493,767 research outputs found
Quantum data processing and error correction
This paper investigates properties of noisy quantum information channels. We
define a new quantity called {\em coherent information} which measures the
amount of quantum information conveyed in the noisy channel. This quantity can
never be increased by quantum information processing, and it yields a simple
necessary and sufficient condition for the existence of perfect quantum error
correction.Comment: LaTeX, 20 page
Quantum fluctuation theorems for arbitrary environments: adiabatic and non-adiabatic entropy production
We analyze the production of entropy along non-equilibrium processes in
quantum systems coupled to generic environments. First, we show that the
entropy production due to final measurements and the loss of correlations obeys
a fluctuation theorem in detailed and integral forms. Second, we discuss the
decomposition of the entropy production into two positive contributions,
adiabatic and non-adiabatic, based on the existence of invariant states of the
local dynamics. Fluctuation theorems for both contributions hold only for
evolutions verifying a specific condition of quantum origin. We illustrate our
results with three relevant examples of quantum thermodynamic processes far
from equilibrium.Comment: 20 pages + 6 of appendices; 7 figures; v2: New example added (example
A) and some minor corrections; accepted in Phys. Rev.
When is Quantum Decoherence Dynamics Classical?
A direct classical analog of quantum decoherence is introduced. Similarities
and differences between decoherence dynamics examined quantum mechanically and
classically are exposed via a second-order perturbative treatment and via a
strong decoherence theory, showing a strong dependence on the nature of the
system-environment coupling. For example, for the traditionally assumed linear
coupling, the classical and quantum results are shown to be in exact agreement.Comment: 5 pages, no figures, to appear in Physical Review Letter
Energy representation for out-of-equilibrium Brownian-like systems: steady states and fluctuation relations
Stochastic dynamics in the energy representation is employed as a method to
study non-equilibrium Brownian-like systems. It is shown that the equation of
motion for the energy of such systems can be taken in the form of the Langevin
equation with multiplicative noise. Properties of the steady states are
examined by solving the Fokker-Planck equation for the energy distribution
functions. The generalized integral fluctuation theorem is deduced for the
systems characterized by the shifted probability flux operator. There are a
number of entropy and fluctuation relations such as the Hatano-Sasa identity
and the Jarzynski's equality that follow from this theorem.Comment: revtex4-1, 18 pages, extended discussion, references adde
Linear Quantum Entropy and Non-Hermitian Hamiltonians
We consider the description of open quantum systems with probability sinks
(or sources) in terms of general non-Hermitian Hamiltonians.~Within such a
framework, we study novel possible definitions of the quantum linear entropy as
an indicator of the flow of information during the dynamics. Such linear
entropy functionals are necessary in the case of a partially Wigner-transformed
non-Hermitian Hamiltonian (which is typically useful within a mixed
quantum-classical representation). Both the case of a system represented by a
pure non-Hermitian Hamiltonian as well as that of the case of non-Hermitian
dynamics in a classical bath are explicitly considered.Comment: Entropy, Special Issue "Entropy in Quantum Systems and Quantum Field
Theory (QFT)
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