2,034 research outputs found
Entropic Bell inequalities
We derive entropic Bell inequalities from considering entropy Venn diagrams. These entropic inequalities, akin to the Braunstein-Caves inequalities, are violated for a quantum-mechanical Einstein-Podolsky-Rosen pair, which implies that the conditional entropies of Bell variables must be negative in this case. This suggests that the satisfaction of entropic Bell inequalities is equivalent to the non-negativity of conditional entropies as a necessary condition for separability
On the von Neumann capacity of noisy quantum channels
We discuss the capacity of quantum channels for information transmission and
storage. Quantum channels have dual uses: they can be used to transmit known
quantum states which code for classical information, and they can be used in a
purely quantum manner, for transmitting or storing quantum entanglement. We
propose here a definition of the von Neumann capacity of quantum channels,
which is a quantum mechanical extension of the Shannon capacity and reverts to
it in the classical limit. As such, the von Neumann capacity assumes the role
of a classical or quantum capacity depending on the usage of the channel. In
analogy to the classical construction, this capacity is defined as the maximum
von Neumann mutual entropy processed by the channel, a measure which reduces to
the capacity for classical information transmission through quantum channels
(the "Kholevo capacity") when known quantum states are sent. The quantum mutual
entropy fulfills all basic requirements for a measure of information, and
observes quantum data-processing inequalities. We also derive a quantum Fano
inequality relating the quantum loss of the channel to the fidelity of the
quantum code. The quantities introduced are calculated explicitly for the
quantum "depolarizing" channel. The von Neumann capacity is interpreted within
the context of superdense coding, and an "extended" Hamming bound is derived
that is consistent with that capacity.Comment: 15 pages RevTeX with psfig, 13 figures. Revised interpretation of
capacity, added section, changed titl
Prolegomena to a non-equilibrium quantum statistical mechanics
We suggest that the framework of quantum information theory, which has been
developing rapidly in recent years due to intense activity in quantum
computation and quantum communication, is a reasonable starting point to study
non-equilibrium quantum statistical phenomena. As an application, we discuss
the non-equilibrium quantum thermodynamics of black hole formation and
evaporation.Comment: 20 pages, LaTeX with elsart.cls, 8 postscript figures. Special issue
on quantum computation of Chaos, Solitons, and Fractal
Tipstreaming of a drop in simple shear flow in the presence of surfactant
We have developed a multi-phase SPH method to simulate arbitrary interfaces
containing surface active agents (surfactants) that locally change the
properties of the interface, such the surface tension coefficient. Our method
incorporates the effects of surface diffusion, transport of surfactant from/to
the bulk phase to/from the interface and diffusion in the bulk phase.
Neglecting transport mechanisms, we use this method to study the impact of
insoluble surfactants on drop deformation and breakup in simple shear flow and
present the results in a fluid dynamics video.Comment: Two videos are included for the Gallery of Fluid Motion of the APS
DFD Meeting 201
Reduction criterion for separability
We introduce a separability criterion based on the positive map Γ:ρ→(Tr ρ)-ρ, where ρ is a trace-class Hermitian operator. Any separable state is mapped by the tensor product of Γ and the identity into a non-negative operator, which provides a simple necessary condition for separability. This condition is generally not sufficient because it is vulnerable to the dilution of entanglement. In the special case where one subsystem is a quantum bit, Γ reduces to time reversal, so that this separability condition is equivalent to partial transposition. It is therefore also sufficient for 2×2 and 2×3 systems. Finally, a simple connection between this map for two qubits and complex conjugation in the “magic” basis [Phys. Rev. Lett. 78, 5022 (1997)] is displayed
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