equilibrates rapidly with respect to a concrete observable. On the one hand, previously known general upper bounds on the time scales of equilibration were unrealistically long, with times scaling linearly with the dimension of the Hilbert space. These bounds proved to be tight since particular constructions of observables scaling in this way were found. On the other hand, the computed equilibration time scales for certain classes of typical measurements, or under the evolution of typical Hamiltonians, are unrealistically short. However, most physically relevant situations fall outside these two classes. In this paper, we provide a new upper bound on the equilibration time scales which, under some physically reasonable conditions, give much more realistic results than previously known. In particular, we apply this result to the paradigmatic case of a system interacting with a thermal bath, where we obtain an upper bound for the equilibration time scale independent of the size of the bath. In this way, we find general conditions that single out observables with realistic equilibration times within a physically relevant setup.

}, issn = {2160-3308}, doi = {10.1103/PhysRevX.7.031027}, author = {Garcia-Pintos, Luis Pedro and Linden, Noah and Malabarba, Artur S. L. and Short, Anthony J. and Winter, Andreas} } @article {891, title = {Erratum: Resource theory of coherence: Beyond states [Phys. Rev. AThe detection of change points is a pivotal task in statistical analysis. In the quantum realm, it is a new primitive where one aims at identifying the point where a source that supposedly prepares a sequence of particles in identical quantum states starts preparing a mutated one. We obtain the optimal procedure to identify the change point with certainty-naturally at the price of having a certain probability of getting an inconclusive answer. We obtain the analytical form of the optimal probability of successful identification for any length of the particle sequence. We show that the conditional success probabilities of identifying each possible change point show an unexpected oscillatory behavior. We also discuss local (online) protocols and compare them with the optimal procedure.

}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.119.140506}, author = {Sent{\'\i}s, Gael and Calsamiglia, John and Mu{\~n}oz-Tapia, Ramon} } @article {friis_flexible_2017, title = {Flexible resources for quantum metrology}, journal = {New Journal of Physics}, volume = {19}, number = {6}, year = {2017}, pages = {063044}, abstract = {Quantum metrology offers a quadratic advantage over classical approaches to parameter estimation problems by utilising entanglement and nonclassicality. However, the hurdle of actually implementing the necessary quantum probe states and measurements, which vary drastically for different metrological scenarios, is usually not taken into account. We show that for a wide range of tasks in metrology, 2D cluster states (a particular family of states useful for measurement-based quantum computation) can serve as flexible resources that allow one to efficiently prepare any required state for sensing, and perform appropriate (entangled) measurements using only single qubit operations. Crucially, the overhead in the number of qubits is less than quadratic, thus preserving the quantum scaling advantage. This is ensured by using a compression to a logarithmically sized space that contains all relevant information for sensing. We specifically demonstrate how our method can be used to obtain optimal scaling for phase and frequency estimation in local estimation problems, as well as for the Bayesian equivalents with Gaussian priors of varying widths. Furthermore, we show that in the paradigmatic case of local phase estimation 1D cluster states are sufficient for optimal state preparation and measurement.}, issn = {1367-2630}, doi = {10.1088/1367-2630/aa7144}, url = {http://stacks.iop.org/1367-2630/19/i=6/a=063044}, author = {Friis, Nicolai and Orsucci, Davide and Skotiniotis, Michalis and Sekatski, Pavel and Dunjko, Vedran and Briegel, Hans J. and D{\"u}r, Wolfgang} } @article {892, title = {From Log-Determinant Inequalities to Gaussian Entanglement via Recoverability Theory}, journal = {IEEE Transactions on Information Theory}, volume = {63}, year = {2017}, month = {Jan-11-2017}, pages = {7553 - 7568}, issn = {0018-9448}, doi = {10.1109/TIT.2017.2737546}, url = {http://ieeexplore.ieee.org/document/8004445/http://xplorestaging.ieee.org/ielx7/18/8071168/08004445.pdf?arnumber=8004445}, author = {Lami, Ludovico and Hirche, Christoph and Adesso, Gerardo and Winter, Andreas} } @article {927, title = {Generalized laws of thermodynamics in the presence of correlations}, journal = {Nature Communications}, volume = {8}, year = {2017}, month = {Jan-12-2017}, doi = {10.1038/s41467-017-02370-x}, url = {http://www.nature.com/articles/s41467-017-02370-xhttp://www.nature.com/articles/s41467-017-02370-x.pdfhttp://www.nature.com/articles/s41467-017-02370-x.pdfhttp://www.nature.com/articles/s41467-017-02370-x}, author = {Bera, Manabendra N. and Riera, Arnau and Lewenstein, Maciej and Winter, Andreas} } @article {clivaz_genuine-multipartite_2017, title = {Genuine-multipartite entanglement criteria based on positive maps}, journal = {JOURNAL OF MATHEMATICAL PHYSICS}, volume = {58}, number = {8}, year = {2017}, month = {aug}, abstract = {Positive maps applied to a subsystem of a bipartite quantum state constitute a central tool in characterising entanglement. In the multipartite case, however, the direct application of a positive but not completely positive map cannot distinguish if a state is genuinely multipartite entangled or just entangled across some bipartition. We thus generalise this bipartite concept to the multipartite setting by introducing non-positive maps that are positive on the subset of biseparable states but can map to a non-positive element if applied to a genuine multipartite entangled state. We explicitly construct examples of multipartite non-positive maps, obtained from positive maps via a lifting procedure, that in this fashion can reveal genuine multipartite entanglement in a robust way. Published by AIP Publishing.}, issn = {0022-2488}, doi = {10.1063/1.4998433}, author = {Clivaz, Fabien and Huber, Marcus and Lami, Ludovico and Murta, Glaucia} } @article {campbell_global_2017, title = {Global and local thermometry schemes in coupled quantum systems}, journal = {NEW JOURNAL OF PHYSICS}, volume = {19}, year = {2017}, month = {oct}, abstract = {We study the ultimate bounds on the estimation of temperature for an interacting quantum system. We consider two coupled bosonic modes that are assumed to be thermal and using quantum estimation theory establish the role the Hamiltonian parameters play in thermometry. We show that in the case of a conserved particle number the interaction between the modes leads to a decrease in the overall sensitivity to temperature, while interestingly, if particle exchange is allowed with the thermal bath the converse is true. We explain this dichotomy by examining the energy spectra. Finally, we devise experimentally implementable thermometry schemes that rely only on locally accessible information from the total system, showing that almost Heisenberg limited precision can still be achieved, and we address the (im)possibility for multiparameter estimation in the system.}, issn = {1367-2630}, doi = {10.1088/1367-2630/aa7fac}, author = {Campbell, Steve and Mehboudi, Mohammad and De Chiara, Gabriele and Paternostro, Mauro} } @article {munoz-tapia_heating_2017, title = {Heating without heat: Thermodynamics of passive energy filters between finite systems}, journal = {PHYSICAL REVIEW E}, volume = {96}, number = {3}, year = {2017}, abstract = {Passive filters allowing the exchange of particles in a narrow band of energy are currently used in microrefrigerators and energy transducers. In this Rapid Communication, we analyze their thermal properties using linear irreversible thermodynamics and kinetic theory, and discuss a striking phenomenon: the possibility of simultaneously increasing or decreasing the temperatures of two systems without any supply of energy. This occurs when the filter induces a flow of particles whose energy is between the average energies of the two systems. Here we show that this selective transfer of particles does not need the action of any sort of Maxwell demon and can be carried out by passive filters without compromising the second law of thermodynamics. This phenomenon allows us to design cycles between two reservoirs at temperatures T-1 {\textless} T-2 that are able to reach temperatures below T-1 or above T-2.

}, issn = {2470-0045}, doi = {10.1103/PhysRevE.96.030103}, author = {Mu{\~n}oz-Tapia, R. and Brito, R. and Parrondo, J. M. R.} } @article {sekatski_improved_2017, title = {Improved Sensing with a Single Qubit}, journal = {PHYSICAL REVIEW LETTERS}, volume = {118}, number = {17}, year = {2017}, abstract = {We consider quantum metrology with arbitrary prior knowledge of the parameter. We demonstrate that a single sensing two-level system can act as a virtual multilevel system that offers increased sensitivity in a Bayesian single-shot metrology scenario, and that allows one to estimate (arbitrary) large parameter values by avoiding phase wraps. This is achieved by making use of additional degrees of freedom or auxiliary systems not participating in the sensing process. The joint system is manipulated by intermediate control operations in such a way that an effective Hamiltonian, with an arbitrary spectrum, is generated that mimics the spectrum of a multisystem interacting with the field. We show how to use additional internal degrees of freedom of a single trapped ion to achieve a high-sensitivity magnetic field sensor for fields with arbitrary prior knowledge.

}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.118.170801}, author = {Sekatski, P. and Skotiniotis, M. and Duer, W.} } @conference {noetzel_information_2017, title = {Information Theoretic Principles of Universal Discrete Denoising}, booktitle = {2017 {INTERNATIONAL} {SYMPOSIUM} {ON} {WIRELESS} {COMMUNICATION} {SYSTEMS} ({ISWCS})}, series = {International {Symposium} on {Wireless} {Communication} {Systems}}, year = {2017}, pages = {205{\textendash}210}, abstract = {Social media platforms make tremendous amounts of data available. Often times, the same information is behind multiple different available data sets. This lends growing importance to latent variable models that try to learn the hidden information from the available imperfect versions. For example, social media platforms can contain an abundance of pictures of the same person, yet all of which are taken from different perspectives. In a simplified scenario, one may consider pictures taken from the same perspective, which are distorted by noise. This latter application allows for a rigorous mathematical treatment, which is the content of this contribution. We apply a recently developed method of dependent component analysis to image denoising when multiple distorted copies of one and the same image are available, each being corrupted by a different and unknown noise process. In a simplified scenario, one may assume such a distorted image to be corrupted by noise that acts independently on each pixel. We answer completely the question of how to perform optimal denoising, when at least three distorted copies are available: First we define optimality of an algorithm in the presented scenario, and then we describe an aymptotically optimal universal discrete denoising algorithm (UDDA).

}, isbn = {978-1-5386-2913-0}, author = {Noetzel, Janis and Winter, Andreas} } @article {biswas_interferometric_2017, title = {Interferometric visibility and coherence}, journal = {PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES}, volume = {473}, number = {2203}, year = {2017}, abstract = {Recently, the basic concept of quantum coherence (or superposition) has gained a lot of renewed attention, after Baumgratz et al. (Phys. Rev. Lett. 113, 140401. (doi: 10.1103/PhysRevLett.113.140401)), following Aberg (http://arxiv.org/abs/quant-ph/0612146), have proposed a resource theoretic approach to quantify it. This has resulted in a large number of papers and preprints exploring various coherence monotones, and debating possible forms for the resource theory. Here, we take the view that the operational foundation of coherence in a state, be it quantum or otherwise wave mechanical, lies in the observation of interference effects. Our approach here is to consider an idealized multi-path interferometer, with a suitable detector, in such a way that the visibility of the interference pattern provides a quantitative expression of the amount of coherence in a given probe state. We present a general framework of deriving coherence measures from visibility, and demonstrate it by analysing several concrete visibility parameters, recovering some known coherence measures and obtaining some new ones.}, issn = {1364-5021}, doi = {10.1098/rspa.2017.0170}, author = {Biswas, Tanmoy and Garcia Diaz, Maria and Winter, Andreas} } @article {rana_logarithmic_2017, title = {Logarithmic coherence: Operational interpretation of l(1)-norm coherence}, journal = {PHYSICAL REVIEW A}, volume = {96}, number = {5}, year = {2017}, abstract = {We show that the distillable coherence-which is equal to the relative entropy of coherence-is, up to a constant factor, always bounded by the l(1)-norm measure of coherence (defined as the sum of absolute values of off diagonals). Thus the latter plays a similar role as logarithmic negativity plays in entanglement theory and this is the best operational interpretation from a resource-theoretic viewpoint. Consequently the two measures are intimately connected to another operational measure, the robustness of coherence. We find also relationships between these measures, which are tight for general states, and the tightest possible for pure and qubit states. For a given robustness, we construct a state having minimum distillable coherence.

}, issn = {2469-9926}, doi = {10.1103/PhysRevA.96.052336}, author = {Rana, Swapan and Parashar, Preeti and Winter, Andreas and Lewenstein, Maciej} } @article {skotiniotis_macroscopic_2017, title = {Macroscopic superpositions require tremendous measurement devices}, journal = {Quantum}, volume = {1}, year = {2017}, month = {nov}, pages = {34}, abstract = {Michalis Skotiniotis, Wolfgang D{\"u}r, and Pavel Sekatski, Quantum 1, 34 (2017). https://doi.org/10.22331/q-2017-11-21-34 We consider fundamental limits on the detectable size of macroscopic quantum superpositions. We argue that a full quantum mechanical treatment of system plus measurement device is required,{\textellipsis}}, doi = {10.22331/q-2017-11-21-34}, url = {https://quantum-journal.org/papers/q-2017-11-21-34/}, author = {Skotiniotis, Michalis and D{\"u}r, Wolfgang and Sekatski, Pavel} } @article {mcalpine_magnetic_2017, title = {Magnetic phases of spin-1 lattice gases with random interactions}, journal = {PHYSICAL REVIEW B}, volume = {95}, number = {23}, year = {2017}, month = {jun}, abstract = {A spin-1 atomic gas in an optical lattice, in the unit-filling Mott insulator (MI) phase and in the presence of disordered spin-dependent interaction, is considered. In this regime, at zero temperature, the system is well described by a disordered rotationally invariant spin-1 bilinear-biquadratic model. We study, via the density matrix renormalization group algorithm, a bounded disorder model such that the spin interactions can be locally either ferromagnetic or antiferromagnetic. Random interactions induce the appearance of a disordered ferromagnetic phase characterized by a nonvanishing value of the spin glass order parameter across the boundary between a ferromagnetic phase and a dimer phase exhibiting random singlet order. We also study the distribution of the block entanglement entropy in the different regions.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.95.235128}, author = {McAlpine, Kenneth D. and Paganelli, Simone and Ciuchi, Sergio and Sanpera, Anna and De Chiara, Gabriele} } @article {perarnau-llobet_no-go_2017, title = {No-Go Theorem for the Characterization of Work Fluctuations in Coherent Quantum Systems}, journal = {PHYSICAL REVIEW LETTERS}, volume = {118}, number = {7}, year = {2017}, abstract = {An open question of fundamental importance in thermodynamics is howto describe the fluctuations of work for quantum coherent processes. In the standard approach, based on a projective energy measurement both at the beginning and at the end of the process, the first measurement destroys any initial coherence in the energy basis. Here we seek extensions of this approach which can possibly account for initially coherent states. We consider all measurement schemes to estimate work and require that (i) the difference of average energy corresponds to average work for closed quantum systems and that (ii) the work statistics agree with the standard two-measurement scheme for states with no coherence in the energy basis. We first show that such a scheme cannot exist. Next, we consider the possibility of performing collective measurements on several copies of the state and prove that it is still impossible to simultaneously satisfy requirements (i) and (ii). Nevertheless, improvements do appear, and in particular, we develop a measurement scheme that acts simultaneously on two copies of the state and allows us to describe a whole class of coherent transformations.

}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.118.070601}, author = {Perarnau-Llobet, Marti and Baumer, Elisa and Hovhannisyan, Karen V. and Huber, Marcus and Ac{\'\i}n, Antonio} } @article {sabapathy_non-gaussian_2017, title = {Non-{Gaussian} operations on bosonic modes of light: {Photon}-added {Gaussian} channels}, journal = {Physical Review A}, volume = {95}, number = {6}, year = {2017}, pages = {062309}, abstract = {We present a framework for studying bosonic non-Gaussian channels of continuous-variable systems. Our emphasis is on a class of channels that we call photon-added Gaussian channels, which are experimentally viable with current quantum-optical technologies. A strong motivation for considering these channels is the fact that it is compulsory to go beyond the Gaussian domain for numerous tasks in continuous-variable quantum information processing such as entanglement distillation from Gaussian states and universal quantum computation. The single-mode photon-added channels we consider are obtained by using two-mode beam splitters and squeezing operators with photon addition applied to the ancilla ports giving rise to families of non-Gaussian channels. For each such channel, we derive its operator-sum representation, indispensable in the present context. We observe that these channels are Fock preserving (coherence nongenerating). We then report two examples of activation using our scheme of photon addition, that of quantum-optical nonclassicality at outputs of channels that would otherwise output only classical states and of both the quantum and private communication capacities, hinting at far-reaching applications for quantum-optical communication. Further, we see that noisy Gaussian channels can be expressed as a convex mixture of these non-Gaussian channels. We also present other physical and information-theoretic properties of these channels.}, doi = {10.1103/PhysRevA.95.062309}, url = {https://link.aps.org/doi/10.1103/PhysRevA.95.062309}, author = {Sabapathy, Krishna Kumar and Winter, Andreas} } @article {erker_quantifying_2017, title = {Quantifying high dimensional entanglement with two mutually unbiased bases}, journal = {Quantum}, volume = {1}, year = {2017}, pages = {22}, abstract = {Paul Erker, Mario Krenn, and Marcus Huber, Quantum 1, 22 (2017). https://doi.org/10.22331/q-2017-07-28-22 We derive a framework for quantifying entanglement in multipartite and high dimensional systems using only correlations in two unbiased bases. We furthermore develop such bounds in cases whe{\textellipsis}}, doi = {10.22331/q-2017-07-28-22}, url = {https://quantum-journal.org/papers/q-2017-07-28-22/}, author = {Erker, Paul and Krenn, Mario and Huber, Marcus} } @article {sekatski_quantum_2017, title = {Quantum metrology with full and fast quantum control}, journal = {Quantum}, volume = {1}, year = {2017}, month = {sep}, pages = {27}, abstract = {Pavel Sekatski, Michalis Skotiniotis, Janek Ko{\l}ody{\'n}ski, and Wolfgang D{\"u}r, Quantum 1, 27 (2017). https://doi.org/10.22331/q-2017-09-06-27 We establish general limits on how precise a parameter, e.g. frequency or the strength of a magnetic field, can be estimated with the aid of full and fast quantum control. We consider uncorr{\textellipsis}}, doi = {10.22331/q-2017-09-06-27}, url = {https://quantum-journal.org/papers/q-2017-09-06-27/}, author = {Sekatski, Pavel and Skotiniotis, Michalis and Ko{\l}ody{\'n}ski, Janek and D{\"u}r, Wolfgang} } @article {805, title = {Quantum optics and frontiers of physics: the third quantum revolution}, journal = {Physica Scripta}, volume = {92}, year = {2017}, month = {Jan-01-2017}, pages = {013003}, issn = {0031-8949}, doi = {10.1088/1402-4896/92/1/013003}, url = {http://stacks.iop.org/1402-4896/92/i=1/a=013003?key=crossref.1d2d860672d166faed2db4e6d4b217abhttp://stacks.iop.org/1402-4896/92/i=1/a=013003/pdfhttp://stacks.iop.org/1402-4896/92/i=1/a=013003?key=crossref.1d2d860672d166faed2db4e6d4b217ab}, author = {Celi, Alessio and Sanpera, Anna and Ahufinger, Veronica and Lewenstein, Maciej} } @article {ben_dana_resource_2017, title = {Resource theory of coherence: Beyon} states}, journal = {PHYSICAL REVIEW A}, volume = {95}, number = {6}, year = {2017}, abstract = {We generalize the recently proposed resource theory of coherence (or superposition) [T. Baumgratz et al., Phys. Rev. Lett. 113, 140401 (2014); A. Winter and D. Yang, Phys. Rev. Lett. 116, 120404 ( 2016)] to the setting where not just the free ({\textquotedblright}incoherent{\textquotedblright}) resources, but also the manipulated objects, are quantum operations rather than states. In particular, we discuss an information theoretic notion of the coherence capacity of a quantum channel and prove a single-letter formula for it in the case of unitaries. Then we move to the coherence cost of simulating a channel and prove achievability results for unitaries and general channels acting on a d-dimensional system; we show that a maximally coherent state of rank d is always sufficient as a resource if incoherent operations are allowed, and one of rank d(2) for {\textquotedblleft}strictly incoherent{\textquotedblright} operations. We also show lower bounds on the simulation cost of channels that allow us to conclude that there exists bound coherence in operations, i.e., maps with nonzero cost of implementing them but zero coherence capacity; this is in contrast to states, which do not exhibit bound coherence.

}, issn = {2469-9926}, doi = {10.1103/PhysRevA.95.062327}, author = {Ben Dana, Khaled and Garcia Diaz, Maria and Mejatty, Mohamed and Winter, Andreas} } @article {ivan_scaling_2017, title = {Scaling maps of s-ordered quasiprobabilities are either nonpositive or completely positive}, journal = {PHYSICAL REVIEW A}, volume = {96}, number = {2}, year = {2017}, month = {aug}, abstract = {Continuous-variable systems in quantum theory can be fully described through any one of the s-ordered family of quasiprobabilities Lambda(s) (a), s is an element of [-1,1]. We ask forwhat values of (s,a) is the scalingmap Lambda(s) (alpha) -{\textgreater} a(-2) Lambda(s) (a(-1)alpha) a positive map? Our analysis based on a duality we establish settles this issue: (i) the scaling map generically fails to be positive, showing that there is no useful entanglement witness of the scaling type beyond the transpose map, and (ii) in the two particular cases (s = 1,{\textbar}a{\textbar} {\textless}= 1) and (s = -1,{\textbar}a{\textbar} {\textgreater}= 1), and only in these two nontrivial cases, the map is not only positive but also completely positive as seen through the noiseless attenuator and amplifier channels. We also present a {\textquotedblleft}phase diagram{\textquotedblright} for the behavior of the scaling maps in the s-a parameter space with regard to its positivity, obtained from the viewpoint of symmetric-ordered characteristic functions. This also sheds light on similar diagrams for the practically relevant attenuation and amplification maps with respect to the noise parameter, especially in the range below the complete-positivity (or quantum-limited) threshold.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.96.022114}, author = {Ivan, J. Solomon and Sabapathy, Krishna Kumar and Simon, R.} } @article {nakata_unitary_2017, title = {Unitary 2-designs from random X- and Z-diagonal unitaries}, journal = {JOURNAL OF MATHEMATICAL PHYSICS}, volume = {58}, number = {5}, year = {2017}, abstract = {Unitary 2-designs are random unitaries simulating up to the second order statistical moments of the uniformly distributed random unitaries, often referred to as Haar random unitaries. They are used in a wide variety of theoretical and practical quantum information protocols and also have been used to model the dynamics in complex quantum many-body systems. Here, we show that unitary 2-designs can be approximately implemented by alternately repeating random unitaries diagonal in the Pauli-Z basis and Pauli-X basis. We also provide a converse about the number of repetitions needed to achieve unitary 2-designs. These results imply that the process after l repetitions achieves a Theta(d(-l))-approximate unitary 2-design. Based on the construction, we further provide quantum circuits that efficiently implement approximate unitary 2-designs. Although a more efficient implementation of unitary 2-designs is known, our quantum circuit has its own merit that it is divided into a constant number of commuting parts, which enables us to apply all commuting gates simultaneously and leads to a possible reduction of an actual execution time. We finally interpret the result in terms of the dynamics generated by time-dependent Hamiltonians and provide for the first time a random disordered time-dependent Hamiltonian that generates a unitary 2-design after switching interactions only a few times. Published by AIP Publishing.

}, issn = {0022-2488}, doi = {10.1063/1.4983266}, author = {Nakata, Yoshifumi and Hirche, Christoph and Morgan, Ciara and Winter, Andreas} } @article {803, title = {Vortex stability in Bose-Einstein condensates in the presence of disorder}, journal = {Physical Review A}, volume = {95}, year = {2017}, month = {Jan-03-2017}, issn = {2469-9926}, doi = {10.1103/PhysRevA.95.033626}, url = {https://link.aps.org/doi/10.1103/PhysRevA.95.033626http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevA.95.033626/fulltexthttp://link.aps.org/article/10.1103/PhysRevA.95.033626}, author = {Pons, Marisa and Sanpera, Anna} } @article {780, title = {Achieving sub-shot-noise sensing at finite temperatures}, journal = {Physical Review A}, volume = {94}, year = {2016}, month = {10/2016}, issn = {2469-9934}, doi = {10.1103/PhysRevA.94.042121}, author = {Mehboudi, Mohammad and Correa, Luis A. and Sanpera, Anna} } @article {hofer_autonomous_2016, title = {Autonomous {Quantum} {Refrigerator} in a {Circuit}-{QED} {Architecture} {Based} on a {Josephson} {Junction}}, journal = {Physical Review B}, volume = {94}, number = {23}, year = {2016}, note = {arXiv: 1607.05218}, abstract = {An implementation of a small quantum absorption refrigerator in a circuit QED architecture is proposed. The setup consists of three harmonic oscillators coupled to a Josephson unction. The refrigerator is autonomous in the sense that it does not require any external control for cooling, but only thermal contact between the oscillators and heat baths at different temperatures. In addition, the setup features a built-in switch, which allows the cooling to be turned on and off. If timing control is available, this enables the possibility for coherence-enhanced cooling. Finally, we show that significant cooling can be achieved with experimentally realistic parameters and that our setup should be within reach of current technology.}, keywords = {Condensed Matter - Mesoscale and Nanoscale Physics, Quantum Physics}, issn = {2469-9950, 2469-9969}, doi = {10.1103/PhysRevB.94.235420}, url = {http://arxiv.org/abs/1607.05218}, author = {Hofer, Patrick P. and Perarnau-Llobet, Marti and Brask, Jonatan Bohr and Silva, Ralph and Huber, Marcus and Brunner, Nicolas} } @article {lami_bipartite_2016, title = {Bipartite depolarizing maps}, journal = {Journal of Mathematical Physics}, volume = {57}, number = {9}, year = {2016}, pages = {092201}, abstract = {We introduce a 3-parameter class of maps (1) acting on a bipartite system which are a natural generalisation of the depolarizing channel (and include it as a special case). Then, we find the exact regions of the parameter space that alternatively determine a positive, completely positive, entanglement-breaking, or entanglement-annihilating map. This model displays a much richer behaviour than the one shown by a simple depolarizing channel, yet it stays exactly solvable. As an example of this richness, positive partial transposition but not entanglement-breaking maps is found in Theorem 2. A simple example of a positive yet indecomposable map is provided (see the Remark at the end of Section IV). The study of the entanglement-annihilating property is fully addressed by Theorem 7. Finally, we apply our results to solve the problem of the entanglement annihilation caused in a bipartite system by a tensor product of local depolarizing channels. In this context, a conjecture posed in the work of Filippov [J. Russ. Laser Res. 35, 484 (2014)] is affirmatively answered, and the gaps that the imperfect bounds of Filippov and Ziman [Phys. Rev. A 88, 032316 (2013)] left open are closed. To arrive at this result, we furthermore show how the Hadamard product between quantum states can be implemented via local operations.}, issn = {0022-2488}, doi = {10.1063/1.4962339}, url = {http://aip.scitation.org/doi/10.1063/1.4962339}, author = {Lami, Ludovico and Huber, Marcus} } @article {karumanchi_classical_2016, title = {Classical capacities of quantum channels with environment assistance}, journal = {Problems of Information Transmission}, volume = {52}, number = {3}, year = {2016}, month = {jul}, pages = {214{\textendash}238}, abstract = {A quantum channel physically is a unitary interaction between an information carrying system and an environment, which is initialized in a pure state before the interaction. Conventionally, this state, as also the parameters of the interaction, is assumed to be fixed and known to the sender and receiver. Here, following the model introduced by us earlier [1], we consider a benevolent third party, i.e., a helper, controlling the environment state, and show how the helper{\textquoteright}s presence changes the communication game. In particular, we define and study the classical capacity of a unitary interaction with helper, in two variants: one where the helper can only prepare separable states across many channel uses, and one without this restriction. Furthermore, two even more powerful scenarios of pre-shared entanglement between helper and receiver, and of classical communication between sender and helper (making them conferencing encoders) are considered.}, issn = {0032-9460, 1608-3253}, doi = {10.1134/S0032946016030029}, url = {https://link.springer.com/article/10.1134/S0032946016030029}, author = {Karumanchi, S. and Mancini, S. and Winter, A. and Yang, D.} } @article {747, title = {Conditional and unconditional Gaussian quantum dynamics}, journal = {Contemporary Physics}, year = {2016}, month = {01/2016}, pages = {1 - 19}, issn = {1366-5812}, doi = {10.1080/00107514.2015.1125624}, author = {Genoni, Marco G. and Lami, Ludovico and Serafini, Alessio} } @article {800, title = {Entanglement and Coherence in Quantum State Merging}, journal = {Physical Review Letters}, volume = {116}, year = {2016}, month = {Jan-06-2016}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.116.240405}, url = {http://link.aps.org/doi/10.1103/PhysRevLett.116.240405http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevLett.116.240405/fulltexthttp://link.aps.org/accepted/10.1103/PhysRevLett.116.240405http://link.aps.org/article/10.1103/PhysRevLett.116.240405}, author = {Streltsov, A. and Chitambar, E. and Rana, S. and Bera, N. and Winter, A. and Lewenstein, M.} } @article {748, title = {Entanglement-saving channels}, journal = {Journal of Mathematical Physics}, volume = {57}, year = {2016}, month = {03/2016}, pages = {032201}, issn = {1089-7658}, doi = {10.1063/1.4942495}, author = {Lami, L. and Giovannetti, V.} } @article {677, title = {Estimating quantum chromatic numbers}, journal = {Journal of Functional Analysis}, volume = {270}, number = {6}, year = {2016}, month = {03/2016}, pages = {2188-2222}, issn = {00221236}, doi = {10.1016/j.jfa.2016.01.010}, author = {Paulsen, Vern I. and Severini, Simone and Stahlke, Daniel and Todorov, Ivan G. and Winter, Andreas} } @article {asadian_heisenberg-weyl_2016, title = {Heisenberg-{Weyl} {Observables}: {Bloch} vectors in phase space}, journal = {Physical Review A}, volume = {94}, number = {1}, year = {2016}, month = {jul}, pages = {010301}, abstract = {We introduce a Hermitian generalization of Pauli matrices to higher dimensions which is based on Heisenberg-Weyl operators. The complete set of Heisenberg-Weyl observables allows us to identify a real-valued Bloch vector for an arbitrary density operator in discrete phase space, with a smooth transition to infinite dimensions. Furthermore, we derive bounds on the sum of expectation values of any set of anticommuting observables. Such bounds can be used in entanglement detection and we show that Heisenberg-Weyl observables provide a first nontrivial example beyond the dichotomic case.}, doi = {10.1103/PhysRevA.94.010301}, url = {https://link.aps.org/doi/10.1103/PhysRevA.94.010301}, author = {Asadian, Ali and Erker, Paul and Huber, Marcus and Klockl, Claude} } @article {801, title = {Microcanonical and resource-theoretic derivations of the thermal state of a quantum system with noncommuting charges}, journal = {Nature Communications}, volume = {77}, year = {2016}, month = {Jul-07-2016}, pages = {12051}, doi = {10.1038/ncomms12051}, url = {http://www.nature.com/doifinder/10.1038/ncomms12051}, author = {Yunger Halpern, Nicole and Faist, Philippe and Oppenheim, Jonathan and Winter, Andreas} } @article {738, title = {Multi-photon entanglement in high dimensions}, journal = {Nature Photonics}, volume = {10}, year = {2016}, month = {04/2016}, pages = {248 - 252}, publisher = {Nature Publishing Group}, isbn = {1749-4885}, url = {http://dx.doi.org/10.1038/nphoton.2016.12}, author = {Malik, Mehul and Erhard, Manuel and Huber, Marcus and Krenn, Mario and Robert Fickler and Anton Zeilinger} } @article {695, title = {No-Signalling-Assisted Zero-Error Capacity of Quantum Channels and an Information Theoretic Interpretation of the Lov{\'a}sz Number}, journal = {IEEE Transactions on Information Theory}, volume = {62}, number = {2}, year = {2016}, month = {2/2016}, pages = {891-914}, issn = {1557-9654}, doi = {10.1109/TIT.2015.2507979}, author = {Duan, Runyao and Winter, Andreas} } @article {679, title = {Operational Resource Theory of Coherence}, journal = {Physical Review Letters}, volume = {116}, year = {2016}, month = {3/2016}, pages = {120404}, issn = {1079-7114}, doi = {10.1103/PhysRevLett.116.120404}, author = {Winter, Andreas and Dong Yang} } @article {710, title = {Polar Codes in Network Quantum Information Theory}, journal = {IEEE Transactions on Information Theory}, volume = {62}, year = {2016}, month = {02/2016}, pages = {915 - 924}, issn = {1557-9654}, doi = {10.1109/TIT.2016.2514319}, author = {Christoph Hirche and Ciara Morgan and Wilde, Mark M.} } @article {680, title = {Potential Capacities of Quantum Channels}, journal = {IEEE Transactions on Information Theory}, volume = {62}, number = {3}, year = {2016}, month = {3/2016}, pages = {1415-1424}, issn = {1557-9654}, doi = {10.1109/TIT.2016.2519920}, author = {Winter, Andreas and Dong Yang} } @article {698, title = {The Private and Public Correlation Cost of Three Random Variables With Collaboration}, journal = {IEEE Transactions on Information Theory}, volume = {62}, number = {4}, year = {2016}, month = {4/2016}, pages = {2034-2043}, issn = {1557-9654}, doi = {10.1109/TIT.2016.2530086}, author = {Eric Chitambar and Hsieh, Min-Hsiu and Winter, Andreas} } @article {787, title = {Probabilistic metrology or how some measurement outcomes render ultra-precise estimates}, journal = {New Journal of Physics}, volume = {18}, year = {2016}, month = {Jan-10-2016}, pages = {103049}, abstract = {We show on theoretical grounds that, even in the presence of noise, probabilistic measurement strategies (which have a certain probability of failure or abstention) can provide, upon a heralded successful outcome, estimates with a precision that exceeds the deterministic bounds for the average precision. This establishes a new ultimate bound on the phase estimation precision of particular measurement outcomes (or sequence of outcomes). For probe systems subject to local dephasing, we quantify such precision limit as a function of the probability of failure that can be tolerated. Our results show that the possibility of abstaining can set back the detrimental effects of noise.\

}, doi = {10.1088/1367-2630/18/10/103049}, url = {http://stacks.iop.org/1367-2630/18/i=10/a=103049?key=crossref.fb78efa5084e8d9fdb51f574cf3bfed3http://stacks.iop.org/1367-2630/18/i=10/a=103049/pdfhttp://stacks.iop.org/1367-2630/18/i=10/a=103049?key=crossref.fb78efa5084e8d9fdb51f574cf3bfed3}, author = {Calsamiglia, J and Gendra, B and Mu{\~n}oz-Tapia, R and Bagan, E} } @article {765, title = {Probabilistically Perfect Cloning of Two Pure States: Geometric Approach}, journal = {Physical Review Letters}, volume = {116}, year = {2016}, month = {5/2016}, issn = {1079-7114}, doi = {10.1103/PhysRevLett.116.200401}, author = {Yerokhin, V. and Shehu, A. and Feldman, E. and E. Bagan and Bergou, J. A.} } @article {701, title = {Process output nonclassicality and nonclassicality depth of quantum-optical channels}, journal = {Physical Review A}, volume = {93}, year = {2016}, month = {4/2016}, issn = {2469-9934}, doi = {10.1103/PhysRevA.93.042103}, author = {Sabapathy, Krishna Kumar} } @article {sentis_quantifying_2016, title = {Quantifying {Entanglement} of {Maximal} {Dimension} in {Bipartite} {Mixed} {States}}, journal = {Physical Review Letters}, volume = {117}, number = {19}, year = {2016}, pages = {190502}, abstract = {The Schmidt coefficients capture all entanglement properties of a pure bipartite state and therefore determine its usefulness for quantum information processing. While the quantification of the corresponding properties in mixed states is important both from a theoretical and a practical point of view, it is considerably more difficult, and methods beyond estimates for the concurrence are elusive. In particular this holds for a quantitative assessment of the most valuable resource, the forms of entanglement that can only exist in high-dimensional systems. We derive a framework for lower bounding the appropriate measure of entanglement, the so-called G-concurrence, through few local measurements. Moreover, we show that these bounds have relevant applications also for multipartite states.}, doi = {10.1103/PhysRevLett.117.190502}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.117.190502}, author = {Sent{\'\i}s, Gael and Eltschka, Christopher and G{\"u}hne, Otfried and Huber, Marcus and Siewert, Jens} } @article {784, title = {Quantum Change Point}, journal = {Physical Review Letters}, volume = {117}, year = {2016}, month = {Jan-10-2016}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.117.150502}, url = {http://link.aps.org/doi/10.1103/PhysRevLett.117.150502http://link.aps.org/article/10.1103/PhysRevLett.117.150502}, author = {Sent{\'\i}s, Gael and Bagan, Emilio and Calsamiglia, John and Chiribella, Giulio and Mu{\~n}oz-Tapia, Ramon} } @article {685, title = {Quantum Channel Capacities With Passive Environment Assistance}, journal = {IEEE Transactions on Information Theory}, volume = {62}, number = {4}, year = {2016}, month = {4/2016}, pages = {1733-1747}, issn = {1557-9654}, doi = {10.1109/TIT.2016.2522192}, author = {Karumanchi, Siddharth and Mancini, Stefano and Winter, Andreas and Dong Yang} } @article {696, title = {Quantum learning of classical stochastic processes: The completely positive realization problem}, journal = {Journal of Mathematical Physics}, volume = {57}, number = {1}, year = {2016}, month = {01/2016}, pages = {015219}, issn = {1089-7658}, doi = {10.1063/1.4936935}, author = {Monr{\`a}s, Alex and Winter, Andreas} } @article {mitchison_realising_2016, title = {Realising a quantum absorption refrigerator with an atom-cavity system}, journal = {Quantum Science and Technology}, volume = {1}, number = {1}, year = {2016}, pages = {015001}, abstract = {An autonomous quantum thermal machine comprising a trapped atom or ion placed inside an optical cavity is proposed and analysed. Such a machine can operate as a heat engine whose working medium is the quantised atomic motion or as an absorption refrigerator that cools without any work input. Focusing on the refrigerator mode, we predict that it is possible with state-of-the-art technology to cool a trapped ion almost to its motional ground state using a thermal light source such as sunlight. We nonetheless find that a laser or a similar reference system is necessary to stabilise the cavity frequencies. Furthermore, we establish a direct and heretofore unacknowledged connection between the abstract theory of quantum absorption refrigerators and practical sideband cooling techniques. We also highlight and clarify some assumptions underlying several recent theoretical studies on self-contained quantum engines and refrigerators. Our work indicates that cavity quantum electrodynamics is a promising and versatile experimental platform for the study of autonomous thermal machines in the quantum domain.}, issn = {2058-9565}, doi = {10.1088/2058-9565/1/1/015001}, url = {http://stacks.iop.org/2058-9565/1/i=1/a=015001}, author = {Mitchison, Mark T. and Huber, Marcus and Prior, Javier and Woods, Mischa P. and Plenio, Martin B.} } @article {PhysRevLett.116.160406, title = {Relations between Coherence and Path Information}, journal = {Phys. Rev. Lett.}, volume = {116}, year = {2016}, month = {Apr}, pages = {160406}, publisher = {American Physical Society}, doi = {10.1103/PhysRevLett.116.160406}, url = {http://link.aps.org/doi/10.1103/PhysRevLett.116.160406}, author = {E. Bagan and Bergou, J{\'a}nos A. and Cottrell, Seth S. and Hillery, Mark} } @article {goold_role_2016, title = {The role of quantum information in thermodynamics{\textemdash}a topical review}, journal = {Journal of Physics A: Mathematical and Theoretical}, volume = {49}, number = {14}, year = {2016}, pages = {143001}, issn = {1751-8113, 1751-8121}, doi = {10.1088/1751-8113/49/14/143001}, url = {http://stacks.iop.org/1751-8121/49/i=14/a=143001?key=crossref.ce80cac2171964cc6d6c51ed12d1e014}, author = {Goold, John and Huber, Marcus and Riera, Arnau and Rio, L{\'\i}dia del and Paul Skrzypczyk} } @article {799, title = {Schur Complement Inequalities for Covariance Matrices and Monogamy of Quantum Correlations}, journal = {Physical Review Letters}, volume = {117}, year = {2016}, month = {Jan-11-2016}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.117.220502}, url = {http://link.aps.org/doi/10.1103/PhysRevLett.117.220502http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevLett.117.220502/fulltexthttp://link.aps.org/article/10.1103/PhysRevLett.117.220502}, author = {Lami, Ludovico and Hirche, Christoph and Adesso, Gerardo and Winter, Andreas} } @article {777, title = {Should Entanglement Measures be Monogamous or Faithful?}, journal = {Physical Review Letters}, volume = {117}, year = {2016}, month = {8/2016}, issn = {1079-7114}, doi = {10.1103/PhysRevLett.117.060501}, author = {Lancien, C{\'e}cilia and Di Martino, Sara and Huber, Marcus and Piani, Marco and Adesso, Gerardo and Winter, Andreas} } @article {moroder_steering_2016, title = {Steering Maps and Their Application to Dimension-Bounded Steering}, journal = {Physical Review Letters}, volume = {116}, number = {9}, year = {2016}, issn = {0031-9007, 1079-7114}, doi = {10.1103/PhysRevLett.116.090403}, url = {http://link.aps.org/doi/10.1103/PhysRevLett.116.090403}, author = {Moroder, Tobias and Gittsovich, Oleg and Huber, Marcus and Uola, Roope and G{\"u}hne, Otfried} } @article {707, title = {Testing a Quantum Heat Pump with a Two-Level Spin}, journal = {Entropy}, volume = {18}, year = {2016}, month = {4/2016}, pages = {141}, doi = {10.3390/e18040141}, url = {http://www.mdpi.com/1099-4300/18/4/141/htm}, author = {Correa, Luis and Mehboudi, Mohammad} } @article {682, title = {Tight Uniform Continuity Bounds for Quantum Entropies: Conditional Entropy, Relative Entropy Distance and Energy Constraints}, journal = {Communications in Mathematical Physics}, volume = {347}, number = {1}, year = {2016}, month = {08/2016}, pages = {291-313}, issn = {1432-0916}, doi = {10.1007/s00220-016-2609-8}, url = {http://arxiv.org/abs/1507.07775}, author = {Winter, Andreas} } @article {681, title = {Weak Locking Capacity of Quantum Channels Can be Much Larger Than Private Capacity}, journal = {Journal of Cryptology}, year = {2016}, issn = {1432-1378}, doi = {10.1007/s00145-015-9215-3}, url = {http://arxiv.org/abs/1403.6361}, author = {Winter, Andreas} } @article {699, title = {Witnessing entanglement by proxy}, journal = {New Journal of Physics}, volume = {18}, number = {1}, year = {2016}, month = {01/2016}, pages = {015002}, doi = {10.1088/1367-2630/18/1/015002}, author = {B{\"a}uml, Stefan and Bru{\ss}, Dagmar and Huber, Marcus and Kampermann, Hermann and Winter, Andreas} } @article {duan_zero-error_2016, title = {On {Zero}-{Error} {Communication} via {Quantum} {Channels} in the {Presence} of {Noiseless} {Feedback}}, journal = {IEEE Transactions on Information Theory}, volume = {62}, number = {9}, year = {2016}, month = {sep}, pages = {5260{\textendash}5277}, abstract = {We initiate the study of zero-error communication via quantum channels when the receiver and the sender have at their disposal a noiseless feedback channel of unlimited quantum capacity, generalizing Shannon{\textquoteright}s zero-error communication theory with instantaneous feedback. We first show that this capacity is only a function of the linear span of Choi-Kraus operators of the channel, which generalizes the bipartite equivocation graph of a classical channel, and which we dub non-commutative bipartite graph. Then, we go on to show that the feedback-assisted capacity is non-zero (allowing for a constant amount of activating noiseless communication) if and only if the non-commutative bipartite graph is non-trivial, and give a number of equivalent characterizations. This result involves a far-reaching extension of the conclusive exclusion of quantum states. We then present an upper bound on the feedback-assisted zero-error capacity, motivated by a conjecture originally made by Shannon and proved later by Ahlswede. We demonstrate that this bound to have many good properties, including being additive and given by a minimax formula. We also prove a coding theorem showing that this quantity is the entanglement-assisted capacity against an adversarially chosen channel from the set of all channels with the same Choi-Kraus span, which can also be interpreted as the feedback-assisted unambiguous capacity. The proof relies on a generalization of the Postselection Lemma (de Finetti reduction) that allows to reflect additional constraints, and which we believe to be of independent interest. This capacity is a relaxation of the feedback-assisted zero-error capacity; however, we have to leave open the question of whether they coincide in general. We illustrate our ideas with a number of examples, including classical-quantum channels and Weyl diagonal channels, and close with an extensive discussion of open questions.}, keywords = {bipartite equivocation graph, Bipartite graph, Capacity planning, Choi-Kraus operators, coding theorem, commutative bipartite graph, Electronic mail, encoding, entanglement-assisted capacity, feedback, feedback-assisted capacity, feedback-assisted zero-error capacity, information theory, noiseless feedback channel, quantum channels, quantum communication, quantum entanglement, Quantum information, Receivers, Shannon{\textquoteright}s zero-error communication, telecommunication channels, unlimited quantum capacity, zero-error capacity}, issn = {0018-9448}, doi = {10.1109/TIT.2016.2562580}, author = {Duan, R. and Severini, S. and Winter, A.} } @article {bohr_brask_autonomous_2015, title = {Autonomous quantum thermal machine for generating steady-state entanglement}, journal = {New Journal of Physics}, volume = {17}, number = {11}, year = {2015}, month = {nov}, pages = {113029}, issn = {1367-2630}, doi = {10.1088/1367-2630/17/11/113029}, url = {http://stacks.iop.org/1367-2630/17/i=11/a=113029?key=crossref.0c6a75cb628f113c6cbd2a7b0d092f0d}, author = {Bohr Brask, Jonatan and Haack, G{\'e}raldine and Nicolas Brunner and Huber, Marcus} } @article {klockl_characterizing_2015, title = {Characterizing multipartite entanglement without shared reference frames}, journal = {Physical Review A}, volume = {91}, number = {4}, year = {2015}, month = {apr}, issn = {1050-2947, 1094-1622}, doi = {10.1103/PhysRevA.91.042339}, url = {http://link.aps.org/doi/10.1103/PhysRevA.91.042339}, author = {Kl{\"o}ckl, C. and Huber, M} } @article {mitchison_coherence-assisted_2015, title = {Coherence-assisted single-shot cooling by quantum absorption refrigerators}, journal = {New Journal of Physics}, volume = {17}, number = {11}, year = {2015}, pages = {115013}, issn = {1367-2630}, doi = {10.1088/1367-2630/17/11/115013}, url = {http://stacks.iop.org/1367-2630/17/i=11/a=115013?key=crossref.3c2d7f1bc5de4bbea1cba38fd2236293}, author = {Mitchison, Mark T and Woods, Mischa P and Prior, Javier and Huber, Marcus} } @article {700, title = {Decoupling with random diagonal-unitary matrices}, year = {2015}, url = {http://arxiv.org/abs/1509.05155}, author = {Yoshifumi Nakata and Christoph Hirche and Ciara Morgan and Winter, Andreas} } @article {746, title = {Entanglement{\textendash}breaking indices}, journal = {Journal of Mathematical Physics}, volume = {56}, year = {2015}, month = {09/2015}, pages = {092201}, issn = {1089-7658}, doi = {10.1063/1.4931482}, author = {Lami, L. and Giovannetti, V.} } @article {Schaeff:15, title = {Experimental access to higher-dimensional entangled quantum systems using integrated optics}, journal = {Optica}, volume = {2}, number = {6}, year = {2015}, month = {Jun}, pages = {523{\textendash}529}, publisher = {OSA}, abstract = {Integrated optics allows for the generation and control of increasingly complex photonic states on chip-based architectures. Here, we implement two entangled qutrits\&\#x2014;a nine-dimensional quantum system\&\#x2014;and demonstrate an exceptionally high degree of experimental control. The approach, which is conceptually different to common bulk optical implementations, is heavily based on methods of integrated in-fiber and on-chip technologies and further motivated by methods commonly used in today\&\#x2019;s telecommunications industry. The system is composed of an in-fiber source creating entangled qutrit states of any amplitude and phase, and an on-chip integrated general Multiport enabling the realization of any desired local unitary transformation within the two qutrit nine-dimensional Hilbert space. The complete design is readily extendible toward higher dimensions with moderate increase in complexity. Ultimately, our scheme allows for complete on-chip integration. We demonstrate the flexibility and generality of our system by realizing a complete characterization of the two-qutrit space of higher-order Einstein\&\#x2013;Podolsky\&\#x2013;Rosen correlations.}, keywords = {Integrated optics, quantum optics}, doi = {10.1364/OPTICA.2.000523}, url = {http://www.osapublishing.org/optica/abstract.cfm?URI=optica-2-6-523}, author = {Christoph Schaeff and Robert Polster and Huber, Marcus and Ramelow, Sven and Anton Zeilinger} } @article {perarnau-llobet_extractable_2015, title = {Extractable Work from Correlations}, journal = {Physical Review X}, volume = {5}, number = {4}, year = {2015}, month = {oct}, issn = {2160-3308}, doi = {10.1103/PhysRevX.5.041011}, url = {http://link.aps.org/doi/10.1103/PhysRevX.5.041011}, author = {Mart{\'\i} Perarnau-Llobet and Karen V. Hovhannisyan and Huber, Marcus and Paul Skrzypczyk and Nicolas Brunner and Ac{\'\i}n, Antonio} } @article {1367-2630-17-12-123015, title = {A geometric approach to quantum state separation}, journal = {New Journal of Physics}, volume = {17}, number = {12}, year = {2015}, pages = {123015}, abstract = {Probabilistic quantum state transformations can be characterized by the degree of state separation they provide. This, in turn, sets limits on the success rate of these transformations. We consider optimum state separation of two known pure states in the general case where the known states have arbitrary a priori probabilities. The problem is formulated from a geometric perspective and shown to be equivalent to the problem of finding tangent curves within two families of conics that represent the unitarity constraints and the objective functions to be optimized, respectively. We present the corresponding analytical solutions in various forms. In the limit of perfect state separation, which is equivalent to unambiguous state discrimination, the solution exhibits a phenomenon analogous to a second order symmetry breaking phase transition. We also propose a linear optics implementation of separation which is based on the dual rail representation of qubits and single-photon multiport interferometry.}, url = {http://stacks.iop.org/1367-2630/17/i=12/a=123015}, author = {E. Bagan and Yerokhin, V. and Shehu, A. and Feldman, E. and Bergou, J. A.} } @article {702, title = {Implementing unitary 2-designs using random diagonal-unitary matrices}, year = {2015}, url = {http://arxiv.org/abs/1502.07514}, author = {Yoshifumi Nakata and Christoph Hirche and Ciara Morgan and Winter, Andreas} } @article {708, title = {Individual Quantum Probes for Optimal Thermometry}, journal = {Physical Review Letters}, volume = {114}, year = {2015}, month = {6/2015}, issn = {1079-7114}, doi = {10.1103/PhysRevLett.114.220405}, author = {Correa, Luis A. and Mehboudi, Mohammad and Adesso, Gerardo and Sanpera, Anna} } @article {690, title = {Limitations on quantum key repeaters}, journal = {Nature Communications}, volume = {6}, year = {2015}, month = {4/2015}, pages = {6908}, doi = {10.1038/ncomms7908}, author = {B{\"a}uml, Stefan and Christandl, Matthias and Horodecki, Karol and Winter, Andreas} } @article {638, title = {Mesoscopic superpositions of Tonks-Girardeau states and the Bose-Fermi mapping}, journal = {Physical Review A}, year = {2015}, abstract = {We study a one-dimensional gas of repulsively interacting ultracold bosons trapped in a double-well potential as the atom-atom interactions are tuned from zero to infinity. We concentrate on the properties of the excited states which evolve from the so-called NOON states to the NOON Tonks-Girardeau states. The relation between the latter and the Bose-Fermi mapping limit is explored. We state under which conditions NOON Tonks-Girardeau states, which are not predicted by the Bose-Fermi mapping, will appear in the spectrum.}, doi = {http://dx.doi.org/10.1103/PhysRevA.92.033621}, author = {M.A. Garc{\'\i}a-March and A.Yuste and B.Juli{\'a}-D{\'\i}az and A.Polls} } @article {perarnau-llobet_most_2015, title = {Most energetic passive states}, journal = {Physical Review E}, volume = {92}, number = {4}, year = {2015}, issn = {1539-3755, 1550-2376}, doi = {10.1103/PhysRevE.92.042147}, url = {http://link.aps.org/doi/10.1103/PhysRevE.92.042147}, author = {Mart{\'\i} Perarnau-Llobet and Karen V. Hovhannisyan and Huber, Marcus and Paul Skrzypczyk and Tura, Jordi and Ac{\'\i}n, Antonio} } @article {703, title = {Quantum-optical channels that output only classical states}, journal = {Physical Review A}, volume = {92}, year = {2015}, month = {11/2015}, issn = {1094-1622}, doi = {10.1103/PhysRevA.92.052301}, author = {Sabapathy, Krishna Kumar} } @article {lancien_relaxations_2015, title = {Relaxations of separability in multipartite systems: Semidefinite programs, witnesses and volumes}, journal = {Journal of Physics A: Mathematical and Theoretical}, volume = {48}, number = {50}, year = {2015}, pages = {505302}, issn = {1751-8113, 1751-8121}, doi = {10.1088/1751-8113/48/50/505302}, url = {http://stacks.iop.org/1751-8121/48/i=50/a=505302?key=crossref.2e93a28de5494676a0b866fa95ccebfd}, author = {Lancien, C{\'e}cilia and G{\"u}hne, Otfried and Sengupta, Ritabrata and Huber, Marcus} } @article {691, title = {Strong Converse for the Classical Capacity of Optical Quantum Communication Channels}, journal = {IEEE Transactions on Information Theory}, volume = {61}, number = {4}, year = {2015}, month = {4/2015}, pages = {1842-1850}, issn = {1557-9654}, doi = {10.1109/TIT.2015.2403840}, author = {Bardhan, Bhaskar Roy and Garcia-Patron, Raul and Wilde, Mark M. and Winter, Andreas} } @article {huber_thermodynamic_2015, title = {Thermodynamic cost of creating correlations}, journal = {New Journal of Physics}, volume = {17}, number = {6}, year = {2015}, pages = {065008}, issn = {1367-2630}, doi = {10.1088/1367-2630/17/6/065008}, url = {http://stacks.iop.org/1367-2630/17/i=6/a=065008?key=crossref.b9c20f4bb628b09efcb912347c01851e}, author = {Huber, Marcus and Mart{\'\i} Perarnau-Llobet and Karen V. Hovhannisyan and Paul Skrzypczyk and Kl{\"o}ckl, Claude and Nicolas Brunner and Ac{\'\i}n, Antonio} } @article {bruschi_thermodynamics_2015, title = {Thermodynamics of creating correlations: {Limitations} and optimal protocols}, journal = {Physical Review E}, volume = {91}, number = {3}, year = {2015}, month = {mar}, issn = {1539-3755, 1550-2376}, doi = {10.1103/PhysRevE.91.032118}, url = {http://link.aps.org/doi/10.1103/PhysRevE.91.032118}, author = {Bruschi, David Edward and Mart{\'\i} Perarnau-Llobet and Friis, Nicolai and Karen V. Hovhannisyan and Huber, Marcus} } @article {709, title = {Thermometry precision in strongly correlated ultracold lattice gases}, journal = {New Journal of Physics}, volume = {17}, year = {2015}, month = {05/2015}, pages = {055020}, doi = {10.1088/1367-2630/17/5/055020}, author = {Mehboudi, M and Moreno-Cardoner, M. and Chiara, G De and Sanpera, A.} } @article {578, title = {Best separable approximation of multipartite diagonal symmetric states}, journal = {Physical Review A}, volume = {89}, year = {2014}, month = {5/2014}, abstract = {The structural study of entanglement in multipartite systems is hindered by the lack of necessary and sufficient operational criteria able to discriminate among the various entanglement properties of a given mixed state. Here, we pursue a different route to the study of multipartite entanglement based on the closeness of a multipartite state to the set of separable ones. In particular, we analyze multipartite diagonal symmetric N-qubit states and provide the analytical expression for their best separable approximation (BSA, [Phys. Rev. Lett. 80, 2261 (1998)]), that is, their unique convex decomposition into a separable part and an entangled part, with maximal weight of the separable part.}, issn = {1094-1622}, doi = {10.1103/PhysRevA.89.052319}, author = {Quesada, Ruben and Sanpera, Anna} } @article {510, title = {Bounds on entanglement assisted source-channel coding via the Lovasz theta number and its variants}, journal = {IEEE Transactions on Information Theory}, volume = {60}, number = {11}, year = {2014}, month = {11/2014}, pages = {7330-7344}, doi = {10.1109/TIT.2014.2349502}, author = {Toby S. Cubitt and Laura Mancinska and David Roberson and Stahlke, Daniel and Winter, Andreas} } @article {577, title = {Case study of the uniaxial anisotropic spin-1 bilinear-biquadratic Heisenberg model on a triangular lattice}, journal = {Physical Review B}, volume = {90}, year = {2014}, month = {10/2014}, abstract = {We study the spin-1 model on a triangular lattice in the presence of a uniaxial anisotropy field using a cluster mean-field (CMF) approach. The interplay among antiferromagnetic exchange, lattice geometry, and anisotropy forces Gutzwiller mean-field approaches to fail in a certain region of the phase diagram. There, the CMF method yields two supersolid phases compatible with those present in the spin-1/2 XXZ model onto which the spin-1 system maps. Between these two supersolid phases, the three-sublattice order is broken and the results of the CMF approach depend heavily on the geometry and size of the cluster. We discuss the possible presence of a spin liquid in this region.}, issn = {1550-235X}, doi = {10.1103/PhysRevB.90.144409}, author = {Moreno-Cardoner, M. and Perrin, H. and Paganelli, S. and De Chiara, G. and Sanpera, A.} } @proceedings {692, title = {Constant compositions in the sphere packing bound for classical-quantum channels}, year = {2014}, month = {07/2014}, pages = {151-155}, publisher = {IEEE}, address = {Honolulu, HI, USA}, doi = {10.1109/ISIT.2014.6874813}, author = {Dalai, Marco and Winter, Andreas} } @mastersthesis {571, title = {Dealing with ignorance: universal discrimination, learning and quantum correlations}, year = {2014}, month = {06/2014}, school = {Universitat Aut{\`o}noma de Barcelona}, abstract = {The problem of discriminating the state of a quantum system among a number of hypothetical states is usually addressed under the assumption that one has perfect knowledge of the possible states of the system. In this thesis, I analyze the role of the prior information available in facing such problems, and consider scenarios where the information regarding the possible states is incomplete. In front of a complete ignorance of the possible states{\textquoteright} identity, I discuss a quantum "programmable" discrimination machine for qubit states that accepts this information as input programs using a quantum encoding, rather than as a classical description. The optimal performance of these machines is studied for general qubit states when several copies are provided, in the schemes of unambiguous, minimum-error, and error-margin discrimination. Then, this type of automation in discrimination tasks is taken further. By realizing a programmable machine as a device that is trained through quantum information to perform a specific task, I propose a quantum "learning" machine for classifying qubit states that does not require a quantum memory to store the qubit programs and, nevertheless, performs as good as quantum mechanics permits. Such learning machine thus allows for several optimal uses with no need for retraining. A similar learning scheme is also discussed for coherent states of light. I present it in the context of the readout of a classical memory by means of classically correlated coherent signals, when these are produced by an imperfect source. I show that, in this case, the retrieval of information stored in the memory can be carried out more accurately when fully general quantum measurements are used. Finally, as a transversal topic, I propose an efficient algorithmic way of decomposing any quantum measurement into convex combinations of simpler (extremal) measurements.}, url = {http://arxiv.org/abs/1407.4690}, author = {Sent{\'\i}s, Gael} } @article {568, title = {Entanglement enhances cooling in microscopic quantum refrigerators}, journal = {Physical Review E}, volume = {89}, year = {2014}, month = {3/2014}, abstract = {Small self-contained quantum thermal machines function without external source of work or control, but using only incoherent interactions with thermal baths. Here we investigate the role of entanglement in a small self-contained quantum refrigerator. We first show that entanglement is detrimental as far as efficiency is concerned---fridges operating at efficiencies close to the Carnot limit do not feature any entanglement. Moving away from the Carnot regime, we show that entanglement can enhance cooling and energy transport. Hence a truly quantum refrigerator can outperform a classical one. Furthermore, the amount of entanglement alone quantifies the enhancement in cooling.}, issn = {1550-2376}, doi = {10.1103/PhysRevE.89.032115}, author = {Nicolas Brunner and Huber, Marcus and Noah Linden and Sandu Popescu and Ralph Silva and Paul Skrzypczyk} } @article {580, title = {Entanglement properties of spin models in triangular lattices}, journal = {Journal of Statistical Mechanics: Theory and Experiment}, volume = {2014}, year = {2014}, month = {10/2014}, pages = {P10008}, abstract = {The different quantum phases appearing in strongly correlated systems as well as their transitions are closely related to the entanglement shared between their constituents. In 1D systems, it is well established that the entanglement spectrum is linked to the symmetries that protect the different quantum phases. This relation extends even further at the phase transitions where a direct link associates the entanglement spectrum to the conformal field theory describing the former. For 2D systems much less is known. The lattice geometry becomes a crucial aspect to consider when studying entanglement and phase transitions. Here, we analyze the entanglement properties of triangular spin lattice models by also considering concepts borrowed from quantum information theory such as geometric entanglement.}, doi = {10.1088/1742-5468/2014/10/P10008}, author = {Moreno-Cardoner, M. and Paganelli, S. and De Chiara, G. and Sanpera, A.} } @article {687, title = {Everything You Always Wanted to Know About LOCC (But Were Afraid to Ask)}, journal = {Communications in Mathematical Physics}, volume = {328}, number = {1}, year = {2014}, month = {5/2014}, pages = {303-326}, issn = {1432-0916}, doi = {10.1007/s00220-014-1953-9}, author = {Eric Chitambar and Debbie Leung and Man{\v c}inska, Laura and Maris Ozols and Winter, Andreas} } @article {brunner_fifty_2014, title = {Fifty years of Bell{\textquoteright}s theorem}, journal = {Journal of Physics A: Mathematical and Theoretical}, volume = {47}, number = {42}, year = {2014}, month = {oct}, pages = {420301}, issn = {1751-8113, 1751-8121}, doi = {10.1088/1751-8113/47/42/420301}, url = {http://stacks.iop.org/1751-8121/47/i=42/a=420301?key=crossref.9d548f14fc7338685392dcd6228de98d}, author = {Nicolas Brunner and G{\"u}hne, Otfried and Huber, Marcus} } @article {684, title = {Full Security of Quantum Key Distribution From No-Signaling Constraints}, journal = {IEEE Transactions on Information Theory}, volume = {60}, number = {8}, year = {2014}, month = {8/2014}, pages = {4973-4986}, issn = {1557-9654}, doi = {10.1109/TIT.2014.2329417}, author = {Masanes, Lluis and Renner, Renato and Christandl, Matthias and Winter, Andreas and Barrett, Jonathan} } @article {569, title = {Generation and confirmation of a (100 x 100)-dimensional entangled quantum system}, journal = {Proceedings of the National Academy of Sciences}, volume = {111}, year = {2014}, month = {04/2014}, pages = {6243 - 6247}, abstract = {Entangled quantum systems have properties that have fundamentally overthrown the classical worldview. Increasing the complexity of entangled states by expanding their dimensionality allows the implementation of novel fundamental tests of nature, and moreover also enables genuinely new protocols for quantum information processing. Here we present the creation of a (100x100)-dimensional entangled quantum system, using spatial modes of photons. For its verification we develop a novel nonlinear criterion which infers entanglement dimensionality of a global state by using only information about its subspace correlations. This allows very practical experimental implementation as well as highly efficient extraction of entanglement dimensionality information. Applications in quantum cryptography and other protocols are very promising.}, issn = {1091-6490}, doi = {10.1073/pnas.1402365111}, author = {Krenn, M. and Huber, M and Fickler, R. and Lapkiewicz, R. and Ramelow, S. and Zeilinger, A.} } @article {689, title = {Graph-Theoretic Approach to Quantum Correlations}, journal = {Physical Review Letters}, volume = {112}, number = {4}, year = {2014}, month = {1/2014}, pages = {040401}, issn = {1079-7114}, doi = {10.1103/PhysRevLett.112.040401}, author = {Cabello, Ad{\'a}n and Severini, Simone and Winter, Andreas} } @article {567, title = {Inequalities for the ranks of multipartite quantum states}, journal = {Linear Algebra and its Applications}, volume = {452}, year = {2014}, month = {07/2014}, pages = {153 - 171}, abstract = {We investigate relations between the ranks of marginals of multipartite quantum states. These are the Schmidt ranks across all possible bipartitions and constitute a natural quantification of multipartite entanglement dimensionality. We show that there exist inequalities constraining the possible distribution of ranks. This is analogous to the case of von Neumann entropy (\alpha-R\'enyi entropy for \alpha=1), where nontrivial inequalities constraining the distribution of entropies (such as e.g. strong subadditivity) are known. It was also recently discovered that all other \alpha-R\'enyi entropies for α∈(0,1)∪(1,$\infty$) satisfy only one trivial linear inequality (non-negativity) and the distribution of entropies for α∈(0,1) is completely unconstrained beyond non-negativity. Our result resolves an important open question by showing that also the case of \alpha=0 (logarithm of the rank) is restricted by nontrivial linear relations and thus the cases of von Neumann entropy (i.e., \alpha=1) and 0-R\'enyi entropy are exceptionally interesting measures of entanglement in the multipartite setting.}, issn = {00243795}, doi = {10.1016/j.laa.2014.03.035}, author = {Josh Cadney and Huber, Marcus and Noah Linden and Winter, Andreas} } @article {560, title = {Interface between path and orbital angular momentum entanglement for high-dimensional photonic quantum information}, journal = {Nature Communications}, volume = {5}, year = {2014}, month = {7/2014}, abstract = {Photonics has become a mature field of quantum information science, where integrated optical circuits offer a way to scale the complexity of the setup as well as the dimensionality of the quantum state. On photonic chips, paths are the natural way to encode information. To distribute those high-dimensional quantum states over large distances, transverse spatial modes, like orbital angular momentum (OAM) possessing Laguerre Gauss modes, are favourable as flying information carriers. Here we demonstrate a quantum interface between these two vibrant photonic fields. We create three-dimensional path entanglement between two photons in a non-linear crystal and use a mode sorter as the quantum interface to transfer the entanglement to the OAM degree of freedom. Thus our results show a novel, flexible way to create high-dimensional spatial mode entanglement. Moreover, they pave the way to implement broad complex quantum networks where high-dimensionally entangled states could be distributed over distant photonic chips.}, doi = {10.1038/ncomms5502}, author = {Robert Fickler and Radek Lapkiewicz and Huber, Marcus and Lavery, Martin P.J. and Padgett, Miles J. and Anton Zeilinger} } @article {579, title = {Long-range multipartite entanglement close to a first-order quantum phase transition}, journal = {Physical Review A}, volume = {89}, year = {2014}, month = {3/2014}, abstract = {We provide insight into the quantum correlations structure present in strongly correlated systems beyond the standard framework of bipartite entanglement. To this aim we first exploit rotationally invariant states as a test bed to detect genuine tripartite entanglement beyond the nearest neighbor in spin-1/2 models. Then we construct in a closed analytical form a family of entanglement witnesses which provides a sufficient condition to determine if a state of a many-body system formed by an arbitrary number of spin-1/2 particles possesses genuine tripartite entanglement, independently of the details of the model. We illustrate our method by analyzing in detail the anisotropic XXZ spin chain close to its phase transitions, where we demonstrate the presence of long-range multipartite entanglement near the critical point and the breaking of the symmetries associated with the quantum phase transition.}, issn = {1094-1622}, doi = {10.1103/PhysRevA.89.032330}, author = {Stasi{\'n}ska, J. and Rogers, B. and M. Paternostro and De Chiara, G. and Sanpera, A.} } @article {504, title = {{\textquoteleft}Pretty strong{\textquoteright} converse for the quantum capacity of degradable channels}, journal = {IEEE Transactions on Information Theory}, volume = {60}, number = {1}, year = {2014}, month = {01/2014}, pages = {317-333}, doi = {10.1109/TIT.2013.2288971}, author = {Ciara Morgan and Winter, Andreas} } @article {gendra_probabilistic_2014, title = {Probabilistic Metrology Attains Macroscopic Cloning of Quantum Clocks}, journal = {Physical Review Letters}, volume = {113}, number = {26}, year = {2014}, issn = {0031-9007, 1079-7114}, doi = {10.1103/PhysRevLett.113.260402}, url = {http://link.aps.org/doi/10.1103/PhysRevLett.113.260402}, author = {Gendra, B. and Calsamiglia, John and Mu{\~n}oz-Tapia, R. and E. Bagan and Chiribella, G.} } @article {523, title = {Quantum information: The occasional super clock-cloner}, journal = {Nature Physics}, volume = {10}, number = {2}, year = {2014}, month = {2/2014}, pages = {91}, issn = {1745-2473}, doi = {10.1038/nphys2853}, author = {Calsamiglia, John} } @article {688, title = {The Quantum Reverse Shannon Theorem and Resource Tradeoffs for Simulating Quantum Channels}, journal = {IEEE Transactions on Information Theory}, volume = {60}, number = {5}, year = {2014}, month = {5/2014}, pages = {2926-2959}, issn = {1557-9654}, doi = {10.1109/TIT.2014.2309968}, author = {Bennett, Charles H. and Devetak, Igor and Harrow, Aram W. and Shor, Peter W. and Winter, Andreas} } @article {piani_quantumness_2014, title = {Quantumness of correlations, quantumness of ensembles and quantum data hiding}, journal = {New Journal of Physics}, volume = {16}, number = {11}, year = {2014}, pages = {113001}, issn = {1367-2630}, doi = {10.1088/1367-2630/16/11/113001}, url = {http://stacks.iop.org/1367-2630/16/i=11/a=113001?key=crossref.9f5154f8c85e7f9471e2931d9a02df88}, author = {Piani, M and Narasimhachar, V and Calsamiglia, John} } @article {694, title = {Relative Entropy and Squashed Entanglement}, journal = {Communications in Mathematical Physics}, volume = {326}, number = {1}, year = {2014}, month = {2/2014}, pages = {63-80}, issn = {1432-0916}, doi = {10.1007/s00220-013-1871-2}, author = {Ke Li and Winter, Andreas} } @article {563, title = {Steering Bound Entangled States: A Counterexample to the Stronger Peres Conjecture}, journal = {Physical Review Letters}, volume = {113}, year = {2014}, month = {8/2014}, abstract = {Quantum correlations are at the heart of many applications in quantum information science and, at the same time, they form the basis for discussions about genuine quantum effects and their difference to classical physics. On one hand, entanglement theory provides the tools to quantify correlations in information processing and many results have been obtained to discriminate useful entanglement, which can be distilled to a pure form, from bound entanglement, being of limited use in many applications. On the other hand, for discriminating quantum phenomena from their classical counterparts, Schr\"odinger and Bell introduced the notions of steering and local hidden variable models. We provide a method to generate systematically bound entangled quantum states which can still be used for steering and therefore to rule out local hidden state models. This sheds light on the relations between the various views on quantum correlations and disproves a widespread conjecture known as the stronger Peres conjecture. For practical applications, it implies that even the weakest form of entanglement can be certified in a semi-device independent way.}, issn = {1079-7114}, doi = {10.1103/PhysRevLett.113.050404}, author = {Moroder, Tobias and Gittsovich, Oleg and Huber, Marcus and G{\"u}hne, Otfried} } @article {686, title = {Strong Converse for the Classical Capacity of Entanglement-Breaking and Hadamard Channels via a Sandwiched R{\'e}nyi Relative Entropy}, journal = {Communications in Mathematical Physics}, volume = {331}, number = {2}, year = {2014}, month = {10/2014}, pages = {593-622}, issn = {1432-0916}, doi = {10.1007/s00220-014-2122-x}, author = {Wilde, Mark M. and Winter, Andreas and Dong Yang} } @article {693, title = {Strong converse for the classical capacity of the pure-loss bosonic channel}, journal = {Problems of Information Transmission}, volume = {50}, number = {2}, year = {2014}, month = {4/2014}, pages = {117-132}, issn = {1608-3253}, doi = {10.1134/S003294601402001X}, author = {Wilde, Mark M. and Winter, Andreas} } @proceedings {697, title = {Strong Converse for the Quantum Capacity of the Erasure Channel for Almost All Codes}, volume = {27}, year = {2014}, pages = {52-66}, publisher = {LIPICS}, address = {Singapore}, doi = {10.4230/LIPIcs.TQC.2014.52}, author = {Wilde, Mark M. and Winter, Andreas}, editor = {Steve T Flammia and Harrow, Aram W.} } @article {564, title = {Unified approach to entanglement criteria using the Cauchy-Schwarz and H{\"o}lder inequalities}, journal = {Physical Review A}, volume = {90}, year = {2014}, month = {8/2014}, abstract = {We present a unified approach to different recent entanglement criteria. Although they were developed in different ways, we show that they are all applications of a more general principle given by the Cauchy-Schwarz inequality. We explain this general principle and show how to use it to derive not only already known entanglement criteria, but also criteria which were unknown so far. We systematically investigate its potential and limitations to detect bipartite and multipartite entanglement. Furthermore, we describe how to apply our generalized entanglement detection scheme to find the measurement directions to verify the entanglement of a given state experimentally.}, issn = {1094-1622}, doi = {10.1103/PhysRevA.90.022315}, author = {W{\"o}lk, Sabine and Huber, Marcus and G{\"u}hne, Otfried} } @article {683, title = {What does an experimental test of quantum contextuality prove or disprove?}, journal = {Journal of Physics A: Mathematical and Theoretical}, volume = {47}, number = {42}, year = {2014}, month = {10/2014}, pages = {424031}, issn = {1751-8121}, doi = {10.1088/1751-8113/47/42/424031}, author = {Winter, Andreas} } @article {562, title = {Witnessing Genuine Multipartite Entanglement with Positive Maps}, journal = {Physical Review Letters}, volume = {113}, year = {2014}, month = {9/2014}, abstract = {We derive a general framework that connects every positive map with a corresponding witness for partial separability in multipartite quantum systems. We show that many previous approaches were intimately connected to the witnesses derived from partial transposition and that such criteria can easily be outperformed in higher dimensions by non-decomposable maps. As an exemplary case we present a witness that is capable of detecting genuine multipartite entanglement in bound entangled states.}, issn = {1079-7114}, doi = {10.1103/PhysRevLett.113.100501}, author = {Huber, Marcus and Sengupta, Ritabrata} } @article {429, title = {Bose-Glass Phases of Ultracold Atoms due to Cavity Backaction}, journal = {Physical Review Letters}, volume = {110}, year = {2013}, month = {2/2013}, abstract = {We determine the quantum ground-state properties of ultracold bosonic atoms interacting with the mode of a high-finesse resonator. The atoms are confined by an external optical lattice, whose period is incommensurate with the cavity mode wavelength, and are driven by a transverse laser, which is resonant with the cavity mode. While for pointlike atoms photon scattering into the cavity is suppressed, for sufficiently strong lasers quantum fluctuations can support the buildup of an intracavity field, which in turn amplifies quantum fluctuations. The dynamics is described by a Bose-Hubbard model where the coefficients due to the cavity field depend on the atomic density at all lattice sites. Quantum Monte Carlo simulations and mean-field calculations show that, for large parameter regions, cavity backaction forces the atoms into clusters with a checkerboard density distribution. Here, the ground state lacks superfluidity and possesses finite compressibility, typical of a Bose glass. This system constitutes a novel setting where quantum fluctuations give rise to effects usually associated with disorder.}, issn = {1079-7114}, doi = {10.1103/PhysRevLett.110.075304}, url = {http://prl.aps.org/abstract/PRL/v110/i7/e075304}, author = {Hessam Habibian and Andr{\'e} Winter and Paganelli, Simone and Heiko Rieger and Giovanna Morigi} } @article {492, title = {Bound entanglement in the Jaynes{\textendash}Cummings model}, journal = {Journal of Physics B: Atomic, Molecular and Optical Physics}, volume = {46}, year = {2013}, month = {11/2013}, pages = {224002}, issn = {1361-6455}, doi = {10.1088/0953-4075/46/22/224002}, author = {Quesada, Nicol{\'a}s and Sanpera, Anna} } @article {494, title = {Decomposition of any quantum measurement into extremals}, journal = {Journal of Physics A: Mathematical and Theoretical}, volume = {46}, year = {2013}, month = {09/2013}, pages = {375302}, issn = {1751-8121}, doi = {10.1088/1751-8113/46/37/375302}, author = {Sent{\'\i}s, G and Gendra, B. and Bartlett, S D and Doherty, A C} } @article {503, title = {Distinguishing Multi-Partite States by Local Measurements}, journal = {Communications in Mathematical Physics}, volume = {323}, number = {2}, year = {2013}, month = {10/2013}, pages = {555 - 573}, issn = {1432-0916}, doi = {10.1007/s00220-013-1779-x}, author = {Lancien, C{\'e}cilia and Winter, Andreas} } @article {krenn_entangled_2013, title = {Entangled singularity patterns of photons in {Ince}-{Gauss} modes}, journal = {Physical Review A}, volume = {87}, number = {1}, year = {2013}, month = {jan}, issn = {1050-2947, 1094-1622}, doi = {10.1103/PhysRevA.87.012326}, url = {http://link.aps.org/doi/10.1103/PhysRevA.87.012326}, author = {Krenn, Mario and Robert Fickler and Huber, Marcus and Radek Lapkiewicz and Plick, William and Ramelow, Sven and Anton Zeilinger} } @article {570, title = {Entanglement Generation is Not Necessary for Optimal Work Extraction}, journal = {Physical Review Letters}, volume = {111}, year = {2013}, month = {12/2013}, abstract = {We consider reversible work extraction from identical quantum batteries. From an ensemble of individually passive states, work can be produced only via global unitary (and thus entangling) operations. However, we show here that there always exists a method to extract all possible work without creating any entanglement, at the price of generically requiring more operations (i.e. additional time). We then study faster methods to extract work and provide a quantitative relation between the amount of generated multipartite entanglement and extractable work. Our results suggest a general relation between entanglement generation and the power of work extraction.}, issn = {1079-7114}, doi = {10.1103/PhysRevLett.111.240401}, author = {Hovhannisyan, Karen and Mart{\'\i} Perarnau-Llobet and Huber, Marcus and Ac{\'\i}n, Antonio} } @article {515, title = {Entropy vector formalism and the structure of multidimensional entanglement in multipartite systems}, journal = {Physical Review A}, volume = {88}, year = {2013}, month = {10/2013}, issn = {1094-1622}, doi = {10.1103/PhysRevA.88.042328}, url = {http://arxiv.org/abs/1307.3541}, author = {Huber, Marcus and Mart{\'\i} Perarnau-Llobet and de Vicente, Julio I.} } @article {spengler_examining_2013, title = {Examining the dimensionality of genuine multipartite entanglement}, journal = {Quantum Information Processing}, volume = {12}, number = {1}, year = {2013}, pages = {269{\textendash}278}, issn = {1570-0755, 1573-1332}, doi = {10.1007/s11128-012-0369-8}, url = {http://link.springer.com/10.1007/s11128-012-0369-8}, author = {Spengler, Christoph and Huber, Marcus and Gabriel, Andreas and Hiesmayr, Beatrix C.} } @inbook {464, title = {Identification via Quantum Channels}, booktitle = {Information Theory, Combinatorics, and Search Theory: In Memory of Rudolf Ahlswede}, series = {Lecture Notes in Computer Science}, volume = {LNCS 7777}, year = {2013}, pages = {217 - 233}, publisher = {Springer Berlin Heidelberg}, organization = {Springer Berlin Heidelberg}, address = {Berlin, Heidelberg}, isbn = {978-3-642-36899-8}, issn = {1611-3349}, doi = {10.1007/978-3-642-36899-8_9}, author = {Winter, Andreas}, editor = {Aydinian, Harout and Cicalese, Ferdinando and Deppe, Christian} } @article {499, title = {Programmable discrimination with an error margin}, journal = {Physical Review A}, volume = {88}, year = {2013}, month = {11/2013}, pages = {052304}, issn = {1094-1622}, doi = {10.1103/PhysRevA.88.052304}, author = {Sent{\'\i}s, G and E. Bagan and Calsamiglia, John and Mu{\~n}oz-Tapia, R.} } @article {erdosi_proving_2013, title = {Proving the generation of genuine multipartite entanglement in a single-neutron interferometer experiment}, journal = {New Journal of Physics}, volume = {15}, number = {2}, year = {2013}, pages = {023033}, issn = {1367-2630}, doi = {10.1088/1367-2630/15/2/023033}, url = {http://stacks.iop.org/1367-2630/15/i=2/a=023033?key=crossref.b714f63bb49eb9e64ce9a70aa4a6ddfe}, author = {Erd{\"o}si, Daniel and Huber, Marcus and Hiesmayr, Beatrix C. and Hasegawa, Yuji} } @proceedings {505, title = {The Quantum Entropy Cone of Stabiliser States}, volume = {22}, number = {1302.5453}, year = {2013}, month = {02/2013}, pages = {270-284}, address = {Guelph, ON}, doi = {10.4230/LIPIcs.TQC.2013.270}, author = {Noah Linden and Frantisek Matus and Mary Beth Ruskai and Winter, Andreas}, editor = {Severini, Simone and Fernando Brandao} } @article {517, title = {Quantum hypergraph states}, journal = {New Journal of Physics}, volume = {15}, year = {2013}, month = {11/2013}, pages = {113022}, doi = {10.1088/1367-2630/15/11/113022}, author = {Rossi, M and Huber, M and Bru{\ss}, D. and Macchiavello, C.} } @article {436, title = {Quantum Metrology Assisted by Abstention}, journal = {Physical Review Letters}, volume = {110}, year = {2013}, month = {3/2013}, pages = {100501}, abstract = {The main goal of quantum metrology is to obtain accurate values of physical parameters using quantum probes. In this context, we show that abstention, i.e., the possibility of getting an inconclusive answer at readout, can drastically improve the measurement precision and even lead to a change in its asymptotic behavior, from the shot-noise to the Heisenberg scaling. We focus on phase estimation and quantify the required amount of abstention for a given precision. We also develop analytical tools to obtain the asymptotic behavior of the precision and required rate of abstention for arbitrary pure states.}, issn = {1079-7114}, doi = {10.1103/PhysRevLett.110.100501}, url = {http://prl.aps.org/abstract/PRL/v110/i10/e100501}, author = {Gendra, B. and Ronco-Bonvehi, E. and Calsamiglia, John and Mu{\~n}oz-Tapia, R. and E. Bagan} } @article {471, title = {Quantum phases of incommensurate optical lattices due to cavity backaction}, journal = {Phyiscal Review A}, volume = {88}, year = {2013}, pages = {043618}, author = {Hessam Habibian and Andr{\'e} Winter and Paganelli, Simone and Heiko Rieger and Giovanna Morigi} } @article {502, title = {Quantum Rate-Distortion Coding With Auxiliary Resources}, journal = {IEEE Transactions on Information Theory}, volume = {59}, number = {10}, year = {2013}, month = {10/2013}, pages = {6755 - 6773}, issn = {1557-9654}, doi = {10.1109/TIT.2013.2271772}, author = {Wilde, Mark M. and Datta, Nilanjana and Hsieh, Min-Hsiu and Winter, Andreas} } @article {507, title = {Quantum State Cloning Using Deutschian Closed Timelike Curves}, journal = {Physical Review Letters}, volume = {111}, number = {19}, year = {2013}, month = {11/2013}, pages = {190401}, issn = {1079-7114}, doi = {10.1103/PhysRevLett.111.190401}, author = {Brun, Todd A. and Wilde, Mark M. and Winter, Andreas} } @article {463, title = {Quantum-to-classical rate distortion coding}, journal = {Journal of Mathematical Physics}, volume = {54}, number = {4}, year = {2013}, month = {2013}, pages = {042201}, issn = {00222488}, doi = {10.1063/1.4798396}, author = {Datta, Nilanjana and Hsieh, Min-Hsiu and Wilde, Mark M. and Winter, Andreas} } @article {468, title = {Routing quantum information in spin chains}, journal = {Physical Review A}, volume = {87}, year = {2013}, month = {6/2013}, issn = {1094-1622}, doi = {10.1103/PhysRevA.87.062309}, author = {Paganelli, Simone and Lorenzo, Salvatore and Apollaro, Tony J. G. and Plastina, Francesco and Giorgi, Gian Luca} } @article {493, title = {Scaling of the entanglement spectrum near quantum phase transitions}, journal = {Physical Review B}, volume = {87}, year = {2013}, month = {6/2013}, issn = {1550-235X}, doi = {10.1103/PhysRevB.87.235107}, author = {Lepori, L. and De Chiara, G. and Sanpera, A.} } @article {442, title = {Structure of Multidimensional Entanglement in Multipartite Systems}, journal = {Physical Review Letters}, volume = {110}, year = {2013}, month = {1/2013}, abstract = {We explore the structure of multipartite quantum systems which are entangled in multiple degrees of freedom. We find necessary and sufficient conditions for the characterization of tripartite systems and necessary conditions for any number of parties. Furthermore we develop a framework of multilevel witnesses for efficient discrimination and quantification of multidimensional entanglement that is applicable for an arbitrary number of systems and dimensions.}, issn = {1079-7114}, doi = {10.1103/PhysRevLett.110.030501}, author = {Huber, Marcus and de Vicente, Julio I.} } @article {497, title = {The structure of Renyi entropic inequalities}, journal = {Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences}, volume = {469}, year = {2013}, month = {10/2013}, pages = {20120737 }, issn = {0018-9448}, doi = {10.1098/rspa.2012.0737}, author = {Linden, N. and Mosonyi, M. and Winter, A.} } @article {511, title = {Weak randomness in device-independent quantum key distribution and the advantage of using high-dimensional entanglement}, journal = {Physical Review A}, volume = {88}, year = {2013}, month = {9/2013}, issn = {1094-1622}, doi = {10.1103/PhysRevA.88.032309}, author = {Huber, Marcus and Paw{\l}owski, Marcin} } @article {462, title = {Zero-Error Communication via Quantum Channels, Noncommutative Graphs, and a Quantum Lov{\'a}sz Number}, journal = {IEEE Transactions on Information Theory}, volume = {59}, number = {2}, year = {2013}, month = {02/2013}, pages = {1164 - 1174}, issn = {1557-9654}, doi = {10.1109/TIT.2012.2221677}, author = {Duan, Runyao and Severini, Simone and Winter, Andreas} } @article {gendra_beating_2012, title = {Beating noise with abstention in state estimation}, journal = {New Journal of Physics}, volume = {14}, number = {10}, year = {2012}, pages = {105015}, issn = {1367-2630}, doi = {10.1088/1367-2630/14/10/105015}, url = {http://iopscience.iop.org/1367-2630/14/10/105015}, author = {Gendra, Bernat and Ronco-Bonvehi, Elio and Calsamiglia, John and Mu{\~n}oz-Tapia, Ramon and Bagan, Emilio} } @article {Stasinska2012, title = {Beyond pure state entanglement for atomic ensembles}, journal = {New Journal of Physics}, volume = {14}, number = {3}, year = {2012}, pages = {033034}, abstract = {We analyze multipartite entanglement between atomic ensembles within quantum matter{\textendash}light interfaces. In our proposal, a polarized light beam crosses sequentially several polarized atomic ensembles impinging on each of them at a given angle $\alpha$ i . These angles are crucial parameters for shaping the entanglement since they are directly connected to the appropriate combinations of the collective atomic spins that are squeezed. We exploit such a scheme to go beyond the pure state paradigm proposing realistic experimental settings to address multipartite mixed state entanglement in continuous variables.}, issn = {1367-2630}, doi = {10.1088/1367-2630/14/3/033034}, url = {http://stacks.iop.org/1367-2630/14/i=3/a=033034}, author = {Julia Stasi{\'n}ska and Paganelli, Simone and Sanpera, Anna} } @article {Stasinska_convergence, title = {Convergence of expansions in Schr{\"o}dinger and Dirac eigenfunctions, with an application to the R-matrix theory}, journal = {J. Math. Phys.}, volume = {53}, year = {2012}, pages = {022101}, doi = {10.1063/1.3679763}, url = {http://arxiv.org/pdf/0912.2909v3}, author = {Julia Stasi{\'n}ska} } @mastersthesis {391, title = {Entanglement distribution in quantum complex networks}, volume = {Doctorat en F{\'\i}sica}, year = {2012}, month = {11/2012}, school = {Universitat Aut{\`o}noma de Barcelona}, type = {PhD}, address = {Barcelona}, abstract = {This thesis deals with the study of quantum networks with a complex structure, the implications this structure has in the distribution of entanglement and how their functioning can be enhanced by operating in the quantum regime. We first consider a complex network of bipartite states, both pure and mixed, and study the distribution of long-distance entanglement. Then, we move to a network with noisy channels and study the creation and distribution of large, multipartite states. The work contained in this thesis is primarily motivated by the idea that the interplay between quantum information and complex networks may give rise to a new understanding and characterization of natural systems. Complex networks are of particular importance in communication infrastructures, as most present telecommunication networks have a complex structure. In the case of quantum networks, which are the necessary framework for distributed quantum processing and for quantum communication, it is very plausible that in the future they acquire a complex topology resembling that of existing networks, or even that methods will be developed to use current infrastructures in the quantum regime. A central task in quantum networks is to devise strategies to distribute entanglement among its nodes. In the first part of this thesis, we consider the distribution of bipartite entanglement as an entanglement percolation process in a complex network. Within this approach, perfect entanglement is established probabilistically between two arbitrary nodes. We see that for large networks, the probability of doing so is a constant strictly greater than zero (and independent of the size of the network) if the initial amount of entanglement is above a certain critical value. Quantum mechanics offer here the possibility to change the structure of the network without need to establish new, "physical" channels. By a proper local transformation of the network, the critical entanglement can be decreased and the probability increased. We apply this transformation to complex network models with arbitrary degree distribution. In the case of a noisy network of mixed states, we see that for some classes of states, the same approach of entanglement percolation can be used. For general mixed states, we consider a limited-path-length entanglement percolation constrained by the amount of noise in the connections. We see how complex networks still offer a great advantage in the probability of connecting two nodes. In the second part, we move to the multipartite scenario. We study the creation and distribution of graph states with a structure that mimic the underlying communication network. In this case, we use an arbitrary complex network of noisy channels, and consider that operations and measurements are also noisy. We propose an efficient scheme to distribute and purify small subgraphs, which are then merged to reproduce the desired state. We compare this approach with two bipartite protocols that rely on a central station and full knowledge of the network structure. We show that the fidelity of the generated graphs can be written as the partition function of a classical disordered spin system (a spin glass), and its decay rate is the analog of the free energy. Applying the three protocols to a one-dimensional network and to complex networks, we see that they are all comparable, and in some cases the proposed subgraph protocol, which needs only local information of the network, performs even better. }, author = {Cuquet, Mart{\'\i}} } @mastersthesis {390, title = {Entanglement percolation with graph-states{\textquoteright}}, volume = {Grau en F{\'\i}sica}, year = {2012}, month = {09/2012}, school = {Universitat Aut{\`o}noma de Barcelona}, type = {BSc Thesis}, address = {Barcelona}, author = {Franquet, Abert} } @article {443, title = {Entanglement Spectrum, Critical Exponents, and Order Parameters in Quantum Spin Chains}, journal = {Physical Review Letters}, volume = {109}, year = {2012}, month = {12/2012}, abstract = {We investigate the entanglement spectrum near criticality in finite quantum spin chains. Using finite size scaling we show that when approaching a quantum phase transition, the Schmidt gap, i.e., the difference between the two largest eigenvalues of the reduced density matrix λ1, λ2, signals the critical point and scales with universal critical exponents related to the relevant operators of the corresponding perturbed conformal field theory describing the critical point. Such scaling behavior allows us to identify explicitly the Schmidt gap as a local order parameter.}, issn = {1079-7114}, doi = {10.1103/PhysRevLett.109.237208}, author = {De Chiara, G. and Lepori, L. and Lewenstein, M. and Sanpera, A.} } @article {303, title = {From Vector Meson Dominance to Quark-Hadron Duality}, journal = {Il Nuovo Cimento}, volume = {35C}, year = {2012}, pages = {9-14}, abstract = {A short review of the many contributions to hadron physics made by Mario Greco is presented. The review roughly covers his production between1971 and 1974, just before the advent of QCD, when quark-model ideas, duality principles and vector meson dominance were widely accepted, developed and applied. The present author had the privilege to collaborate with Mario in most of these contributions and looking backward in time to remember the good old days we spent together in Frascati has been a great pleasure.}, doi = {10.1393/ncc/i2012-11133-9}, url = {http://arxiv.org/abs/1203.4205}, author = {Bramon, Albert} } @article {Stasinska2011, title = {Glass to superfluid transition in dirty bosons on a lattice}, journal = {New J. Phys.}, volume = {14}, year = {2012}, pages = {043043}, abstract = {We investigate the interplay between disorder and interactions in a Bose gas on a lattice in presence of randomly localized impurities. We compare the performance of two theoretical methods, the simple version of multi-orbital Hartree-Fock and the common Gross-Pitaevskii approach, showing how the former gives a very good approximation to the ground state in the limit of weak interactions, where the superfluid fraction is small. We further prove rigorously that for this class of disorder the fractal dimension of the ground state d* tends to the physical dimension in the thermodynamic limit. This allows us to introduce a quantity, the fractional occupation, which gives insightful information on the crossover from a Lifshits to a Bose glass. Finally, we compare temperature and interaction effects, highlighting similarities and intrinsic differences.}, doi = {10.1088/1367-2630/14/4/043043}, url = {http://arxiv.org/abs/1111.3494}, author = {Julia Stasi{\'n}ska and Massignan, Pietro and Bishop, Michael and Wehr, Jan and Sanpera, Anna and Lewenstein, Maciej} } @article {cuquet_growth_2012, title = {Growth of graph states in quantum networks}, journal = {Physical Review A}, volume = {86}, number = {4}, year = {2012}, pages = {042304}, abstract = {We propose a scheme to distribute graph states over quantum networks in the presence of noise in the channels and in the operations. The protocol can be implemented efficiently for large graph sates of arbitrary (complex) topology. We benchmark our scheme with two protocols where each connected component is prepared in a node belonging to the component and subsequently distributed via quantum repeaters to the remaining connected nodes. We show that the fidelity of the generated graphs can be written as the partition function of a classical Ising-type Hamiltonian. We give exact expressions of the fidelity of the linear cluster and results for its decay rate in random graphs with arbitrary (uncorrelated) degree distributions.}, doi = {10.1103/PhysRevA.86.042304}, url = {http://link.aps.org/doi/10.1103/PhysRevA.86.042304}, author = {Cuquet, Mart{\'\i} and Calsamiglia, John} } @article {Sentis:2012uq, title = {Quantum learning without quantum memory}, journal = {Scientific Reports (Nature Publishing Group)}, volume = {2}, year = {2012}, month = {10/2012}, pages = {708}, publisher = {Nature Publishing Group}, abstract = {A quantum learning machine for binary classification of qubit states that does not require quantum memory is introduced and shown to perform with the minimum error rate allowed by quantum mechanics for any size of the training set. This result is shown to be robust under (an arbitrary amount of) noise and under (statistical) variations in the composition of the training set, provided it is large enough. This machine can be used an arbitrary number of times without retraining. Its required classical memory grows only logarithmically with the number of training qubits, while its excess risk decreases as the inverse of this number, and twice as fast as the excess risk of an {\textquotedblleft}estimate-and-discriminate{\textquotedblright} machine, which estimates the states of the training qubits and classifies the data qubit with a discrimination protocol tailored to the obtained estimates.}, doi = {10.1038/srep00708}, url = {http://www.nature.com/srep/2012/121005/srep00708/full/srep00708.html}, author = {Sent{\'\i}s, Gael and Calsamiglia, John and Mu{\~n}oz-Tapia, Ramon and Bagan, Emilio} } @article {444, title = {Quantum Memory Assisted Probing of Dynamical Spin Correlations}, journal = {Physical Review Letters}, volume = {108}, year = {2012}, month = {2/2012}, abstract = {We propose a method to probe time-dependent correlations of nontrivial observables in many-body ultracold lattice gases. The scheme uses a quantum nondemolition matter-light interface, first to map the observable of interest on the many-body system into the light and then to store coherently such information into an external system acting as a quantum memory. Correlations of the observable at two (or more) instances of time are retrieved with a single final measurement that includes the readout of the quantum memory. Such a method brings to reach the study of dynamics of many-body systems in and out of equilibrium by means of quantum memories in the field of quantum simulators.}, issn = {1079-7114}, doi = {10.1103/PhysRevLett.108.065302}, author = {O. Romero-Isart and Rizzi, M. and Muschik, C. A. and Polzik, E. S. and Lewenstein, M. and Sanpera, A.} } @article {383, title = {Spin-driven spatial symmetry breaking of spinor condensates in a double well}, journal = {Physical Review A}, volume = {86}, year = {2012}, month = {2012/11/26/}, pages = {053626 - }, publisher = {American Physical Society}, url = {http://link.aps.org/doi/10.1103/PhysRevA.86.053626}, author = {Mel{\'e}-Messeguer, M. and Paganelli, Simone and Juli{\'a}-D{\'\i}az, B. and Ann Sanpera and Polls, A.} } @book {360, title = {Ultracold atoms in optical lattices: simulating Quantum Many-Body systems}, year = {2012}, publisher = {Oxford University Press}, organization = {Oxford University Press}, isbn = {978-0199573127}, issn = {0199573123}, author = {Lewenstein Maciej and Sanpera Anna and Ahufinger Ver{\`o}nica} } @article {PhysRevLett.106.220403, title = {All Nonclassical Correlations Can Be Activated into Distillable Entanglement}, journal = {Phys. Rev. Lett.}, volume = {106}, number = {22}, year = {2011}, month = {Jun}, pages = {220403}, publisher = {American Physical Society}, doi = {10.1103/PhysRevLett.106.220403}, url = {http://prl.aps.org/abstract/PRL/v106/i22/e220403}, author = {Piani, Marco and Gharibian, Sevag and Adesso, Gerardo and Calsamiglia, John and Horodecki, Pawe{\l} and Winter, Andreas} } @article {PhysRevLett.107.070401, title = {Bell Inequalities with No Quantum Violation and Unextendable Product Bases}, journal = {Phys. Rev. Lett.}, volume = {107}, number = {7}, year = {2011}, month = {Aug}, pages = {070401}, publisher = {American Physical Society}, abstract = {The strength of classical correlations is subject to certain constraints, commonly known as Bell inequalities. Violation of these inequalities is the manifestation of nonlocality{\textemdash}displayed, in particular, by quantum mechanics, meaning that quantum mechanics can outperform classical physics at tasks associated with such Bell inequalities. Interestingly, however, there exist situations in which this is not the case. We associate an intriguing class of bound entangled states, constructed from unextendable product bases with a wide family of tasks, for which (i) quantum correlations do not outperform the classical ones but (ii) there exist supraquantum nonsignaling correlations that do provide an advantage.}, doi = {10.1103/PhysRevLett.107.070401}, author = {Remigiusz Augusiak and Julia Stasi{\'n}ska and Hadley, Christopher and Korbicz, Jaros{\l}aw K. and Lewenstein, Maciej and Ac{\'\i}n, Antonio} } @article {428, title = {Bilinear-biquadratic spin-1 chain undergoing quadratic Zeeman effect}, journal = {Physical Review B}, volume = {84}, year = {2011}, month = {8/2011}, abstract = {The Heisenberg model for spin-1 bosons in one dimension presents many different quantum phases, including the famous topological Haldane phase. Here we study the robustness of such phases in front of a SU(2) symmetry-breaking field as well as the emergence of unique phases. Previous studies have analyzed the effect of such uniaxial anisotropy in some restricted relevant points of the phase diagram. Here we extend those studies and present the complete phase diagram of the spin-1 chain with uniaxial anisotropy. To this aim, we employ the density-matrix renormalization group together with analytical approaches. The complete phase diagram can be realized using ultracold spinor gases in the Mott insulator regime under a quadratic Zeeman effect.}, issn = {1550-235X}, doi = {10.1103/PhysRevB.84.054451}, url = {http://prb.aps.org/abstract/PRB/v84/i5/e054451}, author = {De Chiara, G. and Lewenstein, M. and Sanpera, A.} } @article {Gharibian:2011kq, title = {Characterizing quantumness via entanglement creation}, journal = {International Journal of Quantum Information}, volume = {9}, year = {2011}, month = {05}, pages = {1701-1713}, doi = {10.1142/S0219749911008258}, url = {http://arxiv.org/abs/1105.3419}, author = {Gharibian, Sevag and Piani, Marco and Adesso, Gerardo and Calsamiglia, John and Pawel Horodecki} } @article {2010arXiv1007.0403S, title = {A continuous-variable formalism for the Faraday atom-light interface}, journal = {ArXiv e-prints}, year = {2011}, abstract = {Quantum interfaces between polarized atomic ensembles and coherent states of light, applied recently to manipulate bipartite and multipartite entanglement, are revisited by means of a continuous-variable formalism. The explicit use of the continuous-variable formalism facilitates significantly the analysis of entanglement between different modes, reducing it to the study of the properties of a final covariance matrix which can be found analytically. Furthermore, it allows to study matter-light interfaces for mixed states, adapting the formalism to the experimental situations in which the initial prepared Gaussian states are, unavoidably, affected by a certain amount of noise. A multipartite scenario, leading to the generation of macroscopic cluster states is presented and analyzed in detail within this formalism.}, url = {http://arxiv.org/abs/1007.0403}, author = {Stasi{\'n}ska, J. and Paganelli, Simone and Rod{\'o}, C. and Sanpera, A.} } @article {430, title = {Detection of Entanglement in Ultracold Lattice Gases}, journal = {Journal of Low Temperature Physics}, volume = {165}, year = {2011}, month = {12/2011}, pages = {292 - 305}, abstract = {Probing non trivial magnetic ordering in quantum magnets realized with ultracold lattice gases demands detection methods with some spatial resolution built on it. Here we demonstrate that the Faraday matter-light interface provides an experimentally feasible tool to distinguish indubitably different quantum phases of a given many-body system in a non-demolishing way. We illustrate our approach by focussing on the Heisenberg chain for spin-1 bosons in the presence of a SU(2) symmetry breaking field. We explain how using the light signal obtained via homodyne detection one can reconstruct the phase diagram of the model. Further we show that the very same technique that provides a direct experimentally measurable signal of different order parameters can be extended to detect also the presence of multipartite entanglement in such systems.}, issn = {1573-7357}, doi = {10.1007/s10909-011-0403-8}, url = {link.springer.com/article/10.1007\%2Fs10909-011-0403-8}, author = {Chiara, G. and Sanpera, A.} } @article {2010arXiv1007.5177L, title = {Disordered spinor Bose-Hubbard model}, journal = {Phys. Rev. A}, volume = {83}, year = {2011}, pages = {013605}, abstract = {We study the zero-temperature phase diagram of the disordered spin-1 Bose-Hubbard model in a two-dimensional square lattice. To this aim, we use a mean-field Gutzwiller ansatz and a probabilistic mean-field perturbation theory. The spin interaction induces two different regimes, corresponding to a ferromagnetic and antiferromagnetic order. In the ferromagnetic case, the introduction of disorder reproduces analogous features of the disordered scalar Bose-Hubbard model, consisting in the formation of a Bose glass phase between Mott insulator lobes. In the antiferromagnetic regime, the phase diagram differs more from the scalar case. Disorder in the chemical potential can lead to the disappearance of Mott insulator lobes with an odd-integer filling factor and, for sufficiently strong spin coupling, to Bose glass of singlets between even-filling Mott insulator lobes. Disorder in the spinor coupling parameter results in the appearance of a Bose glass phase only between the n and the n+1 lobes for n odd. Disorder in the scalar Hubbard interaction inhibits Mott insulator regions for occupation larger than a critical value.}, keywords = {Condensed Matter - Other Condensed Matter, Quantum Physics}, doi = {10.1103/PhysRevA.83.013605}, url = {http://link.aps.org/doi/10.1103/PhysRevA.83.013605}, author = {{\L}{\k a}cki, M. and Paganelli, Simone and Ahufinger, V. and Sanpera, Anna and Zakrzewski, J.} } @article {330, title = {Entanglement detection in hybrid optomechanical systems}, journal = {Phys. Rev. A}, volume = {83}, year = {2011}, pages = {052324}, abstract = {We study a device formed by a Bose Einstein condensate (BEC) coupled to the field of a cavity with a moving end-mirror and find a working point such that the mirror-light entanglement is reproduced by the BEC-light quantum correlations. This provides an experimentally viable tool for inferring mirror-light entanglement with only a limited set of assumptions. We prove the existence of tripartite entanglement in the hybrid device, persisting up to temperatures of a few milli-Kelvin, and discuss a scheme to detect it. }, doi = {10.1103/PhysRevA.83.052324}, url = {http://link.aps.org/doi/10.1103/PhysRevA.83.052324}, author = {De Chiara, Gabriele and Paternostro, Mauro and Palma, G. Massimo} } @article {431, title = {Entangling two distant oscillators with a quantum reservoir}, journal = {EPL (Europhysics Letters)}, volume = {95}, year = {2011}, month = {09/2011}, pages = {60008}, abstract = {The generation of entanglement between two oscillators that interact via a common reservoir is theoretically studied. The reservoir is modeled by a one-dimensional harmonic crystal initially in thermal equilibrium. Starting from a separable state, the oscillators can become entangled after a transient time, that is of the order of the thermalization time scale. This behaviour is observed at finite temperature even when the oscillators are at a distance significantly larger than the crystal{\textquoteright}s interparticle spacing. The underlying physical mechanisms can be explained by the dynamical properties of the collective variables of the two oscillators which may decouple from or be squeezed by the reservoir. Our predictions can be tested with an ion chain in a linear Paul trap.}, issn = {1286-4854}, doi = {10.1209/0295-5075/95/60008}, url = {http://epljournal.edpsciences.org/index.php?option=com_article\&access=standard\&Itemid=129\&url=/articles/epl/abs/2011/18/epl13816/epl13816.html}, author = {Wolf, A and De Chiara, G. and Kajari, E and Lutz, E and G. Morigi} } @article {303, title = {Limited-path-length entanglement percolation in quantum complex networks}, journal = {Physical Review A}, volume = {83}, number = {3}, year = {2011}, month = {03/2011}, pages = {032319-14}, abstract = {We study entanglement distribution in quantum complex networks where nodes are connected by bipartite entangled states. These networks are characterized by a complex structure, which dramatically affects how information is transmitted through them. For pure quantum state links, quantum networks exhibit a remarkable feature absent in classical networks: it is possible to effectively rewire the network by performing local operations on the nodes. We propose a family of such quantum operations that decrease the entanglement percolation threshold of the network and increase the size of the giant connected component. We provide analytic results for complex networks with an arbitrary (uncorrelated) degree distribution. These results are in good agreement with numerical simulations, which also show enhancement in correlated and real-world networks. The proposed quantum preprocessing strategies are not robust in the presence of noise. However, even when the links consist of (noisy) mixed-state links, one can send quantum information through a connecting path with a fidelity that decreases with the path length. In this noisy scenario, complex networks offer a clear advantage over regular lattices, namely, the fact that two arbitrary nodes can be connected through a relatively small number of steps, known as the small-world effect. We calculate the probability that two arbitrary nodes in the network can successfully communicate with a fidelity above a given threshold. This amounts to working out the classical problem of percolation with a limited path length. We find that this probability can be significant even for paths limited to few connections and that the results for standard (unlimited) percolation are soon recovered if the path length exceeds by a finite amount the average path length, which in complex networks generally scales logarithmically with the size of the network.}, doi = {10.1103/PhysRevA.83.032319}, url = {http://pra.aps.org/abstract/PRA/v83/i3/e032319}, author = {Cuquet, Mart{\'\i} and Calsamiglia, John} } @article {292, title = {Probing magnetic order in ultracold lattice gases}, journal = {Phys. Rev. A }, volume = {83}, year = {2011}, pages = {021604}, abstract = {A forthcoming challenge in ultracold lattice gases is the simulation of quantum magnetism. That involves both the preparation of the lattice atomic gas in the desired spin state and the probing of the state. Here we demonstrate how a probing scheme based on atom-light interfaces gives access to the order parameters of nontrivial quantum magnetic phases, allowing us to characterize univocally strongly correlated magnetic systems produced in ultracold gases. This method, which is also nondemolishing, yields spatially resolved spin correlations and can be applied to bosons or fermions. As a proof of principle, we apply this method to detect the complete phase diagram displayed by a chain of (rotationally invariant) spin-1 bosons.}, doi = {10.1103/PhysRevA.83.021604}, url = {http://pra.aps.org/abstract/PRA/v83/i2/e021604}, author = {De Chiara, Gabriele and O. Romero-Isart and Sanpera, A.} } @article {432, title = {Quantifying, characterizing, and controlling information flow in ultracold atomic gases}, journal = {Physical Review A}, volume = {84}, year = {2011}, month = {9/2011}, abstract = {We study quantum information flow in a model comprised of a trapped impurity qubit immersed in a Bose-Einstein-condensed reservoir. We demonstrate how information flux between the qubit and the condensate can be manipulated by engineering the ultracold reservoir within experimentally realistic limits. We show that this system undergoes a transition from Markovian to non-Markovian dynamics, which can be controlled by changing key parameters such as the condensate scattering length. In this way, one can realize a quantum simulator of both Markovian and non-Markovian open quantum systems, the latter ones being characterized by a reverse flow of information from the background gas (reservoir) to the impurity (system).}, issn = {1094-1622}, doi = {10.1103/PhysRevA.84.031602}, url = {http://pra.aps.org/abstract/PRA/v84/i3/e031602}, author = {Haikka, P. and McEndoo, S. and De Chiara, G. and G. M. Palma and Maniscalco, S.} } @mastersthesis {392, title = {Quantum Accuracy Limits and Benchmarks in Continuos Variable Systems}, volume = {Doctorat en F{\'\i}sica}, year = {2011}, month = {10/2011}, school = {Universitat Aut{\`o}noma de Barcelona}, type = {PhD}, address = {Barcelona}, author = {Bracons, Mariona (formerly Mariona Aspachs)} } @article {345, title = {Spin Effects in Bose-Glass Phases}, journal = {J Low Temp Phys}, volume = {165}, year = {2011}, pages = {227}, doi = {10.1007/s10909-011-0392-7}, url = {http://www.springerlink.com/content/10w5036068935773/}, author = {Paganelli, Simone and {\L}a̧cki, Mateusz and Ahufinger, Veronica and Zakrzewski, Jakub and Sanpera, Anna} } @article {oreshkov_adiabatic_2010, title = {Adiabatic Markovian Dynamics}, journal = {Phys. Rev. Lett.}, volume = { 105}, year = {2010}, pages = {050503}, abstract = {We propose a theory of adiabaticity in quantum Markovian dynamics based on a structural decomposition of the Hilbert space induced by the asymptotic behavior of the Lindblad semigroup. A central idea of our approach is that the natural generalization of the concept of eigenspace of the Hamiltonian in the case of Markovian dynamics is a noiseless subsystem with a minimal noisy cofactor. Unlike previous attempts to define adiabaticity for open systems, our approach deals exclusively with physical entities and provides a simple, intuitive picture at the underlying Hilbert-space level, linking the notion of adiabaticity to the theory of noiseless subsystems. As an application of our theory, we propose a framework for decoherence-assisted computation in noiseless codes under general Markovian noise. We also formulate a dissipation-driven approach to holonomic computation based on adiabatic dragging of subsystems that is generally not achievable by non-dissipative means.}, keywords = {Quantum Physics}, doi = {10.1103/PhysRevLett.105.050503}, url = {http://arxiv.org/abs/1002.2219}, author = {Oreshkov, Ognyan and Calsamiglia, John} } @article {235, title = {Cold-atom induced control of an opto-mechanical device}, journal = {Phys. Rev. Lett.}, volume = {104}, year = {2010}, month = {06/2010}, pages = {243602}, abstract = {We consider a cavity with a vibrating end mirror and coupled to a Bose-Einstein condensate. The cavity field mediates the interplay between mirror and collective oscillations of the atomic density. We study the implications of this dynamics and the possibility of an indirect diagnostic. Our predictions can be observed in a realistic setup that is central to the current quest for mesoscopic quantumness.}, doi = {10.1103/PhysRevLett.104.243602}, url = { http://link.aps.org/doi/10.1103/PhysRevLett.104.243602}, author = {M. Paternostro and De Chiara, Gabriele and G. M. Palma} } @article {PhysRevA.81.031607, title = {Creating p-wave superfluids and topological excitations in optical lattices}, journal = {Phys. Rev. A}, volume = {81}, number = {3}, year = {2010}, month = {Mar/2010}, pages = {031607}, publisher = {American Physical Society}, abstract = {We propose to realize a p-wave superfluid using bosons mixed with a single species of fermions in a deep optical lattice. We analyze with a self-consistent method its excitation spectrum in presence of a vortex, and we point out the range of interaction strengths in which the zero-energy mode with topological character exists on a finite optical lattice. Lattice effects are strongest close to fermionic half filling: here the linearity of the low-lying spectrum is lost, and a new class of extended zero-energy modes with checkerboard structure and d-wave symmetry appears.}, doi = {10.1103/PhysRevA.81.031607}, url = {http://link.aps.org/doi/10.1103/PhysRevA.81.031607}, author = {Massignan, P. and Sanpera, A. and Lewenstein, M.} } @article {PhysRevLett.105.020403, title = {Decay of Polarons and Molecules in a Strongly Polarized Fermi Gas}, journal = {Phys. Rev. Lett.}, volume = {105}, number = {2}, year = {2010}, month = {Jul}, pages = {020403}, publisher = {American Physical Society}, abstract = {The ground state of an impurity immersed in a Fermi sea changes from a polaron to a molecule as the interaction strength is increased. We show here that the coupling between these two states is strongly suppressed due to a combination of phase-space effects and Fermi statistics, and that it vanishes much faster than the energy difference between the two states, thereby confirming the first order nature of the polaron-molecule transition. In the regime where each state is metastable, we find quasiparticle lifetimes which are much longer than what is expected for a usual Fermi liquid. Our analysis indicates that the decay rates are sufficiently slow to be experimentally observable.}, doi = {10.1103/PhysRevLett.105.020403}, url = {http://link.aps.org/doi/10.1103/PhysRevLett.105.020403}, author = {Bruun, G. M. and Massignan, P.} } @mastersthesis {295, title = {Discriminaci{\'o} qu{\`a}ntica}, volume = {Grau en F{\'\i}sica}, year = {2010}, month = {07/2010}, school = {Universitat Aut{\`o}noma de Barcelona}, type = {BSc Thesis}, address = {Barcelona}, abstract = {S{\textquoteright}estudia la discriminaci{\'o} de diferents sistemes qu{\`a}ntics. S{\textquoteright}analitza el proc{\'e}s de discriminaci{\'o} entre q{\'u}bits, i es compara amb la discriminaci{\'o} de mesures projectives. Seguidament, es busquen les condicions en les quals la discriminaci{\'o} entre mesures projectives {\'e}s perfecta, i es realitza el mateix per a la discriminaci{\'o} de transformacions unit{\`a}ries, per tal de comparar ambd{\'o}s resultats.}, author = {Arnau Pujol} } @article {de_vicente_estimation_2010, title = {Estimation of quantum finite mixtures}, journal = {Physical Review A}, volume = {81}, number = {1}, year = {2010}, month = {1/2010}, pages = {012332}, abstract = {We consider the problem of determining the weights of a quantum ensemble. That is to say, given a quantum system that is in a set of possible known states according to an unknown probability law, we give strategies to estimate the individual probabilities, weights, or mixing proportions. Such strategies can be used to estimate the frequencies at which different independent signals are emitted by a source. They can also be used to estimate the weights of particular terms in a canonical decomposition of a quantum channel. The quality of these strategies is quantified by a covariance-type error matrix. According with this cost function, we give optimal strategies in both the single-shot and multiple-copy scenarios. The latter is also analyzed in the asymptotic limit of large number of copies. We give closed expressions of the error matrix for two-component quantum mixtures of qubit systems. The Fisher information plays an unusual role in the problem at hand, providing exact expressions of the minimum covariance matrix for any number of copies.}, doi = {10.1103/PhysRevA.81.012332}, url = {http://link.aps.org/doi/10.1103/PhysRevA.81.012332}, author = {de Vicente, J. I. and Calsamiglia, John and Mu{\~n}oz-Tapia, Ramon and Bagan, Emilio} } @article {giorgi2010, title = {Ion-trap simulation of the quantum phase transition in an exactly solvable model of spins coupled to bosons}, journal = {Phys. Rev. A}, volume = {81}, year = {2010}, month = {2010}, pages = {052118}, abstract = {It is known that arrays of trapped ions can be used to efficiently simulate a variety of many-body quantum systems. Here we show how it is possible to build a model representing a spin chain interacting with bosons that is exactly solvable. The exact spectrum of the model at zero temperature and the ground-state properties are studied. We show that a quantum phase transition occurs when the coupling between spins and bosons reaches a critical value, which corresponds to a level crossing in the energy spectrum. Once the critical point is reached, the number of bosonic excitations in the ground state, which can be assumed as an order parameter, starts to be different from zero. The population of the bosonic mode is accompanied by a macroscopic magnetization of the spins. This double effect could represent a useful resource for phase transition detection since a measure of the phonon can give information about the phase of the spin system. A finite-temperature phase diagram is also given in the adiabatic regime.}, keywords = {Quantum Physics}, doi = {10.1103/PhysRevA.81.052118}, author = {Giorgi, Gian Luca and Paganelli, Simone and Galve, Fernando} } @article {PhysRevLett.105.080504, title = {Local Discrimination of Mixed States}, journal = {Phys. Rev. Lett.}, volume = {105}, number = {8}, year = {2010}, month = {Aug}, pages = {080504}, publisher = {American Physical Society}, doi = {10.1103/PhysRevLett.105.080504}, author = {Calsamiglia, John and de Vicente, J. I. and Mu{\~n}oz-Tapia, R. and E. Bagan} } @mastersthesis {293, title = {Localitat i separabilitat en discriminaci{\'o} d{\textquoteright}hip{\`o}tesis qu{\`a}ntiques}, volume = {Grau en F{\'\i}sica}, year = {2010}, month = {07/2010}, school = {Universitat Aut{\`o}noma de Barcelona}, type = {BSc Thesis}, address = {Barcelona}, abstract = {En aquest treball s{\textquoteright}estudiar{\`a} la probabilitat {\`o}ptima d{\textquoteright}obtenir l{\textquoteright}estat correcte en una mesura sobre un sistema de N c{\`o}pies de tres estats qu{\`a}ntics amb probabilitats a priori id{\`e}ntiques i separats 120{\textordmasculine}. S{\textquoteright}estudiaran diferents estrat{\`e}gies, posant especial {\`e}mfasi en la localitat i l{\textquoteright}entrella{\c c}ament de les mesures. Finalment es far{\`a} una generalitzaci{\'o} d{\textquoteright}aquestes estrat{\`e}gies per a estats mescla, estudiant la probabilitat de discriminar-los en funci{\'o} de la seva puresa i l{\textquoteright}estrat{\`e}gia portada a terme.}, author = {Caminal Armadans, Roger} } @mastersthesis {298, title = {Localitzaci{\'o} en xarxes complexes}, volume = {Grau en F{\'\i}sica}, year = {2010}, month = {07/2010}, school = {Universitat Aut{\`o}noma de Barcelona}, type = {BSc Thesis}, address = {Barcelona}, abstract = {En els anys 1950s, P.W. Anderson va suggerir la possibilitat d{\textquoteright}un nou fenomen en f{\'\i}sica de l{\textquoteright}estat s{\`o}lid: la localitzaci{\'o}. Aquest fenomen consisteix en que la funci{\'o} d{\textquoteright}ona dels electrons es queda totalment localitzada en l{\textquoteright}espai provocant que el material passi de ser un conductor a un a{\"\i}llant. Ha estat extensament estudiat en xarxes ordenades i {\'e}s conseq{\"u}{\`e}ncia de les impureses del material. En aquest treball, pretenem estudiar la localitzaci{\'o} en xarxes amb naturalesa aleat{\`o}ria, en particular, en xarxes complexes. La idea b{\`a}sica {\'e}s, tenint en compte que l{\textquoteright}aleatorietat de les impureses del material provoca localitzaci{\'o}, veure si l{\textquoteright}aleatorietat en l{\textquoteright}estructura del material produeix el mateix efecte.}, author = {Perarnau Llobet, Mart{\'\i}} } @article {sentis_multicopy_2010, title = {Multicopy programmable discrimination of general qubit states}, journal = {Physical Review A}, volume = {82}, number = {4}, year = {2010}, month = {10/2010}, pages = {042312}, abstract = {Quantum state discrimination is a fundamental primitive in quantum statistics where one has to correctly identify the state of a system that is in one of two possible known states. A programmable discrimination machine performs this task when the pair of possible states is not a priori known but instead the two possible states are provided through two respective program ports. We study optimal programmable discrimination machines for general qubit states when several copies of states are available in the data or program ports. Two scenarios are considered: One in which the purity of the possible states is a priori known, and the fully universal one where the machine operates over generic mixed states of unknown purity. We find analytical results for both the unambiguous and minimum error discrimination strategies. This allows us to calculate the asymptotic performance of programmable discrimination machines when a large number of copies are provided and to recover the standard state discrimination and state comparison values as different limiting cases.}, doi = {10.1103/PhysRevA.82.042312}, url = {http://link.aps.org/doi/10.1103/PhysRevA.82.042312}, author = {Sent{\'\i}s, Gael and Bagan, Emili and Calsamiglia, John and Mu{\~n}oz-Tapia, Ramon} } @article {218, title = {The quantum ground state of self-organized atomic crystals in optical resonators}, journal = {Phys. Rev. A}, volume = {81}, year = {2010}, month = {04/2010}, pages = {043407}, abstract = {Cold atoms, driven by a laser and simultaneously coupled to the quantum field of an optical resonator, may self-organize in periodic structures. These structures are supported by the optical lattice, which emerges from the laser light they scatter into the cavity mode and form when the laser intensity exceeds a threshold value. We study theoretically the quantum ground state of these structures above the pump threshold of self-organization by mapping the atomic dynamics of the self-organized crystal to a Bose-Hubbard model. We find that the quantum ground state of the self-organized structure can be the one of a Mott insulator, depending on the pump strength of the driving laser. For very large pump strengths, where the intracavity-field intensity is maximum and one would expect a Mott-insulator state, we find intervals of parameters where the phase is compressible. These states could be realized in existing experimental setups.}, doi = {10.1103/PhysRevA.81.043407}, url = {http://link.aps.org/doi/10.1103/PhysRevA.81.043407}, author = {S. Fern{\'a}ndez-Vidal and De Chiara, Gabriele and J. Larson and G. Morigi} } @mastersthesis {294, title = {Quantum Information with continuous variable systems}, volume = {PhD}, year = {2010}, month = {04/2010}, school = {Universitat Aut{\`o}noma de Barcelona}, type = {PhD Thesis}, address = {Barcelona}, abstract = {This thesis deals with the study of quantum communication protocols with Continuous Variable (CV) systems. CV systems are those described by canonical conjugated coordinates $x$ and $p$ endowed with infinite dimensional Hilbert spaces, thus involving a complex mathematical structure. A special class of CV states, are the so-called Gaussian states. We present a protocol that permits to extract quantum keys from entangled Gaussian states. Differently from discrete systems, Gaussian entangled states cannot be distilled with Gaussian operations only. However it was already shown, that it is still possible to extract perfectly correlated classical bits to establish secret random keys. We properly modify the protocol using bipartite Gaussian entanglement to perform quantum key distribution in an efficient and realistic way. We describe and demonstrate security in front of different possible attacks on the communication, detailing the resources demanded. We also consider a simple 3-partite protocol known as Byzantine Agreement. It is an old classical communication problem in which parties (with possible traitors among them) can only communicate pairwise, while trying to reach a common decision. Classically, there is a bound in the maximal number of possible traitors that can be involved in the game. Nevertheless, a quantum solution exist. We show that solution within CV using multipartite entangled Gaussian states and Gaussian operations. Furthermore, we show under which premises concerning entanglement content of the state, noise, inefficient homodyne detectors, our protocol is efficient and applicable with present technology. It is known that in spite of their exceptional role within the space of all CV states, in fact, Gaussian states are not always the best candidates to perform quantum information tasks. Thus, we tackle the problem of quantification of correlations (quantum and/or classical) between two CV modes (Gaussian and non-Gaussian). We propose to define correlations between the two modes as the maximal number of correlated bits extracted via local quadrature measurements on each mode. On Gaussian states, where entanglement is accessible via their covariance matrix our quantification majorizes entanglement, reducing to an entanglement monotone for pure states. For non-Gaussian states, such as photonic Bell states, photon subtracted states and mixtures of Gaussian states, the bit quadrature correlations are shown to be also a monotonic function of the negativity. This quantification yields a feasible, operational way to measure non-Gaussian entanglement in current experiments by means of direct homodyne detection, without needing a complete state tomography with the same complexity as if dealing with Gaussian states. Finally we focus to atomic ensembles described as CV. Measurement induced entanglement between two macroscopical atomic samples was reported experimentally in 2001. There, the interaction between a single laser pulse propagating through two spatially separated atomic samples combined with a final projective measurement on the light led to the creation of pure EPR entanglement between the two samples. We show how to generate, manipulate and detect mesoscopic entanglement between an arbitrary number of atomic samples through a quantum non-demolition matter-light interface. Our proposal extends in a non-trivial way for multipartite entanglement (GHZ and cluster-like) without needing local magnetic fields. Moreover, we show quite surprisingly that given the irreversible character of a measurement, the interaction of the atomic sample with a second pulse light can modify and even reverse the entangling action of the first one leaving the samples in a separable state.}, author = {Rod{\'o}, Carles} } @article {rapcan_recycling_2010, title = {Recycling of qubits}, journal = {Physica Scripta}, volume = {T140}, year = {2010}, pages = {014059}, abstract = {We consider a finite number, N, of qubits that encode a pure single qubit state SU(2) covariantly. Given the N-qubit state has already been measured optimally to estimate the single-qubit state, we analyse the maximum information obtainable by a second, and subsequent observers ignorant of important details of the previous measurements. We quantify the information acquired by each observer as a function of N and of the number of independent observers that in succession have independently measured the same ensemble of qubits before him.}, issn = {0031-8949}, doi = {10.1088/0031-8949/2010/T140/014059}, url = {http://iopscience.iop.org/1402-4896/2010/T140/014059?fromSearchPage=true}, author = {P Rapcan and Calsamiglia, John and Mu{\~n}oz-Tapia, Ramon and Bagan, Emilio and V Buzek} } @article {288, title = {Spontaneous nucleation of structural defects in inhomogeneous ion chains}, journal = {New. J. Phys.}, volume = {12}, year = {2010}, month = {12/2010}, pages = {115003}, abstract = {Structural defects in ion crystals can be formed during a linear quench of the transverse trapping frequency across the mechanical instability from a linear chain to the zigzag structure. The density of defects after the sweep can be conveniently described by the Kibble-Zurek mechanism. In particular, the number of kinks in the zigzag ordering can be derived from a time-dependent Ginzburg-Landau equation for the order parameter, here the zigzag transverse size, under the assumption that the ions are continuously laser cooled. In a linear Paul trap the transition becomes inhomogeneous, being the charge density larger in the center and more rarefied at the edges. During the linear quench the mechanical instability is first crossed in the center of the chain, and a front, at which the mechanical instability is crossed during the quench, is identified which propagates along the chain from the center to the edges. If the velocity of this front is smaller than the sound velocity, the dynamics becomes adiabatic even in the thermodynamic limit and no defect is produced. Otherwise, the nucleation of kinks is reduced with respect to the case in which the charges are homogeneously distributed, leading to a new scaling of the density of kinks with the quenching rate. The analytical predictions are verified numerically by integrating the Langevin equations of motion of the ions, in presence of a time-dependent transverse confinement. We argue that the non-equilibrium dynamics of an ion chain in a Paul trap constitutes an ideal scenario to test the inhomogeneous extension of the Kibble-Zurek mechanism, which lacks experimental evidence to date. }, doi = {10.1088/1367-2630/12/11/115003}, url = {http://iopscience.iop.org/1367-2630/12/11/115003?fromSearchPage=true}, author = {De Chiara, Gabriele and del Campo, Adolfo and G. Morigi and M. B. Plenio and A. Retzker} } @article {220, title = {Structural defects in ion crystals by quenching the external potential: the inhomogeneous Kibble-Zurek mechanism}, journal = {Phys. Rev. Lett.}, volume = {105}, year = {2010}, month = {08/2010}, pages = {075701}, doi = {10.1103/PhysRevLett.105.075701}, url = {http://link.aps.org/doi/10.1103/PhysRevLett.105.075701}, author = {del Campo, Adolfo and De Chiara, Gabriele and G. Morigi and M. B. Plenio and A. Retzker} } @article {302, title = {Topological superfluids on a lattice with non-Abelian gauge fields}, journal = {Europhysics Letters}, volume = {92}, number = {4}, year = {2010}, month = {12/2010}, pages = {46004}, doi = {10.1209/0295-5075/92/46004}, url = {http://arxiv.org/abs/1007.4827}, author = {A. Kubasiak and Massignan, P. and Lewenstein, M.} } @article {Oreshkov2009c, title = {Comment on {\textquotedblleft}Nongeometric Conditional Phase Shift via Adiabatic Evolution of Dark Eigenstates: A New Approach to Quantum Computation{\textquotedblright}}, journal = {Physical Review Letters}, volume = {103}, number = {18}, year = {2009}, pages = {188901}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.103.188901}, url = {http://prl.aps.org/abstract/PRL/v103/i18/e188901}, author = {Oreshkov, Ognyan and Calsamiglia, John} } @article {Oreshkov2009, title = {Distinguishability measures between ensembles of quantum states}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {79}, number = {3}, year = {2009}, pages = {032336{\textendash}29}, issn = {1050-2947}, doi = {10.1103/PhysRevA.79.032336}, url = {http://link.aps.org/doi/10.1103/PhysRevA.79.032336}, author = {Oreshkov, Ognyan and Calsamiglia, John} } @article {Cuquet2009, title = {Entanglement Percolation in Quantum Complex Networks}, journal = {Physical Review Letters}, volume = {103}, number = {24}, year = {2009}, month = {12/2009}, pages = {240503{\textendash}4}, publisher = {APS}, abstract = {Quantum networks are essential to quantum information distributed applications, and communicatingover them is a key challenge. Complex networks have richand intriguing properties, which are as yet unexplored in thequantum setting. Here, we study the effect of entanglement percolationas a means to establish long-distance entanglement between arbitrary nodesof quantum complex networks. We develop a theory to analyticallystudy random graphs with arbitrary degree distribution and give exactresults for some models. Our findings are in good agreementwith numerical simulations and show that the proposed quantum strategiesenhance the percolation threshold substantially. Simulations also show a clearenhancement in small-world and other real-world networks.}, keywords = {complex networks, entanglement distribution, entanglement percolation, erdos-renyi, generating function, quantum complex networks, quantum networks, scale-free, small-world}, doi = {10.1103/PhysRevLett.103.240503}, url = {http://link.aps.org/abstract/PRL/v103/e240503}, author = {Cuquet, Mart{\'\i} and Calsamiglia, John} } @article {Oreshkov2009a, title = {Holonomic Quantum Computation in Subsystems}, journal = {Physical Review Letters}, volume = {103}, number = {9}, year = {2009}, pages = {090502}, abstract = {We introduce a generalized method of holonomic quantum computation (HQC) based on encoding in subsystems. As an application, we propose a scheme for applying holonomic gates to unencoded qubits by the use of a noisy ancillary qubit. This scheme does not require initialization in a subspace since all dynamical effects factor out as a transformation on the ancilla. We use this approach to show how fault-tolerant HQC can be realized via 2-local Hamiltonians with perturbative gadgets.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.103.090502}, url = {http://prl.aps.org/abstract/PRL/v103/i9/e090502}, author = {Oreshkov, Ognyan} } @article {Rodo2009, title = {Manipulating mesoscopic multipartite entanglement with atom-light interfaces}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {80}, number = {6}, year = {2009}, month = {12/2009}, pages = {062304{\textendash}8}, publisher = {APS}, abstract = {Entanglementbetween two macroscopic atomic ensembles induced by measurement on anancillary light system has proven to be a powerful methodfor engineering quantum memories and quantum state transfer. Here weinvestigate the feasibility of such methods for generation, manipulation, anddetection of genuine multipartite entanglement (Greenberger-Horne-Zeilinger and clusterlike states) betweenmesoscopic atomic ensembles without the need of individual addressing ofthe samples. Our results extend in a nontrivial way theEinstein-Podolsky-Rosen entanglement between two macroscopic gas samples reported experimentally in[B. Julsgaard, A. Kozhekin, and E. Polzik, Nature (London) 413,400 (2001)]. We find that under realistic conditions, a secondorthogonal light pulse interacting with the atomic samples, can modifyand even reverse the entangling action of the first oneleaving the samples in a separable state. {\textcopyright}2009 The American Physical Society}, keywords = {atom-photon collisions, EPR paradox, measurement theory, mesoscopic entanglement, multipartite entanglement, quantum entanglement, quantum optics}, url = {http://link.aps.org/abstract/PRA/v80/e062304}, author = {Julia Stasi{\'n}ska and Rod{\'o}, Carles and Paganelli, Simone and Sanpera, Anna and Birkl, G.} } @article {Paganelli2009, title = {Optimized electron propagation on a quantum chain by a topological phase}, journal = {Fortschritte der Physik}, volume = {57}, number = {11-12}, year = {2009}, pages = {1094{\textendash}1102}, abstract = {We study the quantum diffusion of an electron in a quantum chain starting from an initial state localized around a given site. As the wavepacket diffuses, the probability of reconstructing the initial state on another site diminishes drastically with the distance. In order to optimize the state transmission we find that a topological quantum phase can be introduced. The effect of this phase is the reduction of wavepacket spreading together with almost coherent group propagation. In this regime, the electron has a quasi-linear dispersion and high fidelity can be achieved also over large distances in terms of lattice spacing.}, issn = {00158208}, doi = {10.1002/prop.200900087}, url = {http://doi.wiley.com/10.1002/prop.200900087}, author = {Paganelli, Simone and Giorgi, G. L. and de Pasquale, F.} } @article {Aspachs2009, title = {Phase estimation for thermal Gaussian states}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {79}, number = {3}, year = {2009}, month = {03/2009}, pages = {033834{\textendash}12}, keywords = {gaussian noise, gaussian states, optical losses, optical squeezing, phase estimation, quantum noise, thermal noise}, doi = {10.1103/PhysRevA.79.033834}, url = {http://link.aps.org/abstract/PRA/v79/e033834}, author = {Aspachs, Mariona and Calsamiglia, John and Mu{\~n}oz-Tapia, Ramon and Bagan, Emili} } @article {Calsamiglia2009, title = {Phase-covariant quantum benchmarks}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {79}, number = {5}, year = {2009}, pages = {050301{\textendash}4}, keywords = {quantum benchmarks}, issn = {1050-2947}, doi = {10.1103/PhysRevA.79.050301}, url = {http://link.aps.org/doi/10.1103/PhysRevA.79.050301}, author = {Calsamiglia, John and Aspachs, Mariona and Mu{\~n}oz-Tapia, Ramon and Bagan, Emili} } @article {Augusiak2009_NJP, title = {Positive maps, majorization, entropic inequalities and detection of entanglement}, journal = {New Journal of Physics}, volume = {11}, number = {5}, year = {2009}, month = {05/2009}, pages = {053018}, doi = {10.1088/1367-2630/11/5/053018}, url = {http://stacks.iop.org/1367-2630/11/i=5/a=053018}, author = {Remigiusz Augusiak and Julia Stasi{\'n}ska} } @article {Jiang2009, title = {Preparation of decoherence-free cluster states with optical superlattices}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {79}, number = {2}, year = {2009}, month = {02/2009}, pages = {022309{\textendash}16}, keywords = {atom-photon collisions, ground states, optical multilayers, quantum optics, superlattices}, doi = {10.1103/PhysRevA.79.022309}, url = {http://link.aps.org/abstract/PRA/v79/e022309 http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal\&id=PLRAAN000079000002022309000001\&idtype=cvips\&gifs=yes http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf\&id=PLRAAN000079000002}, author = {Jiang, Liang and Rey, Ana Maria and Romero-Isart, Oriol and Garcia-Ripoll, Juan Jose and Sanpera, Anna and Lukin, Mikhail D.} } @article {Oreshkov2009b, title = {Scheme for fault-tolerant holonomic computation on stabilizer codes}, journal = {Physical Review A}, volume = {80}, number = {2}, year = {2009}, pages = {022325}, issn = {1050-2947}, doi = {10.1103/PhysRevA.80.022325}, url = {http://pra.aps.org/abstract/PRA/v80/i2/e022325}, author = {Oreshkov, Ognyan and Brun, Todd and Lidar, Daniel} } @article {Ahufinger2008, title = {Double-barrier potentials for matter-wave gap solitons}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {78}, number = {1}, year = {2008}, month = {07/2008}, pages = {013608{\textendash}5}, keywords = {Bose-Einstein condensation, Fabry-Perot interferometers, matter waves, optical solitons}, doi = {10.1103/PhysRevA.78.013608}, url = {http://link.aps.org/abstract/PRA/v78/e013608 http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal\&id=PLRAAN000078000001013608000001\&idtype=cvips\&gifs=yes}, author = {Ahufinger, Veronica and Malomed, B. A. and Birkl, G. and Corbal{\'a}n, Ramon and Sanpera, Anna} } @article {SenDe2008, title = {Frustration, Area Law, and Interference in Quantum Spin Models}, journal = {Physical Review Letters}, volume = {101}, number = {18}, year = {2008}, month = {10/2008}, pages = {187202{\textendash}4}, doi = {10.1103/PhysRevLett.101.187202}, url = {http://link.aps.org/abstract/PRL/v101/e187202}, author = {Sen(De), Aditi and Sen, Ujjwal and Dziarmaga, Jacek and Sanpera, Anna and Lewenstein, Maciej} } @article {Calvo2008, title = {Manipulation of single-photon states encoded in transverse spatial modes: Possible and impossible tasks}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {77}, number = {1}, year = {2008}, month = {01/2008}, pages = {012302{\textendash}7}, abstract = {Controlled generation and manipulation of photon states encoded in their spatial degrees of freedom is a crucial ingredient in many quantum-information tasks exploiting higher-than-two dimensional encoding. Here, we prove the impossibility to arbitrarily modify d-level state superpositions (qudits) for d>2, encoded in the transverse modes of light, with optical components associated to the group of symplectic transforms (Gaussian operations). Surprisingly, we also provide an explicit construction of how non-Gaussian operations acting on mode subspaces do enable one to overcome the limit d=2. In addition, this set of operations realizes the full SU(3) algebra.}, keywords = {SU(3) theory}, doi = {10.1103/PhysRevA.77.012302}, url = {http://link.aps.org/doi/10.1103/PhysRevA.77.012302}, author = {Calvo, Gabriel F. and Picon, Antonio} } @article {Calvo2008a, title = {Measuring the Complete Transverse Spatial Mode Spectrum of a Wave Field}, journal = {Physical Review Letters}, volume = {100}, number = {17}, year = {2008}, month = {05/2008}, pages = {173902{\textendash}4}, doi = {10.1103/PhysRevLett.100.173902}, url = {http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf\&id=PRLTAO000100000017173902000001\&idtype=cvips\&prog=normal}, author = {Calvo, Gabriel F. and Picon, Antonio and Zambrini, Roberta} } @article {Neigovzen2008, title = {Multipartite continuous-variable solution for the Byzantine agreement problem}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {77}, number = {6}, year = {2008}, month = {06/2008}, pages = {062307{\textendash}11}, keywords = {Gaussian processes, homodyne detection, quantum cryptography, quantum entanglement}, doi = {10.1103/PhysRevA.77.062307}, url = {http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf\&id=PLRAAN000077000006062307000001\&idtype=cvips\&prog=normal}, author = {Neigovzen, Rodion and Rod{\'o}, Carles and Adesso, Gerardo and Sanpera, Anna} } @article {Boixo2008a, title = {Operational Interpretation for Global Multipartite Entanglement}, journal = {Physical Review Letters}, volume = {100}, number = {10}, year = {2008}, month = {03/2008}, pages = {100503{\textendash}4}, keywords = {multipartite entanglement}, doi = {10.1103/PhysRevLett.100.100503}, url = {http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf\&id=PRLTAO000100000010100503000001\&idtype=cvips\&prog=normal http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal\&id=PRLTAO000100000010100503000001\&idtype=cvips\&gifs=yes http://}, author = {Boixo, Sergio and Monras, Alex} } @article {Rodo2008, title = {Operational Quantification of Continuous-Variable Correlations}, journal = {Physical Review Letters}, volume = {100}, number = {11}, year = {2008}, month = {03/2008}, pages = {110505{\textendash}4}, doi = {10.1103/PhysRevLett.100.110505}, url = {http://link.aps.org/abstract/PRL/v100/e110505}, author = {Rod{\'o}, Carles and Adesso, Gerardo and Sanpera, Anna} } @article {Oreshkov2008, title = {Operator quantum error correction for continuous dynamics}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {78}, number = {2}, year = {2008}, pages = {022333{\textendash}10}, keywords = {error correction codes, quantum noise}, doi = {10.1103/PhysRevA.78.022333}, url = {http://link.aps.org/abstract/PRA/v78/e022333}, author = {Oreshkov, Ognyan and Lidar, Daniel A. and Brun, Todd A.} } @article {Bagan2008, title = {Phase variance of squeezed vacuum states}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {78}, number = {4}, year = {2008}, month = {10/2008}, pages = {043829{\textendash}7}, keywords = {optical squeezing}, doi = {10.1103/PhysRevA.78.043829}, url = {http://link.aps.org/abstract/PRA/v78/e043829}, author = {Bagan, Emili and Monras, Alex and Mu{\~n}oz-Tapia, Ramon} } @article {Lewenstein2008, title = {Probing Quantum Magnetism with Cold Atoms}, journal = {Science}, volume = {319}, number = {5861}, year = {2008}, month = {01/2008}, pages = {292{\textendash}293}, doi = {10.1126/science.1153723}, url = {http://www.sciencemag.org/cgi/content/full/319/5861/292?maxtoshow=\&HITS=10\&hits=10\&RESULTFORMAT=\&fulltext=probing+quantum+magnetism\&searchid=1\&FIRSTINDEX=0\&resourcetype=HWCIT}, author = {Lewenstein, Maciej and Sanpera, Anna} } @article {Calsamiglia2008, title = {Quantum Chernoff bound as a measure of distinguishability between density matrices: Application to qubit and Gaussian states}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {77}, number = {3}, year = {2008}, month = {03/2008}, pages = {032311{\textendash}15}, keywords = {Bayes methods, error statistics, quantum chernoff bound, quantum statistical mechanics, quantum theory}, doi = {10.1103/PhysRevA.77.032311}, url = {http://link.aps.org/abstract/PRA/v77/e032311}, author = {Calsamiglia, John and Mu{\~n}oz-Tapia, Ramon and Masanes, Llu{\'\i}s and Ac{\'\i}n, Antonio and Bagan, Emili} } @article {Monras2008, title = {Quantum information processing in spin chains via quantum Zeno dynamics}, journal = {arXiv}, year = {2008}, month = {01/2008}, abstract = {We show how the quantum Zeno effect can be exploited to control quantum information in a spin chain in a flexible way. In particular, we consider a one dimensional array of three level systems interacting via a swap operator, an interaction found in a generalized Heisenberg Hamiltonian. By encoding the qubit into two levels and using simple projective frequent measurements, the dynamics of the chain is guided to achieve basic quantum information manipulation tools, $\backslash$emph\{i.e.\}, quantum registers, single qubit operations and quantum state transfer on demand, while local addressability is not required. State transfer is perfect, robust against errors and delivers qubits at a constant rate, unconditional of the length of the transfer. Moreover, two dimensional lattices with tunable global interactions in different directions offer the possibility of performing two-qubit gates.}, keywords = {spin chain}, url = {http://arxiv.org/abs/0801.1959}, author = {Monras, Alex and Romero-Isart, Oriol} } @article {Eckert2008, title = {Quantum non-demolition detection of strongly correlated systems}, journal = {Nature Physics}, volume = {4}, number = {1}, year = {2008}, month = {01/2008}, pages = {50{\textendash}54}, issn = {1745-2473}, doi = {10.1038/nphys776}, url = {http://www.nature.com/nphys/journal/v4/n1/full/nphys776.html}, author = {Eckert, Kai and Romero-Isart, Oriol and Rodriguez, Mirta and Lewenstein, Maciej and Polzik, Eugene S. and Sanpera, Anna} } @article {Boixo2008, title = {Quantum-limited metrology with product states}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {77}, number = {1}, year = {2008}, month = {01/2008}, pages = {012317{\textendash}15}, keywords = {angular momentum theory, Bose-Einstein condensation, bound states, protocols, quantum entanglement}, doi = {10.1103/PhysRevA.77.012317}, url = {http://link.aps.org/abstract/PRA/v77/e012317}, author = {Boixo, Sergio and Datta, Animesh and Flammia, Steven T. and Shaji, Anil and Bagan, Emili and Caves, Carlton M.} } @article {audenaert_discriminating_2007, title = {Discriminating States: The Quantum Chernoff Bound}, journal = {Physical Review Letters}, volume = {98}, number = {16}, year = {2007}, pages = {160501{\textendash}4}, doi = {10.1103/PhysRevLett.98.160501}, url = {http://link.aps.org/abstract/PRL/v98/e160501}, author = {K. M. R. Audenaert and J. Calsamiglia and R. {Munoz-Tapia} and E. Bagan and Ll. Masanes and A. Acin and F. Verstraete} } @article {Audenaert2007, title = {Discriminating States: The Quantum Chernoff Bound}, journal = {Physical Review Letters}, volume = {98}, number = {16}, year = {2007}, month = {04/2007}, pages = {160501{\textendash}4}, keywords = {quantum chernoff bound, state discrimination}, doi = {10.1103/PhysRevLett.98.160501}, url = {http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal\&id=PRLTAO000098000016160501000001\&idtype=cvips\&gifs=yes}, author = {K. M. R. Audenaert and Calsamiglia, John and Mu{\~n}oz-Tapia, Ramon and Bagan, Emili and Masanes, Llu{\'\i}s and Ac{\'\i}n, Antonio and Verstraete, Frank} } @article {Rodo2007, title = {Efficiency in Quantum Key Distribution Protocols with Entangled Gaussian States}, journal = {Open Systems \& Information Dynamics}, volume = {14}, number = {1}, year = {2007}, month = {03/2007}, pages = {69{\textendash}80}, abstract = {Abstract Quantum key distribution (QKD) refers to specific quantum strategies which permit the secure distribution of a secret key between two parties that wish to communicate secretly. Quantum cryptography has proven unconditionally secure in ideal scenarios and has been successfully implemented using quantum states with finite (discrete) as well as infinite (continuous) degrees of freedom. Here, we analyze the efficiency of QKD protocols that use as a resource entangled gaussian states and gaussian operations only. In this framework, it has already been shown that QKD is possible [1] but the issue of its efficiency has not been considered. We propose a figure of merit (the efficiency E) to quantify the number of classical correlated bits that can be used to distill a key from a sample of N entangled states. We relate the efficiency of the protocol to the entanglement and purity of the states shared between the parties.}, keywords = {gaussian states, quantum cryptography, quantum key distribution}, doi = {10.1007/s11080-007-9030-x}, url = {http://dx.doi.org/10.1007/s11080-007-9030-x}, author = {Rod{\'o}, Carles and Romero-Isart, Oriol and Eckert, Kai and Sanpera, Anna} } @article {Eckert2007, title = {Efficient quantum-state transfer in spin chains via adiabatic passage}, journal = {New Journal of Physics}, volume = {9}, year = {2007}, pages = {155}, keywords = {spin chain, state transfer}, url = {http://iopscience.iop.org/1367-2630/9/5/155/pdf/1367-2630\_9\_5\_155.pdf}, author = {Eckert, Kai and Romero-Isart, Oriol and Sanpera, Anna} } @article {Bagan2007, title = {How to hide a secret direction}, journal = {New Journal of Physics}, volume = {9}, year = {2007}, pages = {244}, abstract = {We present a procedure to share a secret spatial direction in the absence of a common reference frame using a multipartite quantum state. The procedure guarantees that the parties can determine the direction if they perform joint measurements on the state, but fail to do so if they restrict themselves to local operations and classical communication (LOCC). We calculate the fidelity for joint measurements, give bounds on the fidelity achievable by LOCC, and prove that there is a non-vanishing gap between the two of them, even in the limit of infinitely many copies. The robustness of the procedure under particle loss is also studied. As a by-product we find bounds on the probability of discriminating by LOCC between the invariant subspaces of total angular momentum N/2 and N/2-1 in a system of N elementary spins.}, doi = {doi:10.1088/1367-2630/9/8/244}, url = {http://iopscience.iop.org/1367-2630/9/8/244/pdf/1367-2630\_9\_8\_244.pdf}, author = {Bagan, Emili and Calsamiglia, John and Demkowicz-Dobrzanski, R. and Mu{\~n}oz-Tapia, Ramon} } @conference {Bramon2007a, title = {Kaonic Quantitative Complementarity and Quantum Erasers}, booktitle = {AIP Conference Proceedings}, volume = {962}, year = {2007}, pages = {242}, url = {http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal\&id=APCPCS000962000001000242000001\&idtype=cvips\&gifs=yes}, author = {Bramon, Albert and Garbarino, G. and Hiesmayr, B. C.} } @article {Calvo2007a, title = {Measuring two-photon orbital angular momentum entanglement}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {75}, number = {1}, year = {2007}, month = {01/2007}, pages = {012319{\textendash}8}, keywords = {orbital angular momentum, quantum entanglement, quantum optics}, doi = {10.1103/PhysRevA.75.012319}, url = {http://link.aps.org/abstract/PRA/v75/e012319}, author = {Calvo, Gabriel F. and Picon, Antonio and Bramon, Albert} } @article {Monras2007, title = {Optimal Quantum Estimation of Loss in Bosonic Channels}, journal = {Physical Review Letters}, volume = {98}, number = {16}, year = {2007}, month = {04/2007}, pages = {160401{\textendash}4}, doi = {10.1103/PhysRevLett.98.160401}, url = {http://link.aps.org/abstract/PRL/v98/e160401}, author = {Monras, Alex and Paris, Matteo G. A.} } @article {Moreno-Cardoner2007, title = {Predicting Spinor Condensate Dynamics from Simple Principles}, journal = {Physical Review Letters}, volume = {99}, number = {2}, year = {2007}, month = {07/2007}, pages = {020404{\textendash}4}, keywords = {Bose-Einstein condensation, entropy}, doi = {10.1103/PhysRevLett.99.020404}, url = {http://link.aps.org/abstract/PRL/v99/e020404}, author = {Moreno-Cardoner, M. and Mur-Petit, J. and Guilleumas, M. and Polls, Artur and Sanpera, Anna and Lewenstein, Maciej} } @article {Bramon2007, title = {Quantum Mechanics with Neutral Kaons}, journal = {Acta Physica Polonica B}, volume = {38}, year = {2007}, pages = {2763{\textendash}2776}, url = {http://arxiv.org/abs/hep-ph/0703152}, author = {Bramon, Albert and Garbarino, G. and Hiesmayr, B. C.} } @article {Eckert2007b, title = {Quantum Polarization Spectroscopy of Ultracold Spinor Gases}, journal = {Physical Review Letters}, volume = {98}, number = {10}, year = {2007}, month = {03/2007}, pages = {100404{\textendash}4}, doi = {10.1103/PhysRevLett.98.100404}, url = {http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf\&id=PRLTAO000098000010100404000001\&idtype=cvips\&prog=normal}, author = {Eckert, Kai and Zawitkowski, L. and Sanpera, Anna and Lewenstein, Maciej and Polzik, Eugene S.} } @article {Romero-Isart2007b, title = {Quantum ratchets for quantum communication with optical superlattices}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {76}, number = {5}, year = {2007}, month = {11/2007}, pages = {052304{\textendash}8}, keywords = {atom-photon collisions, optical modulation, quantum entanglement, quantum optics, superlattices}, doi = {10.1103/PhysRevA.76.052304}, url = {http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf\&id=PLRAAN000076000005052304000001\&idtype=cvips\&prog=normal}, author = {Romero-Isart, Oriol and Garcia-Ripoll, Juan Jose} } @article {Romero-Isart2007a, title = {Quantum state transfer in spin-1 chains}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {75}, number = {5}, year = {2007}, month = {05/2007}, pages = {050303{\textendash}4}, keywords = {ferromagnetic materials, ground states, Heisenberg model, magnetic transitions, quantum entanglement, spin chain, spin systems, state transfer}, doi = {10.1103/PhysRevA.75.050303}, url = {http://link.aps.org/abstract/PRA/v75/e050303}, author = {Romero-Isart, Oriol and Eckert, Kai and Sanpera, Anna} } @article {Ahufinger2007, title = {Quantum switches and quantum memories for matter-wave lattice solitons}, journal = {New Journal of Physics}, volume = {9}, number = {1}, year = {2007}, pages = {4}, url = {http://iopscience.iop.org/1367-2630/9/1/004/pdf/1367-2630\_9\_1\_004.pdf}, author = {Ahufinger, Veronica and Mebrahtu, A. and Corbal{\'a}n, Ramon and Sanpera, Anna} } @article {Rapcan2007, title = {Recycling of quantum information: Multiple observations of quantum systems}, journal = {arXiv}, year = {2007}, month = {08/2007}, abstract = {Given a finite number of copies of an unknown qubit state that have already been measured optimally, can one still extract any information about the original unknown state? We give a positive answer to this question and quantify the information obtainable by a given observer as a function of the number of copies in the ensemble, and of the number of independent observers that, one after the other, have independently measured the same ensemble of qubits before him. The optimality of the protocol is proven and extensions to other states and encodings are also studied. According to the general lore, the state after a measurement has no information about the state before the measurement. Our results manifestly show that this statement has to be taken with a grain of salt, specially in situations where the quantum states encode confidential information.}, url = {http://arxiv.org/abs/0708.1086}, author = {Rapcan, Peter and Calsamiglia, John and Mu{\~n}oz-Tapia, Ramon and Bagan, Emili and Bu{\.z}ek, Vladimir} } @article {Calvo2007, title = {Spin-induced angular momentum switching}, journal = {Optics Letters}, volume = {32}, number = {7}, year = {2007}, month = {04/2007}, pages = {838{\textendash}840}, abstract = {When light is transmitted through optically inhomogeneous and anisotropic media the spatial distribution of light can be modified according to its input polarization state. A complete analysis of this process, based on the paraxial approximation, is presented, and we show how it can be exploited to produce a spin-controlled change in the orbital angular momentum of light beams propagating in patterned space-variant optical axis phase plates. We also unveil a new effect: the development of a strong modulation in the angular momentum change upon variation of the optical path through the phase plates.}, keywords = {angular momentum, anisotropic optical materials, polarization, polarization-selective devices, quantum optics}, doi = {10.1364/OL.32.000838}, url = {http://ol.osa.org/abstract.cfm?URI=ol-32-7-838}, author = {Calvo, Gabriel F. and Picon, Antonio} } @article {Romero-Isart2007, title = {Transport and entanglement generation in the Bose-Hubbard model}, journal = {Journal of Physics A: Mathematical and General}, volume = {40}, number = {28}, year = {2007}, pages = {8019{\textendash}8032}, url = {http://www.iop.org/EJ/article/1751-8121/40/28/S11/a7\_28\_s11.pdf}, author = {Romero-Isart, Oriol and Eckert, Kai and Rod{\'o}, Carles and Sanpera, Anna} } @article {Pons2007, title = {Trapped Ion Chain as a Neural Network: Error Resistant Quantum Computation}, journal = {Physical Review Letters}, volume = {98}, number = {2}, year = {2007}, month = {01/2007}, pages = {023003{\textendash}4}, keywords = {neural networks, quantum computation}, doi = {10.1103/PhysRevLett.98.023003}, url = {http://link.aps.org/abstract/PRL/v98/e023003}, author = {Pons, Marisa and Ahufinger, Veronica and Wunderlich, Christof and Sanpera, Anna and Braungardt, Sibylle and Sen(De), Aditi and Sen, Ujjwal and Lewenstein, Maciej} } @article {Eckert2007a, title = {Ultracold atomic Bose and Fermi spinor gases in optical lattices}, journal = {New Journal of Physics}, volume = {9}, year = {2007}, pages = {133}, keywords = {optical lattices}, url = {http://iopscience.iop.org/1367-2630/9/5/133/pdf/1367-2630\_9\_5\_133.pdf}, author = {Eckert, Kai and Zawitkowski, L. and Leskinen, M. J. and Sanpera, Anna and Lewenstein, Maciej} } @article {Lewenstein2007, title = {Ultracold atomic gases in optical lattices: mimicking condensed matter physics and beyond}, journal = {Advances in Physics}, volume = {56}, year = {2007}, pages = {243}, keywords = {optical lattices}, url = {http://www.informaworld.com/smpp/ftinterface\~content=a778175433\~fulltext=713240930}, author = {Lewenstein, Maciej and Sanpera, Anna and Ahufinger, Veronica and Damski, B. and Sen(De), Aditi and Sen, Ujjwal} } @article {Hartmann2007, title = {Weighted graph states and applications to spin chains, lattices and gases}, journal = {Journal of Physics B: Atomic, Molecular and Optical Physics}, volume = {40}, number = {9}, year = {2007}, pages = {S1}, doi = {10.1088/0953-4075/40/9/S01}, url = {http://www.iop.org/EJ/abstract/0953-4075/40/9/S01}, author = {Hartmann, L. and Calsamiglia, John and D{\"u}r, Wolfgang and Briegel, Hans J.} } @article {Bagan2006c, title = {Aligning spatial frames through quantum channels}, journal = {International Journal of Quantum Information}, volume = {4}, year = {2006}, pages = {5}, author = {Bagan, Emili and Mu{\~n}oz-Tapia, Ramon} } @article {Bramon2006, title = {Bell{\textquoteright}s Inequality Tests with Meson{\textendash}Antimeson Pairs}, journal = {Foundations of Physics}, volume = {36}, number = {4}, year = {2006}, month = {04/2006}, pages = {563{\textendash}584}, abstract = {Recent proposals to test Bell{\textquoteright}s inequalities with entangled pairs of pseudoscalar mesons are reviewed. This includes pairs of neutral kaons or B-mesons and offers some hope to close both the locality and the detection loopholes. Specific difficulties, however, appear thus invalidating most of those proposals. The best option requires the use of kaon regeneration effects and could lead to a successful test if moderate K0 and k̄0 detection efficiencies are achieved.}, keywords = {bell inequalities}, doi = {10.1007/s10701-005-9030-z}, url = {http://www.springerlink.com/content/2028326rqh24qgk6/fulltext.pdf}, author = {Bramon, Albert and Escribano, Rafel and Garbarino, G.} } @article {Mur-Petit2006, title = {Dynamics of F = 1 [sup 87]Rb condensates at finite temperatures}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {73}, number = {1}, year = {2006}, month = {01/2006}, pages = {013629{\textendash}6}, keywords = {atom optics, atom-photon collisions, Bose-Einstein condensation, radiation pressure, rubidium, spin dynamics, vectors}, doi = {10.1103/PhysRevA.73.013629}, url = {http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal\&id=PLRAAN000073000001013629000001\&idtype=cvips\&gifs=yes}, author = {Mur-Petit, J. and Guilleumas, M. and Polls, Artur and Sanpera, Anna and Lewenstein, Maciej and Bongs, K. and Sengstock, K.} } @article {Bramon2006a, title = {Kaonic Quantum Erasers at KLOE 2: "Erasing the Present, changing the Past{\textquoteright}{\textquoteright}}, journal = {arXiv}, year = {2006}, month = {11/2006}, abstract = {Neutral kaons are unique quantum systems to show some of the most puzzling peculiarities of quantum mechanics. Here we focus on a quantitative version of Bohr{\textquoteright}s complementary principle and on quantum marking and eraser concepts. In detail we show that neutral kaons (1) are kind of double slit devices encapsulating Bohr{\textquoteright}s complementarity principle in a simple and transparent way, and (2) offer marking and eraser options which are not afforded by other quantum systems and which can be performed at the DAPHNE machine.}, keywords = {Quantum Physics}, url = {http://www.arxiv.org/pdf/hep-ph/0609314.pdf http://arxiv.org/abs/hep-ph/0609314}, author = {Bramon, Albert and Garbarino, G. and Hiesmayr, B. H} } @article {Bagan2006, title = {Optimal full estimation of qubit mixed states}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {73}, number = {3}, year = {2006}, month = {03/2006}, pages = {032301{\textendash}18}, keywords = {mixed states, probability, state estimation}, doi = {10.1103/PhysRevA.73.032301}, url = {http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal\&id=PLRAAN000073000003032301000001\&idtype=cvips\&gifs=yes}, author = {Bagan, Emili and Ballester, M. A. and Gill, R. D. and Monras, Alex and Mu{\~n}oz-Tapia, Ramon} } @article {Monras2006, title = {Optimal phase measurements with pure Gaussian states}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {73}, number = {3}, year = {2006}, month = {03/2006}, pages = {033821{\textendash}8}, keywords = {gaussian states, optical squeezing, optical tomography, quantum theory}, doi = {10.1103/PhysRevA.73.033821}, url = {http://scitation.aip.org/vsearch/servlet/VerityServlet?KEY=ALL\&possible1=Monras\%2C+Alex\&possible1zone=author\&maxdisp=25\&smode=strresults\&aqs=true}, author = {Monras, Alex} } @article {Calvo2006, title = {Quantum field theory of photons with orbital angular momentum}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {73}, number = {1}, year = {2006}, month = {01/2006}, pages = {013805{\textendash}10}, keywords = {information theory, orbital angular momentum, quantum field theory, quantum optics}, doi = {10.1103/PhysRevA.73.013805}, url = {http://link.aps.org/abstract/PRA/v73/e013805}, author = {Calvo, Gabriel F. and Picon, Antonio and Bagan, Emili} } @article {SenDe2006, title = {Quantum-information processing in disordered and complex quantum systems}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {74}, number = {6}, year = {2006}, month = {12/2006}, pages = {062309{\textendash}8}, keywords = {information theory, quantum entanglement, quantum gates, radiation pressure}, doi = {10.1103/PhysRevA.74.062309}, url = {http://link.aps.org/abstract/PRA/v74/e062309}, author = {Sen(De), Aditi and Sen, Ujjwal and Ahufinger, Veronica and Briegel, Hans J. and Sanpera, Anna and Lewenstein, Maciej} } @article {Bagan2006b, title = {Relative states, quantum axes, and quantum references}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {73}, number = {2}, year = {2006}, month = {02/2006}, pages = {022341{\textendash}6}, keywords = {quantum theory}, doi = {10.1103/PhysRevA.73.022341}, url = {http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal\&id=PLRAAN000073000002022341000001\&idtype=cvips\&gifs=yes}, author = {Bagan, Emili and Iblisdir, Sofyan and Mu{\~n}oz-Tapia, Ramon} } @article {Acin2006, title = {Secrecy properties of quantum channels}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {73}, number = {1}, year = {2006}, month = {01/2006}, pages = {012327{\textendash}5}, keywords = {information theory, protocols, quantum cryptography}, doi = {10.1103/PhysRevA.73.012327}, url = {http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal\&id=PLRAAN000073000001012327000001\&idtype=cvips\&gifs=yes}, author = {Ac{\'\i}n, Antonio and Bae, J. and Bagan, Emili and Baig, Mari{\`a} and Masanes, Llu{\'\i}s and Mu{\~n}oz-Tapia, Ramon} } @article {Bagan2006a, title = {Separable Measurement Estimation of Density Matrices and its Fidelity Gap with Collective Protocols}, journal = {Physical Review Letters}, volume = {97}, number = {13}, year = {2006}, pages = {130501{\textendash}4}, keywords = {mixed states, state estimation}, doi = {10.1103/PhysRevLett.97.130501}, url = {http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal\&id=PRLTAO000097000013130501000001\&idtype=cvips\&gifs=yes}, author = {Bagan, Emili and Ballester, M. A. and Gill, R. D. and Mu{\~n}oz-Tapia, Ramon and Romero-Isart, Oriol} } @article {Mebrahtu2006, title = {Splitting and merging an elongated Bose-Einstein condensate at finite temperature}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {73}, number = {3}, year = {2006}, month = {03/2006}, pages = {033601{\textendash}7}, keywords = {Bose-Einstein condensation, critical points, fluctuations}, doi = {10.1103/PhysRevA.73.033601}, url = {http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal\&id=PLRAAN000073000003033601000001\&idtype=cvips\&gifs=yes}, author = {Mebrahtu, A. and Sanpera, Anna and Lewenstein, Maciej} } @article {Sanchez-Palencia2006, title = {Strongly correlated Fermi-Bose mixtures in disordered optical lattices}, journal = {JOURNAL OF PHYSICS-LONDON-B ATOMIC MOLECULAR AND OPTICAL PHYSICS}, volume = {39}, number = {10}, year = {2006}, pages = {121}, keywords = {optical lattices}, url = {http://iopscience.iop.org/0953-4075/39/10/S12/pdf/0953-4075\_39\_10\_S12.pdf}, author = {Sanchez-Palencia, L. and Ahufinger, Veronica and Kantian, A. and Zakrzewski, J. and Sanpera, Anna and Lewenstein, Maciej} } @article {Hulpke2006, title = {Unitarity as Preservation of Entropy and Entanglement in Quantum Systems}, journal = {Foundations of Physics}, volume = {36}, number = {4}, year = {2006}, month = {04/2006}, pages = {477{\textendash}499}, abstract = {Abstract The logical structure of Quantum Mechanics (QM) and its relation to other fundamental principles of Nature has been for decades a subject of intensive research. In particular, the question whether the dynamical axiom of QM can be derived from other principles has been often considered. In this contribution, we show that unitary evolutions arise as a consequences of demanding preservation of entropy in the evolution of a single pure quantum system, and preservation of entanglement in the evolution of composite quantum systems. 6}, doi = {10.1007/s10701-005-9035-7}, url = {http://www.springerlink.com/content/tjg6r668u462848r/fulltext.pdf}, author = {Hulpke, Florian and Poulsen, Uffe and Sanpera, Anna and Sen(De), Aditi and Sen, Ujjwal and Lewenstein, Maciej} } @article {Bramon2005a, title = {Bell{\textquoteright}s inequality tests: from photons to B-mesons}, journal = {Journal of Modern Optics}, volume = {52}, number = {12}, year = {2005}, pages = {1681{\textendash}1684}, doi = {10.1080/09500340500072893}, url = {http://dx.doi.org/10.1080/09500340500072893}, author = {Bramon, Albert and Escribano, Rafel and Garbarino, G.} } @article {Osterloh2005, title = {Cold Atoms in Non-Abelian Gauge Potentials: From the Hofstadter "Moth" to Lattice Gauge Theory}, journal = {Physical Review Letters}, volume = {95}, number = {1}, year = {2005}, month = {06/2005}, pages = {010403}, publisher = {American Physical Society}, abstract = {We demonstrate how to create artificial external non-Abelian gauge potentials acting on cold atoms in optical lattices. The method employs atoms with k internal states, and laser assisted state sensitive tunneling, described by unitary k{\texttimes}k matrices. The single-particle dynamics in the case of intense U(2) vector potentials lead to a generalized Hofstadter butterfly spectrum which shows a complex mothlike structure. We discuss the possibility to realize non-Abelian interferometry (Aharonov-Bohm effect) and to study many-body dynamics of ultracold matter in external lattice gauge fields.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.95.010403}, url = {http://link.aps.org/doi/10.1103/PhysRevLett.95.010403}, author = {Osterloh, K. and Baig, Mari{\`a} and Santos, L. and Zoller, P. and Lewenstein, Maciej} } @article {Bagan2005a, title = {Comprehensive analysis of quantum pure-state estimation for two-level systems}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {71}, number = {6}, year = {2005}, month = {06/2005}, pages = {062318}, publisher = {American Physical Society}, abstract = {Given N identical copies of the state of a quantum two-level system, we analyze its optimal estimation. We consider two situations: general pure states and (pure) states restricted to lie on the equator of the Bloch sphere. We perform a complete and comprehensive analysis of the optimal schemes based on local measurements, and give results (optimal measurements, maximum fidelity, etc.) for arbitrary N, not necessarily large, within the Bayesian framework. We also make a comparative analysis of the asymptotic limit of these results with those derived from a (pointwise) Cram{\'e}r-Rao type of approach. We give explicit schemes based on local measurements and no classical communication that saturate the fidelity bounds of the most general collective schemes.}, issn = {1050-2947}, doi = {10.1103/PhysRevA.71.062318}, url = {http://link.aps.org/doi/10.1103/PhysRevA.71.062318}, author = {Bagan, Emili and Monras, Alex and Mu{\~n}oz-Tapia, Ramon} } @article {Neigovzen2005, title = {Continuous Variable Solution for Byzantine Agreement}, journal = {arXiv}, year = {2005}, url = {http://arxiv.org/abs/quant-ph/0507249}, author = {Neigovzen, Rodion and Sanpera, Anna} } @conference {SenDe2005, title = {Disordered complex systems using cold gases and trapped ions}, booktitle = {Laser Spectroscopy: Proceedings of the XVII International Conference, Aviemore, Scotland UK, 19-24 June 2005}, year = {2005}, pages = {158{\textendash}166}, publisher = {World Scientific}, organization = {World Scientific}, address = {Singapore}, url = {http://arxiv.org/abs/quant-ph/0508018}, author = {Sen(De), Aditi and Sen, Ujjwal and Lewenstein, Maciej and Ahufinger, Veronica and Pons, Marisa and Sanpera, Anna}, editor = {Hinds, E. A. and Ferguson, A. and Riis, E.} } @article {Ahufinger2005, title = {Disordered ultracold atomic gases in optical lattices: A case study of Fermi-Bose mixtures}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {72}, number = {6}, year = {2005}, month = {12/2005}, pages = {063616}, publisher = {American Physical Society}, abstract = {We present a review of properties of ultracold atomic Fermi-Bose mixtures in inhomogeneous and random optical lattices. In the strong interacting limit and at very low temperatures, fermions form, together with bosons or bosonic holes, composite fermions. Composite fermions behave as a spinless interacting Fermi gas, and in the presence of local disorder they interact via random couplings and feel effective random local potential. This opens a wide variety of possibilities of realizing various kinds of ultracold quantum disordered systems. In this paper we review these possibilities, discuss the accessible quantum disordered phases, and methods for their detection. The discussed quantum phases include Fermi glasses, quantum spin glasses, {\textquotedblleft}dirty{\textquotedblright} superfluids, disordered metallic phases, and phases involving quantum percolation.}, issn = {1050-2947}, doi = {10.1103/PhysRevA.72.063616}, url = {http://link.aps.org/doi/10.1103/PhysRevA.72.063616}, author = {Ahufinger, Veronica and Sanchez-Palencia, L. and Kantian, A. and Sanpera, Anna and Lewenstein, Maciej} } @article {Ahufinger2005a, title = {Lattice Solitons in Quasicondensates}, journal = {Physical Review Letters}, volume = {94}, number = {13}, year = {2005}, month = {04/2005}, pages = {130403}, publisher = {American Physical Society}, abstract = {We analyze finite temperature effects in the generation of bright solitons in condensates in optical lattices. We show that even in the presence of strong phase fluctuations solitonic structures with a well defined phase profile can be created. We propose a novel family of variational functions which describe well the properties of these solitons and account for the nonlinear effects in the band structure. We discuss also the mobility and collisions of these localized wave packets.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.94.130403}, url = {http://link.aps.org/doi/10.1103/PhysRevLett.94.130403}, author = {Ahufinger, Veronica and Sanpera, Anna} } @article {Acin2005, title = {Multiple-copy two-state discrimination with individual measurements}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {71}, number = {3}, year = {2005}, pages = {032338}, keywords = {state discrimination}, doi = {10.1103/PhysRevA.71.032338}, url = {http://link.aps.org/abstract/PRA/v71/e032338}, author = {Ac{\'\i}n, Antonio and Bagan, Emili and Baig, Mari{\`a} and Masanes, Llu{\'\i}s and Mu{\~n}oz-Tapia, Ramon} } @article {Bramon2005, title = {Popper{\textquoteright}s test of quantum mechanics and two-photon "ghost" diffraction}, journal = {arXiv}, year = {2005}, url = {http://arxiv.org/abs/quant-ph/0507040}, author = {Bramon, Albert and Escribano, Rafel} } @article {Bagan2005, title = {Purity Estimation with Separable Measurements}, journal = {Physical Review Letters}, volume = {95}, number = {11}, year = {2005}, month = {09/2005}, pages = {110504}, publisher = {American Physical Society}, abstract = {Given a large number N of copies of a qubit state of which we wish to estimate its purity, we prove that separable-measurement protocols can be as efficient as the optimal joint-measurement one if classical communication is used. This shows that the optimal estimation of the entanglement of a two-qubit state can also be achieved asymptotically with fully separable measurements. Thus, quantum memories provide no advantage in this situation. The relationship between our global Bayesian approach and the quantum Cram{\'e}r-Rao bound is discussed.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.95.110504}, url = {http://link.aps.org/doi/10.1103/PhysRevLett.95.110504}, author = {Bagan, Emili and Ballester, M. A. and Mu{\~n}oz-Tapia, Ramon and Romero-Isart, Oriol} } @article {Navascues2005, title = {Quantum Key Distillation from Gaussian States by Gaussian Operations}, journal = {Physical Review Letters}, volume = {94}, number = {1}, year = {2005}, month = {01/2005}, pages = {010502}, publisher = {American Physical Society}, abstract = {We study the secrecy properties of Gaussian states under Gaussian operations. Although such operations are useless for quantum distillation, we prove that it is possible to distill a secret key secure against any attack from sufficiently entangled Gaussian states with nonpositive partial transposition. Moreover, all such states allow for key distillation, when Eve is assumed to perform finite-size coherent attacks before the reconciliation process.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.94.010502}, url = {http://link.aps.org/doi/10.1103/PhysRevLett.94.010502}, author = {Navascu{\'e}s, M. and Bae, J. and Cirac, J. Ignacio and Lewenstein, Maciej and Sanpera, Anna and Ac{\'\i}n, Antonio} } @inbook {SenDe2005, title = {The separability versus entanglement problem}, booktitle = {Lectures on Quantum Information}, year = {2005}, pages = {123{\textendash}146}, publisher = {Wiley}, organization = {Wiley}, isbn = {9783527405275}, doi = {10.1002/9783527618637}, url = {http://www3.wileyinterscience.com/cgi-bin/bookhome/117903246?CRETRY=1\&SRETRY=0}, author = {Sen(De), Aditi and Sen, Ujjwal and Lewenstein, Maciej and Sanpera, Anna}, editor = {Bruss, Dagmar and Leuchs, G.} } @article {Calsamiglia2005, title = {Spin Gases: Quantum Entanglement Driven by Classical Kinematics}, journal = {Physical Review Letters}, volume = {95}, number = {18}, year = {2005}, month = {10/2005}, pages = {180502}, abstract = {A spin gas is a natural extension of a classical gas. It consists of a large number of particles whose (random) motion is described classically, but, in addition, have internal (quantum mechanical) degrees of freedom that interact during collisions. For specific types of quantum interactions we determine the entanglement that occurs naturally in such systems. We analyze how the evolution of the quantum state is determined by the underlying classical kinematics of the gas. For the Boltzmann gas, we calculate the rate at which entanglement is produced and characterize the entanglement properties of the equilibrium state.}, keywords = {entanglement distribution, spin gas}, doi = {10.1103/PhysRevLett.95.180502}, url = {http://link.aps.org/abstract/PRL/v95/e180502}, author = {Calsamiglia, John and Hartmann, L. and D{\"u}r, Wolfgang and Briegel, Hans J.} } @article {Calvo2005, title = {Wigner representation and geometric transformations of optical orbital angular momentum spatial modes}, journal = {Optics Letters}, volume = {30}, number = {10}, year = {2005}, month = {05/2005}, pages = {1207}, publisher = {OSA}, abstract = {An exact Wigner representation of optical spatial modes carrying orbital angular momentum is found in closed form by exploiting the underlying SU(2) Lie-group algebra of their associated Poincar{\'e} sphere. Orthogonality relations and observables of these states are obtained within the phase space picture. Development of geometric phases on mode transformations is also elucidated.}, keywords = {Berry{\textquoteright}s phase, Mathematical methods (general), Modes, Physical optics, Propagation}, issn = {0146-9592}, doi = {10.1364/OL.30.001207}, url = {http://ol.osa.org/abstract.cfm?URI=ol-30-10-1207}, author = {Calvo, Gabriel F.} } @article {Bramon2004b, title = {Active and passive quantum erasers for neutral kaons}, journal = {Physical Review A}, volume = {69}, number = {6}, year = {2004}, issn = {1050-2947}, doi = {10.1103/PhysRevA.69.062111}, url = {http://pra.aps.org/abstract/PRA/v69/i6/e062111}, author = {Bramon, A. and Garbarino, G. and Hiesmayr, B.} } @article {Sanpera2004, title = {Atomic Fermi-Bose Mixtures in Inhomogeneous and Random Lattices: From Fermi Glass to Quantum Spin Glass and Quantum Percolation}, journal = {Physical Review Letters}, volume = {93}, number = {4}, year = {2004}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.93.040401}, url = {http://prl.aps.org/abstract/PRL/v93/i4/e040401}, author = {Sanpera, A. and Kantian, A. and Sanchez-Palencia, L. and Zakrzewski, J. and Lewenstein, M.} } @article {Kreutzmann2004, title = {Coherence Properties of Guided-Atom Interferometers}, journal = {Physical Review Letters}, volume = {92}, number = {16}, year = {2004}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.92.163201}, url = {http://prl.aps.org/abstract/PRL/v92/i16/e163201}, author = {Kreutzmann, H. and Poulsen, U. and Lewenstein, M. and Dumke, R. and Ertmer, W. and Birkl, G. and Sanpera, A.} } @article {Bagan2004, title = {Collective versus local measurements in a qubit mixed-state estimation}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {69}, number = {1}, year = {2004}, month = {01/2004}, pages = {010304}, publisher = {American Physical Society}, abstract = {We discuss the problem of estimating a qubit mixed state. We give the optimal estimation that can be inferred from any given set of measurements. For collective measurements and for a large number N of copies, we show that the error in the estimation varies as 1/N. For local measurements, we focus on the simpler case of states lying on the equatorial plane of the Bloch sphere. We show that the error using plain tomography varies as 1/N1/4, while our approach leads to an error proportional to 1/N3/4.}, issn = {1050-2947}, doi = {10.1103/PhysRevA.69.010304}, url = {http://link.aps.org/doi/10.1103/PhysRevA.69.010304}, author = {Bagan, Emili and Baig, Mari{\`a} and Mu{\~n}oz-Tapia, Ramon and Rodriguez, A.} } @article {Ahufinger2004, title = {Creation and mobility of discrete solitons in Bose-Einstein condensates}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {69}, number = {5}, year = {2004}, month = {05/2004}, pages = {053604}, publisher = {American Physical Society}, abstract = {We analyze the generation and mobility of discrete solitons in Bose-Einstein condensates confined in an optical lattice under realistic experimental conditions. We discuss first the creation of one-dimensional discrete solitons, for both attractive and repulsive interatomic interactions. We then address the issue of their mobility, focusing our attention on the conditions for the experimental observability of the Peierls-Nabarro barrier. Finally we report on the generation of self-trapped structures in two and three dimensions. Discrete solitons may open alternative routes for the manipulation and transport of Bose-Einstein condensates.}, issn = {1050-2947}, doi = {10.1103/PhysRevA.69.053604}, url = {http://link.aps.org/doi/10.1103/PhysRevA.69.053604}, author = {Ahufinger, Veronica and Sanpera, Anna and Pedri, P. and Santos, L. and Lewenstein, Maciej} } @article {Bagan2004a, title = {Entanglement-assisted alignment of reference frames using a dense covariant coding}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {69}, number = {5}, year = {2004}, month = {05/2004}, pages = {050303}, publisher = {American Physical Society}, abstract = {We present a procedure inspired by dense coding, which enables a highly efficient transmission of information of a continuous nature. The procedure requires the sender and the recipient to share a maximally entangled state. We deal with the concrete problem of aligning reference frames or trihedra by means of a quantum system. We find the optimal covariant measurement and compute the corresponding average error, which has a remarkably simple close form. The connection of this procedure with that of estimating unitary transformations on qubits is briefly discussed.}, issn = {1050-2947}, doi = {10.1103/PhysRevA.69.050303}, url = {http://link.aps.org/doi/10.1103/PhysRevA.69.050303}, author = {Bagan, Emili and Baig, Mari{\`a} and Mu{\~n}oz-Tapia, Ramon} } @article {Bourennane2004, title = {Experimental Detection of Multipartite Entanglement using Witness Operators}, journal = {Physical Review Letters}, volume = {92}, number = {8}, year = {2004}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.92.087902}, url = {http://prl.aps.org/abstract/PRL/v92/i8/e087902}, author = {Bourennane, Mohamed and Eibl, Manfred and Kurtsiefer, Christian and Gaertner, Sascha and Weinfurter, Harald and G{\"u}hne, Otfried and Hyllus, Philipp and Bru{\ss}, Dagmar and Lewenstein, Maciej and Sanpera, Anna} } @article {Baig2004, title = {Fixed boundary conditions analysis of the 3d gonihedric Ising model with k=0}, journal = {Physics Letters B}, volume = {585}, number = {1-2}, year = {2004}, pages = {180{\textendash}186}, abstract = {The gonihedric Ising model is a particular case of the class of models defined by Savvidy and Wegner intended as discrete versions of string theories on cubic lattices. In this Letter we perform a high statistics analysis of the phase transition exhibited by the 3d gonihedric Ising model with k=0 in the light of a set of recently stated scaling laws applicable to first order phase transitions with fixed boundary conditions. Even though qualitative evidence was presented in a previous paper to support the existence of a first order phase transition at k=0, only now are we capable of pinpointing the transition inverse temperature at $\beta$c=0.54757(63) and of checking the scaling of standard observables.}, keywords = {Author Keywords: Spin systems, Fixed boundary conditions, Gonihedric models, Phase transitions}, doi = {10.1016/j.physletb.2004.02.002}, url = {http://www.sciencedirect.com/science?\_ob=ArticleURL\&\_udi=B6TVN-4BSN95Y-3\&\_user=1517286\&\_coverDate=04\%2F08\%2F2004\&\_rdoc=1\&\_fmt=high\&\_orig=search\&\_sort=d\&\_docanchor=\&view=c\&\_acct=C000053449\&\_version=1\&\_urlVersion=0\&\_userid=1517286\&md5=b8fb559f9}, author = {Baig, Mari{\`a} and Clua, J. and Johnston, D. A. and Villanova, R.} } @inbook {Bramon2004c, title = {Passive Quantum Erasure for Neutral Kaons}, booktitle = {Symmetries in Gravity and Field Theory}, year = {2004}, pages = {223}, publisher = {Ediciones Universidad de Salamanca}, organization = {Ediciones Universidad de Salamanca}, address = {Salamanca}, url = {http://arxiv.org/abs/quant-ph/0404086}, author = {Bramon, Albert and Garbarino, G. and Hiesmayr, B. C.}, editor = {Aldaya, V. and Cervero, J. M.} } @inbook {Bramon2004d, title = {Popper{\textquoteright}s test of Quantum Mechanics}, booktitle = {Fundamental Physics Meeting "Alberto Galindo"}, year = {2004}, pages = {201{\textendash}207}, publisher = {Aula Documental de Investigacion}, organization = {Aula Documental de Investigacion}, address = {Madrid}, url = {http://arxiv.org/abs/quant-ph/0501134}, author = {Bramon, Albert and Escribano, Rafel}, editor = {Alvarez-Estrada, R. F. and Dobado, A. and Fernandez, L. A. and Mart\'{\i}n-Delgado, M. A. and {Munoz Sudupe}, A.} } @article {Bramon2004a, title = {Quantitative complementarity in two-path interferometry}, journal = {Physical Review A}, volume = {69}, number = {2}, year = {2004}, issn = {1050-2947}, doi = {10.1103/PhysRevA.69.022112}, url = {http://pra.aps.org/abstract/PRA/v69/i2/e022112}, author = {Bramon, A. and Garbarino, G. and Hiesmayr, B.} } @article {Bramon2004, title = {Quantum Marking and Quantum Erasure for Neutral Kaons}, journal = {Physical Review Letters}, volume = {92}, number = {2}, year = {2004}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.92.020405}, url = {http://prl.aps.org/abstract/PRL/v92/i2/e020405}, author = {Bramon, A. and Garbarino, G. and Hiesmayr, B.} } @article {Bagan2004b, title = {Quantum reverse engineering and reference-frame alignment without nonlocal correlations}, journal = {Physical Review A (Atomic, Molecular, and Optical Physics)}, volume = {70}, number = {3}, year = {2004}, month = {09/2004}, pages = {030301}, publisher = {American Physical Society}, abstract = {The estimation of unknown qubit elementary gates and the alignment of reference frames are formally the same problem. Using quantum states made out of N qubits, we show that the theoretical precision limit for both problems, which behaves as 1/N2, can be asymptotically attained with a covariant protocol that exploits the quantum correlation of internal degrees of freedom instead of the more fragile entanglement between distant parties. This cuts by half the number of qubits needed to achieve the precision of the dense covariant coding protocol.}, issn = {1050-2947}, doi = {10.1103/PhysRevA.70.030301}, url = {http://link.aps.org/doi/10.1103/PhysRevA.70.030301}, author = {Bagan, Emili and Baig, Mari{\`a} and Mu{\~n}oz-Tapia, Ramon} } @article {Hulpke2004, title = {Simplifying Schmidt number witnesses via higher-dimensional embeddings}, journal = {Quantum Information and Computation}, volume = {4}, year = {2004}, pages = {207}, author = {Hulpke, F. and Bruss, Dagmar and Lewenstein, Maciej and Sanpera, Anna} } @article {Kartashov2004, title = {Soliton Eigenvalue Control in Optical Lattices}, journal = {Physical Review Letters}, volume = {93}, number = {14}, year = {2004}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.93.143902}, url = {http://prl.aps.org/abstract/PRL/v93/i14/e143902}, author = {Kartashov, Yaroslav and Crasovan, Lucian-Cornel and Zelenina, Anna and Vysloukh, Victor and Sanpera, Anna and Lewenstein, Maciej and Torner, Lluis} } @article {Bertlmann2004, title = {Violation of a Bell inequality in particle physics experimentally verified?}, journal = {Physics Letters A}, volume = {332}, number = {5-6}, year = {2004}, pages = {355{\textendash}360}, abstract = {Relevant aspects for testing Bell inequalities with entangled meson{\textendash}antimeson systems are analyzed. In particular, we argue that the results of Go [J. Mod. Opt. 51 (2004) 991], which nicely illustrate the quantum entanglement of B-meson pairs, cannot be considered as a Bell-test refuting local realism.}, keywords = {Bell inequality, Entanglement}, doi = {10.1016/j.physleta.2004.10.006}, url = {http://www.sciencedirect.com/science?\_ob=ArticleURL\&\_udi=B6TVM-4DK6240-1\&\_user=1517286\&\_coverDate=11\%2F22\%2F2004\&\_rdoc=1\&\_fmt=high\&\_orig=search\&\_sort=d\&\_docanchor=\&view=c\&\_searchStrId=1201715030\&\_rerunOrigin=google\&\_acct=C000053449\&\_version=1}, author = {Bertlmann, R. A. and Bramon, Albert and Garbarino, G. and Hiesmayr, B. C.} } @inbook {Eckert2003, title = {Entanglement properties of composite quantum systems}, booktitle = {Quantum Information Processing}, year = {2003}, pages = {87{\textendash}95}, publisher = {Wilew-VCH}, organization = {Wilew-VCH}, address = {Berlin}, isbn = {352740371X}, author = {Eckert, Kai and Guhne, O. and Hulpke, Florian and Hyllus, Philipp and Korbicz, J. and Mompart, Jordi and Bruss, Dagmar and Lewenstein, Maciej and Sanpera, Anna}, editor = {Leuchs, G. and Beth, T.} } @article {Guhne2003, title = {Experimental detection of entanglement via witness operators and local measurements}, journal = {Journal of Modern Optics}, volume = {50}, number = {6-7}, year = {2003}, pages = {1079{\textendash}1102}, doi = {10.1080/09500340308234554}, url = {http://www.informaworld.com/smpp/36433790-99697256/content\~{}db=all\~{}content=a713826204}, author = {G{\"u}hne, Otfried and Hyllus, Philipp and Bruss, Dagmar and Ekert, Artur K. and Lewenstein, Maciej and Macchiavello, Chiara and Sanpera, Anna} } @article {Bagan2003, title = {Minimal measurements of the gate fidelity of a qudit map}, journal = {Physical Review A}, volume = {67}, number = {1}, year = {2003}, issn = {1050-2947}, doi = {10.1103/PhysRevA.67.014303}, url = {http://pra.aps.org/abstract/PRA/v67/i1/e014303}, author = {E. Bagan and Baig, M. and Mu{\~n}oz-Tapia, R.} } @conference {Bagan2003a, title = {Optimal reconstruction of a pure qubit state with local measurements}, booktitle = {Proceedings of the 8th ICSSUR}, year = {2003}, publisher = {Rinton Press (2003)}, organization = {Rinton Press (2003)}, author = {Bagan, Emili and Baig, Mari{\`a} and Monras, Alex and Mu{\~n}oz-Tapia, Ramon} } @article {Bramon2003a, title = {Quantitative duality and neutral kaon interferometry}, journal = {The European Physical Journal C - Particles and Fields}, volume = {32}, number = {3}, year = {2003}, month = {01/2003}, pages = {377{\textendash}380}, abstract = {A quantitative formulation of Bohr\&\#8217;s complementarity principle and interferometric duality is discussed and applied to the neutral kaon system. Recent measurements by the CPLEAR Collaboration can be easily interpreted in terms of neutral kaon interferometry, illustrating and confirming those basic principles of quantum mechanics. The subject can be further investigated at the operational \$\backslash phi\$ -factory Daphne.}, issn = {1434-6044}, doi = {10.1140/epjc/s2003-01444-5}, url = {http://www.springerlink.com/content/4l12acw6kn9xkfbt}, author = {Bramon, A. and Garbarino, Gianni and Hiesmayr, B. C.} } @conference {Bramon2003, title = {Quantitative duality and quantum erasure for neutral kaons}, booktitle = {eConf C0309101:THWP005}, year = {2003}, author = {Bramon, Albert and Garbarino, Gianni and Hiesmayr, Beatrix C.} } @article {Guhne2002, title = {Detection of entanglement with few local measurements}, journal = {Physical Review A}, volume = {66}, number = {6}, year = {2002}, issn = {1050-2947}, doi = {10.1103/PhysRevA.66.062305}, url = {http://pra.aps.org/abstract/PRA/v66/i6/e062305}, author = {G{\"u}hne, O. and Hyllus, P. and Bru{\ss}, D. and Ekert, A. and Lewenstein, M. and Macchiavello, C. and Sanpera, A.} } @article {Bramon2002, title = {Novel Bell{\textquoteright}s Inequalities for Entangled K0K{\textasciimacron}0 Pairs}, journal = {Physical Review Letters}, volume = {88}, number = {4}, year = {2002}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.88.040403}, url = {http://prl.aps.org/abstract/PRL/v88/i4/e040403}, author = {Bramon, Albert and Garbarino, Gianni} } @article {Bagan2002, title = {Optimal Scheme for Estimating a Pure Qubit State via Local Measurements}, journal = {Physical Review Letters}, volume = {89}, number = {27}, year = {2002}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.89.277904}, url = {http://prl.aps.org/abstract/PRL/v89/i27/e277904}, author = {E. Bagan and Baig, M. and Mu{\~n}oz-Tapia, R.} } @article {Baig2002, title = {Scaling laws for the two-dimensional eight-state Potts model with fixed boundary conditions}, journal = {Physical Review B}, volume = {65}, number = {9}, year = {2002}, issn = {0163-1829}, doi = {10.1103/PhysRevB.65.094428}, url = {http://prb.aps.org/abstract/PRB/v65/i9/e094428}, author = {Baig, M. and Villanova, R.} } @article {Bramon2002a, title = {Test of Local Realism with Entangled Kaon Pairs and without Inequalities}, journal = {Physical Review Letters}, volume = {89}, number = {16}, year = {2002}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.89.160401}, url = {http://prl.aps.org/abstract/PRL/v89/i16/e160401}, author = {Bramon, Albert and Garbarino, Gianni} } @article {Bagan2001b, title = {Aligning Reference Frames with Quantum States}, journal = {arXiv}, year = {2001}, url = {http://arxiv.org/abs/quant-ph/0106155}, author = {Bagan, Emili and Baig, Mari{\`a} and Mu{\~n}oz-Tapia, Ramon} } @article {Bagan2001a, title = {Aligning Reference Frames with Quantum States}, journal = {Physical Review Letters}, volume = {87}, number = {25}, year = {2001}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.87.257903}, url = {http://prl.aps.org/abstract/PRL/v87/i25/e257903}, author = {E. Bagan and Baig, M. and Mu{\~n}oz-Tapia, R.} } @article {Acin2001, title = {Classification of Mixed Three-Qubit States}, journal = {Physical Review Letters}, volume = {87}, number = {4}, year = {2001}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.87.040401}, url = {http://prl.aps.org/abstract/PRL/v87/i4/e040401}, author = {Ac{\'\i}n, A. and Bru{\ss}, D. and Lewenstein, M. and Sanpera, A.} } @article {Bagan2001, title = {Communication of spin directions with product states and finite measurements}, journal = {Physical Review A}, volume = {64}, number = {2}, year = {2001}, issn = {1050-2947}, doi = {10.1103/PhysRevA.64.022305}, url = {http://pra.aps.org/abstract/PRA/v64/i2/e022305}, author = {E. Bagan and Baig, M. and Mu{\~n}oz-Tapia, R.} } @article {Salieres2001, title = {Feynman{\textquoteright}s path-integral approach for intense-laser-atom interactions}, journal = {Science (New York, N.Y.)}, volume = {292}, number = {5518}, year = {2001}, pages = {902{\textendash}5}, abstract = {Atoms interacting with intense laser fields can emit electrons and photons of very high energies. An intuitive and quantitative explanation of these highly nonlinear processes can be found in terms of a generalization of classical Newtonian particle trajectories, the so-called quantum orbits. Very few quantum orbits are necessary to reproduce the experimental results. These orbits are clearly identified, thus opening the way for an efficient control as well as previously unknown applications of these processes.}, issn = {0036-8075}, doi = {10.1126/science.108836}, url = {http://www.sciencemag.org/cgi/content/abstract/292/5518/902}, author = {Salieres, P. and Carre, B. and Le Deroff, L. and Grasbon, F. and Paulus, G. G. and Walther, H. and Kopold, R. and Becker, W. and Milosevic, D. B. and Sanpera, A. and Lewenstein, M.} } @article {Bagan2001c, title = {Optimal encoding and decoding of a spin direction}, journal = {Physical Review A}, volume = {63}, number = {5}, year = {2001}, issn = {1050-2947}, doi = {10.1103/PhysRevA.63.052309}, url = {http://pra.aps.org/abstract/PRA/v63/i5/e052309}, author = {E. Bagan and Baig, M. and Brey, A. and Mu{\~n}oz-Tapia, R. and Tarrach, R.} } @article {Sanpera2001, title = {Schmidt-number witnesses and bound entanglement}, journal = {Physical Review A}, volume = {63}, number = {5}, year = {2001}, issn = {1050-2947}, doi = {10.1103/PhysRevA.63.050301}, url = {http://pra.aps.org/abstract/PRA/v63/i5/e050301}, author = {Sanpera, Anna and Bru{\ss}, Dagmar and Lewenstein, Maciej} } @article {798, title = {Optimal Strategies for Sending Information through A Quantum Channel}, journal = {Physical Review Letters}, volume = {85}, year = {2000}, month = {Jan-12-2000}, pages = {5230 - 5233}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.85.5230}, url = {http://link.aps.org/doi/10.1103/PhysRevLett.85.5230http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevLett.85.5230/fulltexthttp://link.aps.org/article/10.1103/PhysRevLett.85.5230}, author = {Bagan, E. and Baig, M. and Brey, A. and Mu{\~n}oz-Tapia, R. and Tarrach, R.} } @article {Lewenstein2000, title = {Separability and distillability in composite quantum systems - a primer}, journal = {Journal of Modern Optics}, volume = {47}, number = {14-15}, year = {2000}, pages = {2481{\textendash}2499}, doi = {10.1080/09500340008232176}, url = {http://www.informaworld.com/smpp/6084610-44811133/content\~{}db=all\~{}content=a755833577}, author = {Lewenstein, Maciej and Bru{\ss}, Dagmar and Cirac, J. Ignacio and Kraus, Barbara and Ku{\'s}, M. and Samsonowicz, J. and Sanpera, Anna and Tarrach, R.} } @conference { ISI:000448139300404, title = {{Fully Quantum Arbitrarily Varying Channels: Random Coding Capacity and Capacity Dichotomy}}, booktitle = {{2018 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY (ISIT)}}, series = {{IEEE International Symposium on Information Theory}}, note = {{IEEE International Symposium on Information Theory (ISIT), Vail, CO, JUN 17-22, 2018}}, pages = {{2012-2016}}, publisher = {{IEEE; IEEE Informat Theory Soc; NSF; Huawei; Qualcomm}}, organization = {{IEEE; IEEE Informat Theory Soc; NSF; Huawei; Qualcomm}}, abstract = {{We consider a model of communication via a fully quantum jammer channel with quantum jammer, quantum sender and quantum receiver, which we dub quantum arbitrarily varying channel (QAVC). Restricting to finite dimensional user and jammer systems, we show, using permutation symmetry and a de Finetti reduction, how the random coding capacity (classical and quantum) of the QAVC is reduced to the capacity of a naturally associated compound channel, which is obtained by restricting the jammer to i.i.d. input states. Furthermore, we demonstrate that the shared randomness required is at most logarithmic in the block length, via a quantum version of the {\textquoteleft}{\textquoteleft}elimination of of correlation{{\textquoteright}{\textquoteright}} using a random matrix tail bound. This implies a dichotomy theorem: either the classical capacity of the QAVC is zero, and then also the quantum capacity is zero, or each capacity equals its random coding variant.}}, isbn = {{978-1-5386-4781-3}}, author = {Boche, Holger and Deppe, Christian and Noetzel, Janis and Winter, Andreas} } @article { ISI:000418336400003, title = {{Generalized laws of thermodynamics in the presence of correlations}}, journal = {{NATURE COMMUNICATIONS}}, volume = {{8}}, month = {{DEC 19}}, abstract = {{The laws of thermodynamics, despite their wide range of applicability, are known to break down when systems are correlated with their environments. Here we generalize thermodynamics to physical scenarios which allow presence of correlations, including those where strong correlations are present. We exploit the connection between information and physics, and introduce a consistent redefinition of heat dissipation by systematically accounting for the information flow from system to bath in terms of the conditional entropy. As a consequence, the formula for the Helmholtz free energy is accordingly modified. Such a remedy not only fixes the apparent violations of Landauer{\textquoteright}s erasure principle and the second law due to anomalous heat flows, but also leads to a generally valid reformulation of the laws of thermodynamics. In this information-theoretic approach, correlations between system and environment store work potential. Thus, in this view, the apparent anomalous heat flows are the refrigeration processes driven by such potentials.}}, issn = {{2041-1723}}, doi = {{10.1038/s41467-017-02370-x}}, author = {Bera, Manabendra N. and Riera, Arnau and Lewenstein, Maciej and Winter, Andreas} } @article {919, title = {{Quantum reference frames and their applications to thermodynamics}}, journal = {{PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES}}, volume = {{376}}, number = {{2123}}, month = {{JUL 13}}, abstract = {{We construct a quantum reference frame, which can be used to approximately implement arbitrary unitary transformations on a system in the presence of any number of extensive conserved quantities, by absorbing any back action provided by the conservation laws. Thus, the reference frame at the same time acts as a battery for the conserved quantities. Our construction features a physically intuitive, clear and implementation-friendly realization. Indeed, the reference system is composed of the same types of subsystems as the original system and is finite for any desired accuracy. In addition, the interaction with the reference frame can be broken down into two-body terms coupling the system to one of the reference frame subsystems at a time. We apply this construction to quantum thermodynamic set-ups with multiple, possibly non-commuting conserved quantities, which allows for the definition of explicit batteries in such cases. This article is part of a discussion meeting issue {\textquoteleft}Foundations of quantum mechanics and their impact on contemporary society{\textquoteright}.}

}, issn = {{1364-503X}}, doi = {{10.1098/rsta.2018.0111}}, author = {Popescu, Sandu and Belen Sainz, Ana and Short, Anthony J. and Winter, Andreas} } @conference { ISI:000448139300537, title = {{Secure and Robust Identification via Classical-Quantum Channels}}, booktitle = {{2018 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY (ISIT)}}, series = {{IEEE International Symposium on Information Theory}}, note = {{IEEE International Symposium on Information Theory (ISIT), Vail, CO, JUN 17-22, 2018}}, pages = {{2674-2678}}, publisher = {{IEEE; IEEE Informat Theory Soc; NSF; Huawei; Qualcomm}}, organization = {{IEEE; IEEE Informat Theory Soc; NSF; Huawei; Qualcomm}}, abstract = {{We study the identification capacity of classical-quantum channels ({{\textquoteright}{\textquoteright}}cq-channels{{\textquoteright}{\textquoteright}}), under channel uncertainty and privacy constraints. To be precise, we consider first compound memoryless cq-channels and determine their identification capacity; then we add an eavesdropper, considering compound memoryless wiretap cqq-channels, and determine their secret identification capacity. In the first case (without privacy), we find the identification capacity always equal to the transmission capacity. In the second case, we find a dichotomy: either the secrecy capacity (also known as private capacity) of the channel is zero, and then also the secrecy identification capacity is zero, or the secrecy capacity is positive and then the secrecy identification capacity equals the transmission capacity of the main channel without the wiretapper. We perform the same analysis for the case of arbitrarily varying wiretap cqq-channels (cqq-AVWC), with analogous findings, and make several observations regarding the continuity and super-additivity of the identification capacity in the latter case.}}, isbn = {{978-1-5386-4781-3}}, author = {Boche, Holger and Deppe, Christian and Winter, Andreas} }