Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session X29: Focus Session: Quantum Information for Quantum Foundations  Information Measures, Entanglement, and Entropies 
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Sponsoring Units: GQI Chair: Mark Byrd, Southern Illinois University Carbondale Room: C148 

X29.00001: ABSTRACT WITHDRAWN 
Thursday, March 24, 2011 2:42PM  2:54PM 
X29.00002: Uncertainty Relation for Smooth Entropies Marco Tomamichel, Renato Renner Uncertainty relations give upper bounds on the accuracy by which the outcomes of two incompatible measurements can be predicted. While the established uncertainty relations apply to cases where the predictions are based on purely classical data (e.g., a description of the system's state before the measurement), an extended relation which remains valid in the presence of quantum information has been proposed recently [Berta et al., Nature Physics 6, 659 (2010)]. Here we generalize this uncertainty relation to one formulated in terms of smooth entropies. Since these entropy measures are related to operational quantities, our uncertainty relation has various applications. As an example, we show that it directly implies security of quantum key distribution protocols. [Preview Abstract] 
Thursday, March 24, 2011 2:54PM  3:06PM 
X29.00003: Inadequacy of von Neumann entropy for characterising extractable work Oscar Dahlsten, Renato Renner, Elisabeth Rieper, Vlatko Vedral The lack of knowledge an observer has about a system limits the amount of work it can extract. This lack of knowledge is normally quantified using the Shannon/von Neumann entropy. We show that this standard approach is, surprisingly, only correct in very specific circumstances. In general one should use the recently developed smooth entropy approach. For many common physical situations, including large but internally correlated systems, the resulting values for the extractable work can deviate arbitrarily from those suggested by the standard approach. (For details see arXiv:0908.0424) [Preview Abstract] 
Thursday, March 24, 2011 3:06PM  3:18PM 
X29.00004: Interpreting quantum discord through quantum state merging Vaibhav Madhok, Animesh Datta We present an operational interpretation of quantum discord based on the quantum state merging protocol. Quantum discord is the markup in the cost of quantum communication in the process of quantum state merging, if one discards relevant prior information. Our interpretation has an intuitive explanation based on the strong subadditivity of von Neumann entropy. We use our result to provide operational interpretations of other quantities like the local purity and quantum deficit. Finally, we discuss in brief some instances where our interpretation is valid in the single copy scenario. [Preview Abstract] 
Thursday, March 24, 2011 3:18PM  3:30PM 
X29.00005: The thermodynamic meaning of negative entropy Lidia del Rio, Renato Renner, Johan Aaberg, Oscar Dahlsten, Vlatko Vedral Landauer's erasure principle states that all irreversible operations, like the erasure of data stored in a system, have an inherent work cost. This work cost depends on our knowledge of the system: the less we know about its state, the more it costs to erase it. Here, we analyse erasure in a general setting, where our information about a system can be quantum mechanical. We show that the work cost of erasure is bounded by the entropy of the system conditioned on that quantum information. Our result implies that conditional entropies, originally introduced in the context of information theory, have a direct thermodynamic significance. Since these entropies can become negative, a particular consequence is that an observer who is strongly correlated to a system may gain work while erasing it. [Preview Abstract] 
Thursday, March 24, 2011 3:30PM  3:42PM 
X29.00006: Operational interpretations of quantum discord Marco Piani, Daniel Cavalcanti, Leandro Aolita, Sergio Boixo, Kavan Modi, Andreas Winter Quantum discord quantifies nonclassical correlations going beyond the standard classification of quantum states into entangled and unentangled ones. Although it has received considerable attention, it still lacks any precise interpretation in terms of some protocol in which quantum features are relevant. Here we give quantum discord its first informationtheoretic operational meaning in terms of entanglement consumption in an \emph{extended quantum state merging} protocol. We further relate the asymmetry of quantum discord with the performance imbalance in quantum state merging and dense coding. [Preview Abstract] 
Thursday, March 24, 2011 3:42PM  3:54PM 
X29.00007: Measures of non classical correlations Matthias Lang, Anil Shaji, Carlton Caves To quantify non classical correlations in a quantum state, much effort has been put into the investigation of entanglement and its properties. It is known, however, that entanglement does not capture all quantum correlations. Several entropic measures of nonclassical correlations beyond entanglement have been proposed, quantum discord being the most popular amongst them. We have developed an entropic framework for formulating such measures. We discuss new measures that emerge from this framework, and relations among the various measures, and we present numerical results for the measures for twoqubit states. [Preview Abstract] 
Thursday, March 24, 2011 3:54PM  4:06PM 
X29.00008: Redundant imprinting of information in nonideal environments: Quantum Darwinism via a noisy channel Michael Zwolak, Haitao Quan, Wojciech Zurek Quantum Darwinism provides an informationtheoretic framework for the emergence of the classical world from the quantum substrate. It recognizes that we  the observers  acquire our information about the ``systems of interest'' indirectly from their imprints on the environment. Objectivity, a key property of the classical world, arises via the proliferation of redundant information into the environment where many observers can then intercept it and independently determine the state of the system. While causing a system to decohere, environments that remain nearly invariant under the Hamiltonian dynamics, such as very mixed states, have a diminished ability to transmit information about the system, yet can still acquire redundant information about the system [1,2]. Our results show that Quantum Darwinism is robust with respect to nonideal initial states of the environment.\\[4pt] [1] M. Z., H. T. Q., W. H. Z., Phys. Rev. Lett. 103, 110402 (2009)\\[0pt] [2] M. Z., H. T. Q., W. H. Z., Phys. Rev. A 81, 062110 (2010) [Preview Abstract] 
Thursday, March 24, 2011 4:06PM  4:18PM 
X29.00009: Quantum Darwinism in an Everyday Environment: Huge Redundancy in Scattered Photons Charles Riedel, Wojciech Zurek We study quantum Darwinismthe redundant recording of information about the preferred states of a decohering system by its environmentfor an object illuminated by a blackbody. In the cases of pointsource, small disk, and isotropic illumination, we calculate the quantum mutual information between the object and its photon environment. We demonstrate that this realistic model exhibits fast and extensive proliferation of information about the object into the environment and results in redundancies orders of magnitude larger than the exactly soluble models considered to date. We also demonstrate a reduced ability to create records as initial environmental mixedness increases, in agreement with previous studies. [Preview Abstract] 
Thursday, March 24, 2011 4:18PM  4:30PM 
X29.00010: Quantum systems as embarrassed colleagues: what do tax evasion and state tomography have in common? Chris Ferrie, Robin BlumeKohout Quantum state estimation (a.k.a. ``tomography'') plays a key role in designing quantum information processors. As a problem, it resembles probability estimation  e.g. for classical coins or dice  but with some subtle and important discrepancies. We demonstrate an improved classical analogue that captures many of these differences: the ``noisy coin.'' Observations on noisy coins are unreliable  much like soliciting sensitive information such as ones tax preparation habits. So, like a quantum system, it cannot be sampled directly. Unlike standard coins or dice, whose worstcase estimation \emph{risk} scales as $1/N$ for all states, noisy coins (and quantum states) have a worstcase risk that scales as $1/\sqrt{N}$ and is overwhelmingly dominated by nearlypure states. The resulting optimal estimation strategies for noisy coins are surprising and counterintuitive. We demonstrate some important consequences for quantum state estimation  in particular, that adaptive tomography can recover the $1/N$ risk scaling of classical probability estimation. [Preview Abstract] 
Thursday, March 24, 2011 4:30PM  4:42PM 
X29.00011: Quantum networks reveal quantum nonlocality Daniel Cavalcanti, Mafalda Almeida, Valerio Scarani, Antonio Acin The results of local measurements on some composite quantum systems cannot be reproduced classically. This impossibility, known as quantum nonlocality, represents a milestone in the foundations of quantum theory. Quantum nonlocality is also a valuable resource for information processing tasks, e.g. quantum communication, quantum key distribution, quantum state estimation, or randomness extraction. Still, deciding if a quantum state is nonlocal remains a challenging problem. Here we introduce a novel approach to this question: we study the nonlocal properties of quantum states when distributed and measured in networks. Using our framework, we show how any oneway entanglement distillable state leads to nonlocal correlations. Then, we prove that nonlocality is a nonadditive resource, which can be activated. There exist states, local at the singlecopy level, that become nonlocal when taking several copies of it. Our results imply that the nonlocality of quantum states strongly depends on the measurement context. [Preview Abstract] 
Thursday, March 24, 2011 4:42PM  4:54PM 
X29.00012: A generalization of Noether's theorem and the informationtheoretic approach to the study of symmetric dynamics Iman Marvian, Robert Spekkens Information theory provides a novel approach to study of the consequences of symmetry of dynamics which goes far beyond the traditional conservation laws and Noether's theorem. The conservation laws are not applicable to the dissipative and open systems. In fact, as we will show, even in the case of closed system dynamics if the state of system is not pure the conservation laws do not capture all the consequences of symmetry. Using information theoretic approach to this problem we introduce new quantities called asymmetry monotones, that if the system is closed they are constant of motion and otherwise, if the system is open, they are always nonincreasing. We also explain how different results in quantum information theory can have nontrivial consequences about the symmetric dynamics of quantum systems. [Preview Abstract] 
Thursday, March 24, 2011 4:54PM  5:06PM 
X29.00013: Closed Systems that Measure Particles Michael Steiner, Ronald Rendell The Measurement Problem has been of fundamental concern since the discovery of Schr\"{o}dinger's equation. We have been developing a framework for which this problem can be considered under the assumption that the particle and detector are jointly considered a closed system. The framework is based on imposing conditions on quantum state evolution that such a closed system meet, including conservation of energy and momentum, nocloning and nosignaling, gauge invariance, and relativity constraints. Another requirement will be presented, which is a quantum mechanical generalization of Newton's first law. Based on these conditions, we will derive and present several new results. [Preview Abstract] 
Thursday, March 24, 2011 5:06PM  5:18PM 
X29.00014: Quantum Theory for a Total System with One Internal Measuring Apparatus Wenge Wang We propose a quantum theory for a total system including one internal measuring apparatus. The theory is based on three basic assumptions and a principle termed the principle of compatible description (PCD). The assumptions are: (i) Physical states of the total system can be associated with vectors in the Hilbert space. (ii) Dynamical evolution of a state vector obeys Schr\"{o} dinger equation. (iii) For a physical state of the total system described by a pure vector, in which a subsystem may play the role of an internal measuring apparatus, when certain stable condition is satisfied, the purevector description may be given a Borntype ensemble interpretation. The PCD states that different descriptions for the same state of the total system must give consistent predictions for results of measurements performed by the internal measuring apparatus. The proposed theory lies at a meeting point of Copenhagen, Everett's relativestate, and consistenthistories interpretations of quantum mechanics. While, it provides something new: For example, the PCD imposes a restriction to vectors that can be associated with physical states, which may effectively break the timereversal symmetry of Schr\"{o}dinger equation. As an application of the theory, we derive a condition under which a twolevel quantum system may have definite properties, such that it may play the essential role of a measuring apparatus. [Preview Abstract] 
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