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.

%B PHYSICAL REVIEW E %V 96 %R 10.1103/PhysRevE.96.030103 %0 Journal Article %J PHYSICAL REVIEW A %D 2017 %T Logarithmic coherence: Operational interpretation of l(1)-norm coherence %A Rana, Swapan %A Parashar, Preeti %A Winter, Andreas %A Lewenstein, Maciej %XWe 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.

%B PHYSICAL REVIEW A %V 96 %R 10.1103/PhysRevA.96.052336 %0 Journal Article %J PHYSICAL REVIEW B %D 2017 %T Magnetic phases of spin-1 lattice gases with random interactions %A McAlpine, Kenneth D. %A Paganelli, Simone %A Ciuchi, Sergio %A Sanpera, Anna %A De Chiara, Gabriele %X 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. %B PHYSICAL REVIEW B %V 95 %8 jun %R 10.1103/PhysRevB.95.235128 %0 Journal Article %J PHYSICAL REVIEW LETTERS %D 2017 %T No-Go Theorem for the Characterization of Work Fluctuations in Coherent Quantum Systems %A Perarnau-Llobet, Marti %A Baumer, Elisa %A Hovhannisyan, Karen V. %A Huber, Marcus %A Acín, Antonio %XAn 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.

%B PHYSICAL REVIEW LETTERS %V 118 %R 10.1103/PhysRevLett.118.070601 %0 Journal Article %J Physical Review A %D 2017 %T Vortex stability in Bose-Einstein condensates in the presence of disorder %A Pons, Marisa %A Sanpera, Anna %B Physical Review A %V 95 %8 Jan-03-2017 %U 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 %! Phys. Rev. A %R 10.1103/PhysRevA.95.033626 %0 Journal Article %J Physical Review B %D 2016 %T Autonomous {Quantum} {Refrigerator} in a {Circuit}-{QED} {Architecture} {Based} on a {Josephson} {Junction} %A Hofer, Patrick P. %A Perarnau-Llobet, Marti %A Brask, Jonatan Bohr %A Silva, Ralph %A Huber, Marcus %A Brunner, Nicolas %K Condensed Matter - Mesoscale and Nanoscale Physics %K Quantum Physics %X 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. %B Physical Review B %V 94 %U http://arxiv.org/abs/1607.05218 %R 10.1103/PhysRevB.94.235420 %0 Journal Article %J Journal of Functional Analysis %D 2016 %T Estimating quantum chromatic numbers %A Paulsen, Vern I. %A Severini, Simone %A Stahlke, Daniel %A Todorov, Ivan G. %A Winter, Andreas %B Journal of Functional Analysis %V 270 %P 2188-2222 %8 03/2016 %N 6 %! Journal of Functional Analysis %R 10.1016/j.jfa.2016.01.010 %0 Journal Article %J Quantum Science and Technology %D 2016 %T Realising a quantum absorption refrigerator with an atom-cavity system %A Mitchison, Mark T. %A Huber, Marcus %A Prior, Javier %A Woods, Mischa P. %A Plenio, Martin B. %X 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. %B Quantum Science and Technology %V 1 %P 015001 %U http://stacks.iop.org/2058-9565/1/i=1/a=015001 %R 10.1088/2058-9565/1/1/015001 %0 Journal Article %J Physical Review Letters %D 2016 %T Should Entanglement Measures be Monogamous or Faithful? %A Lancien, Cécilia %A Di Martino, Sara %A Huber, Marcus %A Piani, Marco %A Adesso, Gerardo %A Winter, Andreas %B Physical Review Letters %V 117 %8 8/2016 %N 6 %! Phys. Rev. Lett. %R 10.1103/PhysRevLett.117.060501 %0 Journal Article %J New Journal of Physics %D 2015 %T Coherence-assisted single-shot cooling by quantum absorption refrigerators %A Mitchison, Mark T %A Woods, Mischa P %A Prior, Javier %A Huber, Marcus %B New Journal of Physics %V 17 %P 115013 %G eng %U http://stacks.iop.org/1367-2630/17/i=11/a=115013?key=crossref.3c2d7f1bc5de4bbea1cba38fd2236293 %R 10.1088/1367-2630/17/11/115013 %0 Journal Article %J Optica %D 2015 %T Experimental access to higher-dimensional entangled quantum systems using integrated optics %A Christoph Schaeff %A Robert Polster %A Huber, Marcus %A Ramelow, Sven %A Anton Zeilinger %K Integrated optics %K quantum optics %X 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. %B Optica %I OSA %V 2 %P 523–529 %8 Jun %G eng %U http://www.osapublishing.org/optica/abstract.cfm?URI=optica-2-6-523 %R 10.1364/OPTICA.2.000523 %0 Journal Article %J Physical Review X %D 2015 %T Extractable Work from Correlations %A Martí Perarnau-Llobet %A Karen V. Hovhannisyan %A Huber, Marcus %A Paul Skrzypczyk %A Nicolas Brunner %A Acín, Antonio %B Physical Review X %V 5 %8 oct %G eng %U http://link.aps.org/doi/10.1103/PhysRevX.5.041011 %R 10.1103/PhysRevX.5.041011 %0 Journal Article %J Physical Review E %D 2015 %T Most energetic passive states %A Martí Perarnau-Llobet %A Karen V. Hovhannisyan %A Huber, Marcus %A Paul Skrzypczyk %A Tura, Jordi %A Acín, Antonio %B Physical Review E %V 92 %G eng %U http://link.aps.org/doi/10.1103/PhysRevE.92.042147 %R 10.1103/PhysRevE.92.042147 %0 Journal Article %J New Journal of Physics %D 2015 %T Thermodynamic cost of creating correlations %A Huber, Marcus %A Martí Perarnau-Llobet %A Karen V. Hovhannisyan %A Paul Skrzypczyk %A Klöckl, Claude %A Nicolas Brunner %A Acín, Antonio %B New Journal of Physics %V 17 %P 065008 %G eng %U http://stacks.iop.org/1367-2630/17/i=6/a=065008?key=crossref.b9c20f4bb628b09efcb912347c01851e %R 10.1088/1367-2630/17/6/065008 %0 Journal Article %J Physical Review E %D 2015 %T Thermodynamics of creating correlations: {Limitations} and optimal protocols %A Bruschi, David Edward %A Martí Perarnau-Llobet %A Friis, Nicolai %A Karen V. Hovhannisyan %A Huber, Marcus %B Physical Review E %V 91 %8 mar %G eng %U http://link.aps.org/doi/10.1103/PhysRevE.91.032118 %R 10.1103/PhysRevE.91.032118 %0 Journal Article %J Physical Review B %D 2014 %T Case study of the uniaxial anisotropic spin-1 bilinear-biquadratic Heisenberg model on a triangular lattice %A Moreno-Cardoner, M. %A Perrin, H. %A Paganelli, S. %A De Chiara, G. %A Sanpera, A. %X 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. %B Physical Review B %V 90 %8 10/2014 %N 14 %! Phys. Rev. B %R 10.1103/PhysRevB.90.144409 %0 Journal Article %J Physical Review E %D 2014 %T Entanglement enhances cooling in microscopic quantum refrigerators %A Nicolas Brunner %A Huber, Marcus %A Noah Linden %A Sandu Popescu %A Ralph Silva %A Paul Skrzypczyk %X 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. %B Physical Review E %V 89 %8 3/2014 %N 3 %! Phys. Rev. E %R 10.1103/PhysRevE.89.032115 %0 Journal Article %J Journal of Statistical Mechanics: Theory and Experiment %D 2014 %T Entanglement properties of spin models in triangular lattices %A Moreno-Cardoner, M. %A Paganelli, S. %A De Chiara, G. %A Sanpera, A. %X 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. %B Journal of Statistical Mechanics: Theory and Experiment %V 2014 %P P10008 %8 10/2014 %N 10 %! J. Stat. Mech. %R 10.1088/1742-5468/2014/10/P10008 %0 Journal Article %J Nature Communications %D 2014 %T Interface between path and orbital angular momentum entanglement for high-dimensional photonic quantum information %A Robert Fickler %A Radek Lapkiewicz %A Huber, Marcus %A Lavery, Martin P.J. %A Padgett, Miles J. %A Anton Zeilinger %X 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. %B Nature Communications %V 5 %8 7/2014 %! Nat Comms %R 10.1038/ncomms5502 %0 Journal Article %J Physical Review A %D 2014 %T Long-range multipartite entanglement close to a first-order quantum phase transition %A Stasińska, J. %A Rogers, B. %A M. Paternostro %A De Chiara, G. %A Sanpera, A. %X 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. %B Physical Review A %V 89 %8 3/2014 %N 3 %! Phys. Rev. A %R 10.1103/PhysRevA.89.032330 %0 Journal Article %J New Journal of Physics %D 2014 %T Quantumness of correlations, quantumness of ensembles and quantum data hiding %A Piani, M %A Narasimhachar, V %A Calsamiglia, John %B New Journal of Physics %V 16 %P 113001 %G eng %U http://stacks.iop.org/1367-2630/16/i=11/a=113001?key=crossref.9f5154f8c85e7f9471e2931d9a02df88 %R 10.1088/1367-2630/16/11/113001 %0 Journal Article %J Physical Review Letters %D 2013 %T Bose-Glass Phases of Ultracold Atoms due to Cavity Backaction %A Hessam Habibian %A André Winter %A Paganelli, Simone %A Heiko Rieger %A Giovanna Morigi %X 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. %B Physical Review Letters %V 110 %8 2/2013 %U http://prl.aps.org/abstract/PRL/v110/i7/e075304 %N 7 %! Phys. Rev. Lett. %R 10.1103/PhysRevLett.110.075304 %0 Journal Article %J Physical Review A %D 2013 %T Entangled singularity patterns of photons in {Ince}-{Gauss} modes %A Krenn, Mario %A Robert Fickler %A Huber, Marcus %A Radek Lapkiewicz %A Plick, William %A Ramelow, Sven %A Anton Zeilinger %B Physical Review A %V 87 %8 jan %G eng %U http://link.aps.org/doi/10.1103/PhysRevA.87.012326 %R 10.1103/PhysRevA.87.012326 %0 Journal Article %J Physical Review Letters %D 2013 %T Entanglement Generation is Not Necessary for Optimal Work Extraction %A Hovhannisyan, Karen %A Martí Perarnau-Llobet %A Huber, Marcus %A Acín, Antonio %X 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. %B Physical Review Letters %V 111 %8 12/2013 %N 24 %! Phys. Rev. Lett. %R 10.1103/PhysRevLett.111.240401 %0 Journal Article %J Physical Review A %D 2013 %T Entropy vector formalism and the structure of multidimensional entanglement in multipartite systems %A Huber, Marcus %A Martí Perarnau-Llobet %A de Vicente, Julio I. %B Physical Review A %V 88 %8 10/2013 %U http://arxiv.org/abs/1307.3541 %N 4 %! Phys. Rev. A %R 10.1103/PhysRevA.88.042328 %0 Journal Article %J Phyiscal Review A %D 2013 %T Quantum phases of incommensurate optical lattices due to cavity backaction %A Hessam Habibian %A André Winter %A Paganelli, Simone %A Heiko Rieger %A Giovanna Morigi %B Phyiscal Review A %V 88 %P 043618 %0 Journal Article %J Physical Review A %D 2013 %T Routing quantum information in spin chains %A Paganelli, Simone %A Lorenzo, Salvatore %A Apollaro, Tony J. G. %A Plastina, Francesco %A Giorgi, Gian Luca %B Physical Review A %V 87 %8 6/2013 %N 6 %! Phys. Rev. A %R 10.1103/PhysRevA.87.062309 %0 Journal Article %J Physical Review A %D 2013 %T Weak randomness in device-independent quantum key distribution and the advantage of using high-dimensional entanglement %A Huber, Marcus %A Pawłowski, Marcin %B Physical Review A %V 88 %8 9/2013 %N 3 %! Phys. Rev. A %R 10.1103/PhysRevA.88.032309 %0 Journal Article %J New Journal of Physics %D 2012 %T Beyond pure state entanglement for atomic ensembles %A Julia Stasińska %A Paganelli, Simone %A Sanpera, Anna %X We analyze multipartite entanglement between atomic ensembles within quantum matter–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. %B New Journal of Physics %V 14 %P 033034 %U http://stacks.iop.org/1367-2630/14/i=3/a=033034 %R 10.1088/1367-2630/14/3/033034 %0 Journal Article %J Physical Review Letters %D 2012 %T Quantum Memory Assisted Probing of Dynamical Spin Correlations %A O. Romero-Isart %A Rizzi, M. %A Muschik, C. A. %A Polzik, E. S. %A Lewenstein, M. %A Sanpera, A. %X 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. %B Physical Review Letters %V 108 %8 2/2012 %N 6 %! Phys. Rev. Lett. %R 10.1103/PhysRevLett.108.065302 %0 Journal Article %J Physical Review A %D 2012 %T Spin-driven spatial symmetry breaking of spinor condensates in a double well %A Melé-Messeguer, M. %A Paganelli, Simone %A Juliá-Díaz, B. %A Ann Sanpera %A Polls, A. %B Physical Review A %I American Physical Society %V 86 %P 053626 - %8 2012/11/26/ %G eng %U http://link.aps.org/doi/10.1103/PhysRevA.86.053626 %N 5 %0 Journal Article %J Phys. Rev. Lett. %D 2011 %T All Nonclassical Correlations Can Be Activated into Distillable Entanglement %A Piani, Marco %A Gharibian, Sevag %A Adesso, Gerardo %A Calsamiglia, John %A Horodecki, Paweł %A Winter, Andreas %B Phys. Rev. Lett. %I American Physical Society %V 106 %P 220403 %8 Jun %U http://prl.aps.org/abstract/PRL/v106/i22/e220403 %) http://arxiv.org/abs/1103.4032 %R 10.1103/PhysRevLett.106.220403 %0 Journal Article %J International Journal of Quantum Information %D 2011 %T Characterizing quantumness via entanglement creation %A Gharibian, Sevag %A Piani, Marco %A Adesso, Gerardo %A Calsamiglia, John %A Pawel Horodecki %B International Journal of Quantum Information %V 9 %P 1701-1713 %8 05 %U http://arxiv.org/abs/1105.3419 %R 10.1142/S0219749911008258 %0 Journal Article %J ArXiv e-prints %D 2011 %T A continuous-variable formalism for the Faraday atom-light interface %A Stasińska, J. %A Paganelli, Simone %A Rodó, C. %A Sanpera, A. %X 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. %B ArXiv e-prints %G eng %U http://arxiv.org/abs/1007.0403 %0 Journal Article %J Phys. Rev. A %D 2011 %T Disordered spinor Bose-Hubbard model %A Ł{\k a}cki, M. %A Paganelli, Simone %A Ahufinger, V. %A Sanpera, Anna %A Zakrzewski, J. %K Condensed Matter - Other Condensed Matter %K Quantum Physics %X 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. %B Phys. Rev. A %V 83 %P 013605 %G eng %U http://link.aps.org/doi/10.1103/PhysRevA.83.013605 %R 10.1103/PhysRevA.83.013605 %0 Journal Article %J Phys. Rev. A %D 2011 %T Entanglement detection in hybrid optomechanical systems %A De Chiara, Gabriele %A Paternostro, Mauro %A Palma, G. Massimo %X 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. %B Phys. Rev. A %V 83 %P 052324 %U http://link.aps.org/doi/10.1103/PhysRevA.83.052324 %R 10.1103/PhysRevA.83.052324 %0 Journal Article %J Physical Review A %D 2011 %T Quantifying, characterizing, and controlling information flow in ultracold atomic gases %A Haikka, P. %A McEndoo, S. %A De Chiara, G. %A G. M. Palma %A Maniscalco, S. %X 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). %B Physical Review A %V 84 %8 9/2011 %U http://pra.aps.org/abstract/PRA/v84/i3/e031602 %N 3 %! Phys. Rev. A %R 10.1103/PhysRevA.84.031602 %0 Journal Article %J J Low Temp Phys %D 2011 %T Spin Effects in Bose-Glass Phases %A Paganelli, Simone %A Ła̧cki, Mateusz %A Ahufinger, Veronica %A Zakrzewski, Jakub %A Sanpera, Anna %B J Low Temp Phys %V 165 %P 227 %U http://www.springerlink.com/content/10w5036068935773/ %R 10.1007/s10909-011-0392-7 %0 Journal Article %J Phys. Rev. Lett. %D 2010 %T Cold-atom induced control of an opto-mechanical device %A M. Paternostro %A De Chiara, Gabriele %A G. M. Palma %X 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. %B Phys. Rev. Lett. %V 104 %P 243602 %8 06/2010 %U http://link.aps.org/doi/10.1103/PhysRevLett.104.243602 %R 10.1103/PhysRevLett.104.243602 %0 Thesis %B Departament de Físca, Grup de Física Teòria: Informació i fenòmens quàntics %D 2010 %T Discriminació quàntica %A Arnau Pujol %Y Muñoz-Tapia, Ramon %X S'estudia la discriminació de diferents sistemes quàntics. S'analitza el procés de discriminació entre qúbits, i es compara amb la discriminació de mesures projectives. Seguidament, es busquen les condicions en les quals la discriminació entre mesures projectives és perfecta, i es realitza el mateix per a la discriminació de transformacions unitàries, per tal de comparar ambdós resultats. %B Departament de Físca, Grup de Física Teòria: Informació i fenòmens quàntics %I Universitat Autònoma de Barcelona %C Barcelona %V Grau en Física %8 07/2010 %9 BSc Thesis %0 Journal Article %J Phys. Rev. A %D 2010 %T Ion-trap simulation of the quantum phase transition in an exactly solvable model of spins coupled to bosons %A Giorgi, Gian Luca %A Paganelli, Simone %A Galve, Fernando %K Quantum Physics %X 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. %B Phys. Rev. A %V 81 %P 052118 %8 2010 %G eng %R 10.1103/PhysRevA.81.052118 %0 Thesis %B Departament de Físca, Grup de Física Teòria: Informació i fenòmens quàntics %D 2010 %T Localització en xarxes complexes %A Perarnau Llobet, Martí %Y Calsamiglia, John %X En els anys 1950s, P.W. Anderson va suggerir la possibilitat d'un nou fenomen en física de l'estat sòlid: la localització. Aquest fenomen consisteix en que la funció d'ona dels electrons es queda totalment localitzada en l'espai provocant que el material passi de ser un conductor a un aïllant. Ha estat extensament estudiat en xarxes ordenades i és conseqüència de les impureses del material. En aquest treball, pretenem estudiar la localització en xarxes amb naturalesa aleatòria, en particular, en xarxes complexes. La idea bàsica és, tenint en compte que l'aleatorietat de les impureses del material provoca localització, veure si l'aleatorietat en l'estructura del material produeix el mateix efecte. %B Departament de Físca, Grup de Física Teòria: Informació i fenòmens quàntics %I Universitat Autònoma de Barcelona %C Barcelona %V Grau en Física %8 07/2010 %9 BSc Thesis %0 Journal Article %J New. J. Phys. %D 2010 %T Spontaneous nucleation of structural defects in inhomogeneous ion chains %A De Chiara, Gabriele %A del Campo, Adolfo %A G. Morigi %A M. B. Plenio %A A. Retzker %X 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. %B New. J. Phys. %V 12 %P 115003 %8 12/2010 %U http://iopscience.iop.org/1367-2630/12/11/115003?fromSearchPage=true %R 10.1088/1367-2630/12/11/115003 %0 Journal Article %J Phys. Rev. Lett. %D 2010 %T Structural defects in ion crystals by quenching the external potential: the inhomogeneous Kibble-Zurek mechanism %A del Campo, Adolfo %A De Chiara, Gabriele %A G. Morigi %A M. B. Plenio %A A. Retzker %B Phys. Rev. Lett. %V 105 %P 075701 %8 08/2010 %U http://link.aps.org/doi/10.1103/PhysRevLett.105.075701 %R 10.1103/PhysRevLett.105.075701 %0 Journal Article %J Physical Review A (Atomic, Molecular, and Optical Physics) %D 2009 %T Manipulating mesoscopic multipartite entanglement with atom-light interfaces %A Julia Stasińska %A Rodó, Carles %A Paganelli, Simone %A Sanpera, Anna %A Birkl, G. %K atom-photon collisions %K EPR paradox %K measurement theory %K mesoscopic entanglement %K multipartite entanglement %K quantum entanglement %K quantum optics %X 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. ©2009 The American Physical Society %B Physical Review A (Atomic, Molecular, and Optical Physics) %I APS %V 80 %P 062304–8 %8 12/2009 %G eng %U http://link.aps.org/abstract/PRA/v80/e062304 %0 Journal Article %J Fortschritte der Physik %D 2009 %T Optimized electron propagation on a quantum chain by a topological phase %A Paganelli, Simone %A Giorgi, G. L. %A de Pasquale, F. %X 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. %B Fortschritte der Physik %V 57 %P 1094–1102 %G eng %U http://doi.wiley.com/10.1002/prop.200900087 %R 10.1002/prop.200900087 %0 Journal Article %J Physical Review A (Atomic, Molecular, and Optical Physics) %D 2008 %T Manipulation of single-photon states encoded in transverse spatial modes: Possible and impossible tasks %A Calvo, Gabriel F. %A Picon, Antonio %K SU(3) theory %X 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. %B Physical Review A (Atomic, Molecular, and Optical Physics) %V 77 %P 012302–7 %8 01/2008 %G eng %U http://link.aps.org/doi/10.1103/PhysRevA.77.012302 %R 10.1103/PhysRevA.77.012302 %0 Journal Article %J Physical Review Letters %D 2008 %T Measuring the Complete Transverse Spatial Mode Spectrum of a Wave Field %A Calvo, Gabriel F. %A Picon, Antonio %A Zambrini, Roberta %B Physical Review Letters %V 100 %P 173902–4 %8 05/2008 %G eng %U http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf&id=PRLTAO000100000017173902000001&idtype=cvips&prog=normal %R 10.1103/PhysRevLett.100.173902 %0 Journal Article %J Nature Physics %D 2008 %T Quantum non-demolition detection of strongly correlated systems %A Eckert, Kai %A Romero-Isart, Oriol %A Rodriguez, Mirta %A Lewenstein, Maciej %A Polzik, Eugene S. %A Sanpera, Anna %B Nature Physics %V 4 %P 50–54 %8 01/2008 %G eng %U http://www.nature.com/nphys/journal/v4/n1/full/nphys776.html %R 10.1038/nphys776 %0 Journal Article %J Physical Review A (Atomic, Molecular, and Optical Physics) %D 2007 %T Measuring two-photon orbital angular momentum entanglement %A Calvo, Gabriel F. %A Picon, Antonio %A Bramon, Albert %K orbital angular momentum %K quantum entanglement %K quantum optics %B Physical Review A (Atomic, Molecular, and Optical Physics) %V 75 %P 012319–8 %8 01/2007 %G eng %U http://link.aps.org/abstract/PRA/v75/e012319 %R 10.1103/PhysRevA.75.012319 %0 Journal Article %J Physical Review Letters %D 2007 %T Optimal Quantum Estimation of Loss in Bosonic Channels %A Monras, Alex %A Paris, Matteo G. A. %B Physical Review Letters %V 98 %P 160401–4 %8 04/2007 %G eng %U http://link.aps.org/abstract/PRL/v98/e160401 %R 10.1103/PhysRevLett.98.160401 %0 Journal Article %J Physical Review Letters %D 2007 %T Predicting Spinor Condensate Dynamics from Simple Principles %A Moreno-Cardoner, M. %A Mur-Petit, J. %A Guilleumas, M. %A Polls, Artur %A Sanpera, Anna %A Lewenstein, Maciej %K Bose-Einstein condensation %K entropy %B Physical Review Letters %V 99 %P 020404–4 %8 07/2007 %G eng %U http://link.aps.org/abstract/PRL/v99/e020404 %R 10.1103/PhysRevLett.99.020404 %0 Journal Article %J Physical Review Letters %D 2007 %T Quantum Polarization Spectroscopy of Ultracold Spinor Gases %A Eckert, Kai %A Zawitkowski, L. %A Sanpera, Anna %A Lewenstein, Maciej %A Polzik, Eugene S. %B Physical Review Letters %V 98 %P 100404–4 %8 03/2007 %G eng %U http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf&id=PRLTAO000098000010100404000001&idtype=cvips&prog=normal %R 10.1103/PhysRevLett.98.100404 %0 Journal Article %J Optics Letters %D 2007 %T Spin-induced angular momentum switching %A Calvo, Gabriel F. %A Picon, Antonio %K angular momentum %K anisotropic optical materials %K polarization %K polarization-selective devices %K quantum optics %X 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. %B Optics Letters %V 32 %P 838–840 %8 04/2007 %G eng %U http://ol.osa.org/abstract.cfm?URI=ol-32-7-838 %R 10.1364/OL.32.000838 %0 Journal Article %J Physical Review Letters %D 2007 %T Trapped Ion Chain as a Neural Network: Error Resistant Quantum Computation %A Pons, Marisa %A Ahufinger, Veronica %A Wunderlich, Christof %A Sanpera, Anna %A Braungardt, Sibylle %A Sen(De), Aditi %A Sen, Ujjwal %A Lewenstein, Maciej %K neural networks %K quantum computation %B Physical Review Letters %V 98 %P 023003–4 %8 01/2007 %G eng %U http://link.aps.org/abstract/PRL/v98/e023003 %R 10.1103/PhysRevLett.98.023003 %0 Journal Article %J Physical Review A (Atomic, Molecular, and Optical Physics) %D 2006 %T Dynamics of F = 1 [sup 87]Rb condensates at finite temperatures %A Mur-Petit, J. %A Guilleumas, M. %A Polls, Artur %A Sanpera, Anna %A Lewenstein, Maciej %A Bongs, K. %A Sengstock, K. %K atom optics %K atom-photon collisions %K Bose-Einstein condensation %K radiation pressure %K rubidium %K spin dynamics %K vectors %B Physical Review A (Atomic, Molecular, and Optical Physics) %V 73 %P 013629–6 %8 01/2006 %G eng %U http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PLRAAN000073000001013629000001&idtype=cvips&gifs=yes %R 10.1103/PhysRevA.73.013629 %0 Journal Article %J Physical Review A (Atomic, Molecular, and Optical Physics) %D 2006 %T Quantum field theory of photons with orbital angular momentum %A Calvo, Gabriel F. %A Picon, Antonio %A Bagan, Emili %K information theory %K orbital angular momentum %K quantum field theory %K quantum optics %B Physical Review A (Atomic, Molecular, and Optical Physics) %V 73 %P 013805–10 %8 01/2006 %G eng %U http://link.aps.org/abstract/PRA/v73/e013805 %R 10.1103/PhysRevA.73.013805 %0 Journal Article %J Foundations of Physics %D 2006 %T Unitarity as Preservation of Entropy and Entanglement in Quantum Systems %A Hulpke, Florian %A Poulsen, Uffe %A Sanpera, Anna %A Sen(De), Aditi %A Sen, Ujjwal %A Lewenstein, Maciej %X 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 %B Foundations of Physics %V 36 %P 477–499 %8 04/2006 %G eng %U http://www.springerlink.com/content/tjg6r668u462848r/fulltext.pdf %R 10.1007/s10701-005-9035-7 %0 Conference Paper %B Laser Spectroscopy: Proceedings of the XVII International Conference, Aviemore, Scotland UK, 19-24 June 2005 %D 2005 %T Disordered complex systems using cold gases and trapped ions %A Sen(De), Aditi %A Sen, Ujjwal %A Lewenstein, Maciej %A Ahufinger, Veronica %A Pons, Marisa %A Sanpera, Anna %E Hinds, E. A. %E Ferguson, A. %E Riis, E. %B Laser Spectroscopy: Proceedings of the XVII International Conference, Aviemore, Scotland UK, 19-24 June 2005 %I World Scientific %C Singapore %P 158–166 %G eng %U http://arxiv.org/abs/quant-ph/0508018 %0 Journal Article %J Physical Review Letters %D 2004 %T Coherence Properties of Guided-Atom Interferometers %A Kreutzmann, H. %A Poulsen, U. %A Lewenstein, M. %A Dumke, R. %A Ertmer, W. %A Birkl, G. %A Sanpera, A. %B Physical Review Letters %V 92 %G eng %U http://prl.aps.org/abstract/PRL/v92/i16/e163201 %R 10.1103/PhysRevLett.92.163201 %0 Journal Article %J Physical Review A (Atomic, Molecular, and Optical Physics) %D 2004 %T Creation and mobility of discrete solitons in Bose-Einstein condensates %A Ahufinger, Veronica %A Sanpera, Anna %A Pedri, P. %A Santos, L. %A Lewenstein, Maciej %X 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. %B Physical Review A (Atomic, Molecular, and Optical Physics) %I American Physical Society %V 69 %P 053604 %8 05/2004 %G eng %U http://link.aps.org/doi/10.1103/PhysRevA.69.053604 %R 10.1103/PhysRevA.69.053604 %0 Journal Article %J Science (New York, N.Y.) %D 2001 %T Feynman's path-integral approach for intense-laser-atom interactions %A Salieres, P. %A Carre, B. %A Le Deroff, L. %A Grasbon, F. %A Paulus, G. G. %A Walther, H. %A Kopold, R. %A Becker, W. %A Milosevic, D. B. %A Sanpera, A. %A Lewenstein, M. %X 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. %B Science (New York, N.Y.) %V 292 %P 902–5 %G eng %U http://www.sciencemag.org/cgi/content/abstract/292/5518/902 %R 10.1126/science.108836 %0 Journal Article %J {PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES} %D 0 %T {Quantum reference frames and their applications to thermodynamics} %A Popescu, Sandu %A Belen Sainz, Ana %A Short, Anthony J. %A Winter, Andreas %X{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 `Foundations of quantum mechanics and their impact on contemporary society'.}

%B {PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES} %V {376} %8 {JUL 13} %R {10.1098/rsta.2018.0111}