2,475 research outputs found
Chains of Quasi-Classical Informations for Bipartite Correlations and the Role of Twin Observables
Having the quantum correlations in a general bipartite state in mind, the
information accessible by simultaneous measurement on both subsystems is shown
never to exceed the information accessible by measurement on one subsystem,
which, in turn is proved not to exceed the von Neumann mutual information. A
particular pair of (opposite- subsystem) observables are shown to be
responsible both for the amount of quasi-classical correlations and for that of
the purely quantum entanglement in the pure-state case: the former via
simultaneous subsystem measurements, and the latter through the entropy of
coherence or of incompatibility, which is defined for the general case. The
observables at issue are so-called twin observables. A general definition of
the latter is given in terms of their detailed properties.Comment: 7 pages, Latex2e, selected for the December 2002 issue of the Virtual
Journal of Quantum Informatio
On Conserved Current in Markovian Open Quantum Systems
We reexamine the markovian approximation of local current in open quantum
systems, discussed recently by Gebauer and Car. Our derivation is more
transparent, the proof of current conservation becomes explicit and easy.Comment: 3 page
Quantum Control of Two-Qubit Entanglement Dissipation
We investigate quantum control of the dissipation of entanglement under
environmental decoherence. We show by means of a simple two-qubit model that
standard control methods - coherent or open-loop control - will not in general
prevent entanglement loss. However, we propose a control method utilising a
Wiseman-Milburn feedback/measurement control scheme which will effectively
negate environmental entanglement dissipation.Comment: 11 pages,4 figures, minor correctio
Correlations in optically-controlled quantum emitters
We address the problem of optically controlling and quantifying the
dissipative dynamics of quantum and classical correlations in a set-up of
individual quantum emitters under external laser excitation. We show that both
types of correlations, the former measured by the quantum discord, are present
in the system's evolution even though the emitters may exhibit an early stage
disentanglement. In the absence of external laser pumping,we demonstrate
analytically, for a set of suitable initial states, that there is an entropy
bound for which quantum discord and entanglement of the emitters are always
greater than classical correlations, thus disproving an early conjecture that
classical correlations are greater than quantum correlations. Furthermore, we
show that quantum correlations can also be greater than classical correlations
when the system is driven by a laser field. For scenarios where the emitters'
quantum correlations are below their classical counterparts, an optimization of
the evolution of the quantum correlations can be carried out by appropriately
tailoring the amplitude of the laser field and the emitters' dipole-dipole
interaction. We stress the importance of using the entanglement of formation,
rather than the concurrence, as the entanglement measure, since the latter can
grow beyond the total correlations and thus give incorrect results on the
actual system's degree of entanglement.Comment: 11 pages, 10 figures, this version contains minor modifications; to
appear in Phys. Rev.
Classical Correlations and Entanglement in Quantum Measurements
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.Comment: to appear in Physical Review Letter
The fidelity of general bosonic channels with pure state input
We first derive for the general form of the fidelity for various bosonic
channels. Thereby we give the fidelity of different quantum bosonic channel,
possibly with product input and entangled input respectively, as examples. The
properties of the fidelity are carefully examined.Comment: 3 pages, comments welcom
Pure Stationary States of Open Quantum Systems
Using Liouville space and superoperator formalism we consider pure stationary
states of open and dissipative quantum systems. We discuss stationary states of
open quantum systems, which coincide with stationary states of closed quantum
systems. Open quantum systems with pure stationary states of linear oscillator
are suggested. We consider stationary states for the Lindblad equation. We
discuss bifurcations of pure stationary states for open quantum systems which
are quantum analogs of classical dynamical bifurcations.Comment: 7p., REVTeX
Nonequilibrium entropy production for open quantum systems
We consider open quantum systems weakly coupled to a heat reservoir and
driven by arbitrary time-dependent parameters. We derive exact microscopic
expressions for the nonequilibrium entropy production and entropy production
rate, valid arbitrarily far from equilibrium. By using the two-point energy
measurement statistics for system and reservoir, we further obtain a quantum
generalization of the integrated fluctuation theorem put forward by Seifert
[PRL 95, 040602 (2005)].Comment: 4 pages, 1 figur
Relational physics with real rods and clocks and the measurement problem of quantum mechanics
The use of real clocks and measuring rods in quantum mechanics implies a
natural loss of unitarity in the description of the theory. We briefly review
this point and then discuss the implications it has for the measurement problem
in quantum mechanics. The intrinsic loss of coherence allows to circumvent some
of the usual objections to the measurement process as due to environmental
decoherence.Comment: 19 pages, RevTex, no figure
Asymptotics of Quantum Relative Entropy From Representation Theoretical Viewpoint
In this paper it was proved that the quantum relative entropy can be asymptotically attained by Kullback Leibler divergences of
probabilities given by a certain sequence of POVMs. The sequence of POVMs
depends on , but is independent of the choice of .Comment: LaTeX2e. 8 pages. The title was changed from "Asymptotic Attainment
for Quantum Relative Entropy
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