419 research outputs found
Asymptotic Entanglement and Lindblad Dynamics: a Perturbative Approach
We consider an open bipartite quantum system with dissipative Lindblad type
dynamics. In order to study the entanglement of the stationary states, we
develop a perturbative approach and apply it to the physically significant case
when a purely dissipative perturbation is added to the unperturbed generator
which by itself would produce reversible unitary dynamics.Comment: 15 page
Open Quantum Dynamics: Complete Positivity and Entanglement
We review the standard treatment of open quantum systems in relation to
quantum entanglement, analyzing, in particular, the behaviour of bipartite
systems immersed in a same environment. We first focus upon the notion of
complete positivity, a physically motivated algebraic constraint on the quantum
dynamics, in relation to quantum entanglement, i.e. the existence of
statistical correlations which can not be accounted for by classical
probability. We then study the entanglement power of heat baths versus their
decohering properties, a topic of increasing importance in the framework of the
fast developing fields of quantum information, communication and computation.
The presentation is self contained and, through several examples, it offers a
detailed survey of the physics and of the most relevant and used techniques
relative to both quantum open system dynamics and quantum entanglement.Comment: LaTex, 77 page
Planck's scale dissipative effects in atom interferometry
Atom interferometers can be used to study phenomena leading to
irreversibility and dissipation, induced by the dynamics of fundamental objects
(strings and branes) at a large mass scale. Using an effective, but physically
consistent description in terms of a master equation of Lindblad form, the
modifications of the interferometric pattern induced by the new phenomena are
analyzed in detail. We find that present experimental devices can in principle
provide stringent bounds on the new effects.Comment: 12 pages, plain-Te
Dissipation and decoherence in photon interferometry
The propagation of polarized photons in optical media can be effectively
modeled by means of quantum dynamical semigroups. These generalized time
evolutions consistently describe phenomena leading to loss of phase coherence
and dissipation originating from the interaction with a large, external
environment. High sensitive experiments in the laboratory can provide stringent
bounds on the fundamental energy scale that characterizes these non-standard
effects.Comment: 14 pages, plain-Te
Joint reality and Bell inequalities for consecutive measurements
Some new Bell inequalities for consecutive measurements are deduced under
joint realism assumption, using some perfect correlation property. No locality
condition is needed. When the measured system is a macroscopic system, joint
realism assumption substitutes the non-invasive hypothesis advantageously,
provided that the system satisfies the perfect correlation property. The new
inequalities are violated quantically. This violation can be expected to be
more severe than in the case of precedent temporal Bell inequalities. Some
microscopic and mesoscopic situations, in which the new inequalities could be
tested, are roughly considered.Comment: 7 pages, no figure
Effective dissipative dynamics for polarized photons
In the framework of open quantum systems, the propagation of polarized
photons can be effectively described using quantum dynamical semigroups. These
extended time-evolutions induce irreversibility and dissipation. Planned, high
sensitive experiments, both in the laboratory and in space, will be able to put
stringent bounds on these non-standard effects.Comment: 15 pages, plain-TeX, no figure
Quantum Dissipative Effects and Neutrinos : current constraints and future perspectives
We establish the most stringent experimental constraints coming from recent
terrestrial neutrino experiments on quantum mechanical decoherence effects in
neutrino systems. Taking a completely phenomenological approach, we probe
vacuum oscillations plus quantum decoherence between two neutrino species in
the channels , and , admitting that the quantum decoherence parameter is related
to the neutrino energy as : ,
with and 2. Our bounds are valid for a neutrino mass squared
difference compatible with the atmospheric, the solar and, in many cases, the
LSND scale. We also qualitatively discuss the perspectives of the future long
baseline neutrino experiments to further probe quantum dissipation.Comment: 26 pages, 8 encapsulated postscript figure
Probing possible decoherence effects in atmospheric neutrino oscillations
It is shown that the results of the Super-Kamiokande atmospheric neutrino
experiment, interpreted in terms of nu_munu_tau flavor transitions, can
probe possible decoherence effects induced by new physics (e.g., by quantum
gravity) with high sensitivity, supplementing current laboratory tests based on
kaon oscillations and on neutron interferometry. By varying the (unknown)
energy dependence of such effects, one can either obtain strong limits on their
amplitude, or use them to find an unconventional solution to the atmospheric nu
anomaly based solely on decoherence.Comment: Title changed; major changes in the text; includes the discussion of
a new solution to the atmosheric neutrino anomaly, based on decoherence; a
second figure and a note have been adde
Information-theoretical meaning of quantum dynamical entropy
The theory of noncommutative dynamical entropy and quantum symbolic dynamics
for quantum dynamical systems is analised from the point of view of quantum
information theory. Using a general quantum dynamical system as a communication
channel one can define different classical capacities depending on the
character of resources applied for encoding and decoding procedures and on the
type of information sources. It is shown that for Bernoulli sources the
entanglement-assisted classical capacity, which is the largest one, is bounded
from above by the quantum dynamical entropy defined in terms of operational
partitions of unity. Stronger results are proved for the particular class of
quantum dynamical systems -- quantum Bernoulli shifts. Different classical
capacities are exactly computed and the entanglement-assisted one is equal to
the dynamical entropy in this case.Comment: 6 page
Complete positivity of nonlinear evolution: A case study
Simple Hartree-type equations lead to dynamics of a subsystem that is not
completely positive in the sense accepted in mathematical literature. In the
linear case this would imply that negative probabilities have to appear for
some system that contains the subsystem in question. In the nonlinear case this
does not happen because the mathematical definition is physically unfitting as
shown on a concrete example.Comment: extended version, 3 appendices added (on mixed states, projection
postulate, nonlocality), to be published in Phys. Rev.
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