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Search Results: 1 - 10 of 130559 matches for " V. Vedral "
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Entanglement in The Second Quantization Formalism
V. Vedral
Physics , 2003, DOI: 10.2478/BF02476298
Abstract: We study properties of entangled systems in the (mainly non-relativistic) second quantization formalism. This is then applied to interacting and non-interacting bosons and fermions and the differences between the two are discussed. We present a general formalism to show how entanglement changes with the change of modes of the system. This is illustrated with examples such as the Bose condensation and the Unruh effect. It is then shown that a non-interacting collection of fermions at zero temperature can be entangled in spin providing that their distances do not exceed the inverse Fermi wavenumber. Beyond this distance all bipartite entanglement vanishes, although classical correlations still persist. We compute the entanglement of formation as well as the mutual information for two spin-correlated electrons as a function of their distance. The analogous non-interacting collection of bosons displays no entanglement in the internal degrees of freedom. We show how to generalize our analysis of the entanglement in the internal degrees of freedom to an arbitrary number of particles.
Classical Correlations and Entanglement in Quantum Measurements
V. Vedral
Physics , 2002, DOI: 10.1103/PhysRevLett.90.050401
Abstract: We analyze a quantum measurement where the apparatus is initially in a mixed state. We show that the amount of information gained in a measurement is not equal to the amount of entanglement between the system and the apparatus, but is instead equal to the degree of classical correlations between the two. As a consequence, we derive an uncertainty-like expression relating the information gain in the measurement and the initial mixedness of the apparatus. Final entanglement between the environment and the apparatus is also shown to be relevant for the efficiency of the measurement.
The Role of Relative Entropy in Quantum Information Theory
V. Vedral
Physics , 2001, DOI: 10.1103/RevModPhys.74.197
Abstract: Quantum mechanics and information theory are among the most important scientific discoveries of the last century. Although these two areas initially developed separately it has emerged that they are in fact intimately related. In this review I will show how quantum information theory extends traditional information theory by exploring the limits imposed by quantum, rather than classical mechanics on information storage and transmission. The derivation of many key results uniquely differentiates this review from the "usual" presentation in that they are shown to follow logically from one crucial property of relative entropy. Within the review optimal bounds on the speed-up that quantum computers can achieve over their classical counter-parts are outlined using information theoretic arguments. In addition important implications of quantum information theory to thermodynamics and quantum measurement are intermittently discussed. A number of simple examples and derivations including quantum super-dense coding, quantum teleportation, Deutsch's and Grover's algorithms are also included.
Landauer's erasure, error correction and entanglement
V. Vedral
Physics , 1999, DOI: 10.1098/rspa.2000.0545
Abstract: Classical and quantum error correction are presented in the form of Maxwell's demon and their efficiency analyzed from the thermodynamic point of view. We explain how Landauer's principle of information erasure applies to both cases. By then extending this principle to entanglement manipulations we rederive upper bounds on purification procedures thereby linking the ''no local increase of entanglement'' principle to the Second Law of thermodynamics.
On bound entanglement assisted distillation
V. Vedral
Physics , 1999, DOI: 10.1016/S0375-9601(99)00686-6
Abstract: We investigate asymptotic distillation of entanglement in the presence of an unlimited amount of bound entanglement for bi-partite systems. We show that the distillability is still bounded by the relative entropy of entanglement. This offers a strong support to the fact that bound entanglement does not improve distillation of entanglement.
Entanglement Production in Non-Equilibrium Thermodynamics
V. Vedral
Physics , 2007,
Abstract: We define and analyse the concept of entanglement production during the evolution of a general quantum mechanical dissipative system. While it is important to minimise entropy production in order to achieve thermodynamical efficiency, maximising the rate of change of entanglement is important in quantum information processing. Quantitative relations are obtained between entropy and entanglement productions, under specific assumptions detailed in the text. We apply these to the processes of dephasing and decay of correlations between two initially entangled qubits. Both the Master equation treatment as well as the higher Hilbert space analysis are presented. Our formalism is very general and contains as special cases many reported individual instance of entanglement dynamics, such as, for example, the recently discovered notion of the sudden death of entanglement.
Local extraction of EPR entanglement from classical systems
D. Kaszlikowski,V. Vedral
Physics , 2006,
Abstract: Coherent states with large amplitudes are traditionally thought of as the best quantum mechanical approximation of classical behavior. Here we argue that, far from being classical, coherent state are in fact highly entangled. We demonstrate this by showing that a general system of indistinguishable bosons in a coherent state can be used to entangle, by local interactions, two spatially separated and distinguishable non-interacting quantum systems. Entanglement can also be extracted in the same way from number states or any other nontrivial superpositions of them.
Information, Relative Entropy of Entanglement and Irreversibility
L. Henderson,V. Vedral
Physics , 1999, DOI: 10.1103/PhysRevLett.84.10
Abstract: Previously proposed measures of entanglement, such as entanglement of formation and assistance, are shown to be special cases of the relative entropy of entanglement. The difference between these measures for an ensemble of mixed states is shown to depend on the availability of classical information about particular members of the ensemble. Based on this, relations between relative entropy of entanglement and mutual information are derived.
Classicality of spin-coherent states via entanglement and distinguishability
D. Markham,V. Vedral
Physics , 2002, DOI: 10.1103/PhysRevA.67.042113
Abstract: We investigate the classical nature of the spin coherent states. In addition to being minimum uncertainty states, as the size of the spin, S, increases, the classical nature is seen to increase in two respects: in their resistance to entanglement generation (when passed through a beam splitter) and in the distinguishability of the states. In the infinite S limit the spin coherent state is a subclass of the optical coherent states (namely the subclass of orthogonal optical coherent states). These states generate no entanglement and are obviously completely distinguishable. The decline of the generated entanglement, and in this sense increase in classicality with S, is very slow and dependent on the amplitude z of the state. Surprisingly we find that for |z| > 1 there is an initial increase in entanglement followed by an extremely gradual decline to zero. The distinguishability, on the other hand, quickly becomes classical for all z. We illustrate the distinguishability of spin coherent states in a novel manner using the representation of Majorana.
Classical, quantum and total correlations
L. Henderson,V. Vedral
Physics , 2001, DOI: 10.1088/0305-4470/34/35/315
Abstract: We discuss the problem of separating consistently the total correlations in a bipartite quantum state into a quantum and a purely classical part. A measure of classical correlations is proposed and its properties are explored.
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