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.

VL - 118 ER - TY - JOUR T1 - Interferometric visibility and coherence JF - PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES Y1 - 2017 A1 - Biswas, Tanmoy A1 - Garcia Diaz, Maria A1 - Winter, Andreas AB - 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. VL - 473 ER - TY - JOUR T1 - Macroscopic superpositions require tremendous measurement devices JF - Quantum Y1 - 2017 A1 - Skotiniotis, Michalis A1 - Dür, Wolfgang A1 - Sekatski, Pavel AB - Michalis Skotiniotis, Wolfgang Dür, 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,… VL - 1 UR - https://quantum-journal.org/papers/q-2017-11-21-34/ ER - TY - JOUR T1 - Magnetic phases of spin-1 lattice gases with random interactions JF - PHYSICAL REVIEW B Y1 - 2017 A1 - McAlpine, Kenneth D. A1 - Paganelli, Simone A1 - Ciuchi, Sergio A1 - Sanpera, Anna A1 - De Chiara, Gabriele AB - 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. VL - 95 ER - TY - JOUR T1 - Quantum metrology with full and fast quantum control JF - Quantum Y1 - 2017 A1 - Sekatski, Pavel A1 - Skotiniotis, Michalis A1 - Kołodyński, Janek A1 - Dür, Wolfgang AB - Pavel Sekatski, Michalis Skotiniotis, Janek Kołodyński, and Wolfgang Dür, 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… VL - 1 UR - https://quantum-journal.org/papers/q-2017-09-06-27/ ER - TY - JOUR T1 - Resource theory of coherence: Beyon} states JF - PHYSICAL REVIEW A Y1 - 2017 A1 - Ben Dana, Khaled A1 - Garcia Diaz, Maria A1 - Mejatty, Mohamed A1 - Winter, Andreas AB -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 (”incoherent”) 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 “strictly incoherent” 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.

VL - 95 ER - TY - JOUR T1 - No-Signalling-Assisted Zero-Error Capacity of Quantum Channels and an Information Theoretic Interpretation of the Lovász Number JF - IEEE Transactions on Information Theory Y1 - 2016 A1 - Duan, Runyao A1 - Winter, Andreas VL - 62 IS - 2 JO - IEEE Trans. Inform. Theory ER - TY - JOUR T1 - Should Entanglement Measures be Monogamous or Faithful? JF - Physical Review Letters Y1 - 2016 A1 - Lancien, Cécilia A1 - Di Martino, Sara A1 - Huber, Marcus A1 - Piani, Marco A1 - Adesso, Gerardo A1 - Winter, Andreas VL - 117 IS - 6 JO - Phys. Rev. Lett. ER - TY - JOUR T1 - On {Zero}-{Error} {Communication} via {Quantum} {Channels} in the {Presence} of {Noiseless} {Feedback} JF - IEEE Transactions on Information Theory Y1 - 2016 A1 - Duan, R. A1 - Severini, S. A1 - Winter, A. KW - bipartite equivocation graph KW - Bipartite graph KW - Capacity planning KW - Choi-Kraus operators KW - coding theorem KW - commutative bipartite graph KW - Electronic mail KW - encoding KW - entanglement-assisted capacity KW - feedback KW - feedback-assisted capacity KW - feedback-assisted zero-error capacity KW - information theory KW - noiseless feedback channel KW - quantum channels KW - quantum communication KW - quantum entanglement KW - Quantum information KW - Receivers KW - Shannon's zero-error communication KW - telecommunication channels KW - unlimited quantum capacity KW - zero-error capacity AB - 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'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. VL - 62 ER - TY - JOUR T1 - Case study of the uniaxial anisotropic spin-1 bilinear-biquadratic Heisenberg model on a triangular lattice JF - Physical Review B Y1 - 2014 A1 - Moreno-Cardoner, M. A1 - Perrin, H. A1 - Paganelli, S. A1 - De Chiara, G. A1 - Sanpera, A. AB - 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. VL - 90 IS - 14 JO - Phys. Rev. B ER - TY - Generic T1 - Constant compositions in the sphere packing bound for classical-quantum channels T2 - 2014 IEEE International Symposium on Information Theory (ISIT) Y1 - 2014 A1 - Dalai, Marco A1 - Winter, Andreas JF - 2014 IEEE International Symposium on Information Theory (ISIT) PB - IEEE CY - Honolulu, HI, USA ER - TY - JOUR T1 - Entanglement properties of spin models in triangular lattices JF - Journal of Statistical Mechanics: Theory and Experiment Y1 - 2014 A1 - Moreno-Cardoner, M. A1 - Paganelli, S. A1 - De Chiara, G. A1 - Sanpera, A. AB - 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. VL - 2014 IS - 10 JO - J. Stat. Mech. ER - TY - JOUR T1 - Long-range multipartite entanglement close to a first-order quantum phase transition JF - Physical Review A Y1 - 2014 A1 - Stasińska, J. A1 - Rogers, B. A1 - M. Paternostro A1 - De Chiara, G. A1 - Sanpera, A. AB - 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. VL - 89 IS - 3 JO - Phys. Rev. A ER - TY - JOUR T1 - The Quantum Reverse Shannon Theorem and Resource Tradeoffs for Simulating Quantum Channels JF - IEEE Transactions on Information Theory Y1 - 2014 A1 - Bennett, Charles H. A1 - Devetak, Igor A1 - Harrow, Aram W. A1 - Shor, Peter W. A1 - Winter, Andreas VL - 60 IS - 5 JO - IEEE Trans. Inform. Theory ER - TY - JOUR T1 - Decomposition of any quantum measurement into extremals JF - Journal of Physics A: Mathematical and Theoretical Y1 - 2013 A1 - Sentís, G A1 - Gendra, B. A1 - Bartlett, S D A1 - Doherty, A C VL - 46 IS - 37 JO - J. Phys. A: Math. Theor. ER - TY - CHAP T1 - Identification via Quantum Channels T2 - Information Theory, Combinatorics, and Search Theory: In Memory of Rudolf Ahlswede Y1 - 2013 A1 - Winter, Andreas ED - Aydinian, Harout ED - Cicalese, Ferdinando ED - Deppe, Christian JF - Information Theory, Combinatorics, and Search Theory: In Memory of Rudolf Ahlswede T3 - Lecture Notes in Computer Science PB - Springer Berlin Heidelberg CY - Berlin, Heidelberg VL - LNCS 7777 SN - 978-3-642-36899-8 ER - TY - JOUR T1 - Quantum Rate-Distortion Coding With Auxiliary Resources JF - IEEE Transactions on Information Theory Y1 - 2013 A1 - Wilde, Mark M. A1 - Datta, Nilanjana A1 - Hsieh, Min-Hsiu A1 - Winter, Andreas VL - 59 IS - 10 JO - IEEE Trans. Inform. Theory ER - TY - JOUR T1 - Quantum-to-classical rate distortion coding JF - Journal of Mathematical Physics Y1 - 2013 A1 - Datta, Nilanjana A1 - Hsieh, Min-Hsiu A1 - Wilde, Mark M. A1 - Winter, Andreas VL - 54 IS - 4 JO - J. Math. Phys. ER - TY - JOUR T1 - Scaling of the entanglement spectrum near quantum phase transitions JF - Physical Review B Y1 - 2013 A1 - Lepori, L. A1 - De Chiara, G. A1 - Sanpera, A. VL - 87 IS - 23 JO - Phys. Rev. B ER - TY - JOUR T1 - Zero-Error Communication via Quantum Channels, Noncommutative Graphs, and a Quantum Lovász Number JF - IEEE Transactions on Information Theory Y1 - 2013 A1 - Duan, Runyao A1 - Severini, Simone A1 - Winter, Andreas VL - 59 IS - 2 JO - IEEE Trans. Inform. Theory ER - TY - JOUR T1 - Entanglement Spectrum, Critical Exponents, and Order Parameters in Quantum Spin Chains JF - Physical Review Letters Y1 - 2012 A1 - De Chiara, G. A1 - Lepori, L. A1 - Lewenstein, M. A1 - Sanpera, A. AB - 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. VL - 109 IS - 23 JO - Phys. Rev. Lett. ER - TY - JOUR T1 - Bilinear-biquadratic spin-1 chain undergoing quadratic Zeeman effect JF - Physical Review B Y1 - 2011 A1 - De Chiara, G. A1 - Lewenstein, M. A1 - Sanpera, A. AB - 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. VL - 84 UR - http://prb.aps.org/abstract/PRB/v84/i5/e054451 IS - 5 JO - Phys. Rev. B ER - TY - JOUR T1 - Entanglement detection in hybrid optomechanical systems JF - Phys. Rev. A Y1 - 2011 A1 - De Chiara, Gabriele A1 - Paternostro, Mauro A1 - Palma, G. Massimo AB - 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. VL - 83 UR - http://link.aps.org/doi/10.1103/PhysRevA.83.052324 ER - TY - JOUR T1 - Entangling two distant oscillators with a quantum reservoir JF - EPL (Europhysics Letters) Y1 - 2011 A1 - Wolf, A A1 - De Chiara, G. A1 - Kajari, E A1 - Lutz, E A1 - G. Morigi AB - 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'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. VL - 95 UR - http://epljournal.edpsciences.org/index.php?option=com_article&access=standard&Itemid=129&url=/articles/epl/abs/2011/18/epl13816/epl13816.html IS - 6 JO - EPL ER - TY - JOUR T1 - Probing magnetic order in ultracold lattice gases JF - Phys. Rev. A Y1 - 2011 A1 - De Chiara, Gabriele A1 - O. Romero-Isart A1 - Sanpera, A. AB - 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. VL - 83 UR - http://pra.aps.org/abstract/PRA/v83/i2/e021604 ER - TY - JOUR T1 - Quantifying, characterizing, and controlling information flow in ultracold atomic gases JF - Physical Review A Y1 - 2011 A1 - Haikka, P. A1 - McEndoo, S. A1 - De Chiara, G. A1 - G. M. Palma A1 - Maniscalco, S. AB - 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). VL - 84 UR - http://pra.aps.org/abstract/PRA/v84/i3/e031602 IS - 3 JO - Phys. Rev. A ER - TY - JOUR T1 - Cold-atom induced control of an opto-mechanical device JF - Phys. Rev. Lett. Y1 - 2010 A1 - M. Paternostro A1 - De Chiara, Gabriele A1 - G. M. Palma AB - 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. VL - 104 UR - http://link.aps.org/doi/10.1103/PhysRevLett.104.243602 ER - TY - JOUR T1 - The quantum ground state of self-organized atomic crystals in optical resonators JF - Phys. Rev. A Y1 - 2010 A1 - S. Fernández-Vidal A1 - De Chiara, Gabriele A1 - J. Larson A1 - G. Morigi AB - 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. VL - 81 UR - http://link.aps.org/doi/10.1103/PhysRevA.81.043407 ER - TY - JOUR T1 - Spontaneous nucleation of structural defects in inhomogeneous ion chains JF - New. J. Phys. Y1 - 2010 A1 - De Chiara, Gabriele A1 - del Campo, Adolfo A1 - G. Morigi A1 - M. B. Plenio A1 - A. Retzker AB - 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. VL - 12 UR - http://iopscience.iop.org/1367-2630/12/11/115003?fromSearchPage=true ER - TY - JOUR T1 - Structural defects in ion crystals by quenching the external potential: the inhomogeneous Kibble-Zurek mechanism JF - Phys. Rev. Lett. Y1 - 2010 A1 - del Campo, Adolfo A1 - De Chiara, Gabriele A1 - G. Morigi A1 - M. B. Plenio A1 - A. Retzker VL - 105 UR - http://link.aps.org/doi/10.1103/PhysRevLett.105.075701 ER - TY - JOUR T1 - Frustration, Area Law, and Interference in Quantum Spin Models JF - Physical Review Letters Y1 - 2008 A1 - Sen(De), Aditi A1 - Sen, Ujjwal A1 - Dziarmaga, Jacek A1 - Sanpera, Anna A1 - Lewenstein, Maciej VL - 101 UR - http://link.aps.org/abstract/PRL/v101/e187202 ER - TY - JOUR T1 - Quantum-limited metrology with product states JF - Physical Review A (Atomic, Molecular, and Optical Physics) Y1 - 2008 A1 - Boixo, Sergio A1 - Datta, Animesh A1 - Flammia, Steven T. A1 - Shaji, Anil A1 - Bagan, Emili A1 - Caves, Carlton M. KW - angular momentum theory KW - Bose-Einstein condensation KW - bound states KW - protocols KW - quantum entanglement VL - 77 UR - http://link.aps.org/abstract/PRA/v77/e012317 ER - TY - JOUR T1 - How to hide a secret direction JF - New Journal of Physics Y1 - 2007 A1 - Bagan, Emili A1 - Calsamiglia, John A1 - Demkowicz-Dobrzanski, R. A1 - Muñoz-Tapia, Ramon AB - 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. VL - 9 UR - http://iopscience.iop.org/1367-2630/9/8/244/pdf/1367-2630\_9\_8\_244.pdf ER - TY - JOUR T1 - Ultracold atomic gases in optical lattices: mimicking condensed matter physics and beyond JF - Advances in Physics Y1 - 2007 A1 - Lewenstein, Maciej A1 - Sanpera, Anna A1 - Ahufinger, Veronica A1 - Damski, B. A1 - Sen(De), Aditi A1 - Sen, Ujjwal KW - optical lattices VL - 56 UR - http://www.informaworld.com/smpp/ftinterface\~content=a778175433\~fulltext=713240930 ER - TY - JOUR T1 - Weighted graph states and applications to spin chains, lattices and gases JF - Journal of Physics B: Atomic, Molecular and Optical Physics Y1 - 2007 A1 - Hartmann, L. A1 - Calsamiglia, John A1 - Dür, Wolfgang A1 - Briegel, Hans J. VL - 40 UR - http://www.iop.org/EJ/abstract/0953-4075/40/9/S01 ER - TY - JOUR T1 - Spin Gases: Quantum Entanglement Driven by Classical Kinematics JF - Physical Review Letters Y1 - 2005 A1 - Calsamiglia, John A1 - Hartmann, L. A1 - Dür, Wolfgang A1 - Briegel, Hans J. KW - entanglement distribution KW - spin gas AB - 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. VL - 95 UR - http://link.aps.org/abstract/PRL/v95/e180502 ER - TY - JOUR T1 - Coherence Properties of Guided-Atom Interferometers JF - Physical Review Letters Y1 - 2004 A1 - Kreutzmann, H. A1 - Poulsen, U. A1 - Lewenstein, M. A1 - Dumke, R. A1 - Ertmer, W. A1 - Birkl, G. A1 - Sanpera, A. VL - 92 UR - http://prl.aps.org/abstract/PRL/v92/i16/e163201 ER - TY - CHAP T1 - Popper's test of Quantum Mechanics T2 - Fundamental Physics Meeting "Alberto Galindo" Y1 - 2004 A1 - Bramon, Albert A1 - Escribano, Rafel ED - Alvarez-Estrada, R. F. ED - Dobado, A. ED - Fernandez, L. A. ED - Mart\'ın-Delgado, M. A. ED - {Munoz Sudupe}, A. JF - Fundamental Physics Meeting "Alberto Galindo" PB - Aula Documental de Investigacion CY - Madrid UR - http://arxiv.org/abs/quant-ph/0501134 ER - TY - CONF T1 - {Fully Quantum Arbitrarily Varying Channels: Random Coding Capacity and Capacity Dichotomy} T2 - {2018 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY (ISIT)} Y1 - 0 A1 - Boche, Holger A1 - Deppe, Christian A1 - Noetzel, Janis A1 - Winter, Andreas AB - {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 ``elimination of of correlation{''} 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.} JF - {2018 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY (ISIT)} T3 - {IEEE International Symposium on Information Theory} PB - {IEEE; IEEE Informat Theory Soc; NSF; Huawei; Qualcomm} SN - {978-1-5386-4781-3} N1 - {IEEE International Symposium on Information Theory (ISIT), Vail, CO, JUN 17-22, 2018} ER - TY - CONF T1 - {Secure and Robust Identification via Classical-Quantum Channels} T2 - {2018 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY (ISIT)} Y1 - 0 A1 - Boche, Holger A1 - Deppe, Christian A1 - Winter, Andreas AB - {We study the identification capacity of classical-quantum channels ({''}cq-channels{''}), 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.} JF - {2018 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY (ISIT)} T3 - {IEEE International Symposium on Information Theory} PB - {IEEE; IEEE Informat Theory Soc; NSF; Huawei; Qualcomm} SN - {978-1-5386-4781-3} N1 - {IEEE International Symposium on Information Theory (ISIT), Vail, CO, JUN 17-22, 2018} ER -