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 {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 {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. ASocial 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 {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 {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 {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 {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 {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 {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 {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 {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 {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 {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 {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 {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 {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 {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 {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 {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} } @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} } @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 {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 {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 {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 {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 {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 {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 {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 {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} } @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} } @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 {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 {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 {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 {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 {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 {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 {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 {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 {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.} } @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} }