2,522 research outputs found
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
Conditions for strictly purity-decreasing quantum Markovian dynamics
The purity, Tr(rho^2), measures how pure or mixed a quantum state rho is. It
is well known that quantum dynamical semigroups that preserve the identity
operator (which we refer to as unital) are strictly purity-decreasing
transformations. Here we provide an almost complete characterization of the
class of strictly purity-decreasing quantum dynamical semigroups. We show that
in the case of finite-dimensional Hilbert spaces a dynamical semigroup is
strictly purity-decreasing if and only if it is unital, while in the infinite
dimensional case, unitality is only sufficient.Comment: 4 pages, no figures. Contribution to the special issue "Real-time
dynamics in complex quantum systems" of Chemical Physics in honor of Phil
Pechukas. v2: Simplified proof of theorem 1 and validity conditions clarifie
Quantum ratchets in dissipative chaotic systems
Using the method of quantum trajectories we study a quantum chaotic
dissipative ratchet appearing for particles in a pulsed asymmetric potential in
the presence of a dissipative environment. The system is characterized by
directed transport emerging from a quantum strange attractor. This model
exhibits, in the limit of small effective Planck constant, a transition from
quantum to classical behavior, in agreement with the correspondence principle.
We also discuss parameter values suitable for implementation of the quantum
ratchet effect with cold atoms in optical lattices.Comment: Significant changes: Several text improvements and new results.
Figure 2 modified. Figure 4 adde
Models for local ohmic quantum dissipation
We construct model master equations for local quantum dissipation. The master
equations are in the form of Lindblad generators, with imposed constraints that
the dissipations be strictly linear (i.e. ohmic), isotropic and translationally
invariant. A particular form for is chosen to satisfy the constraints. The
resulting master equations are given in both the Schr\"odinger and Heisenberg
forms. We obtain fluctuation-dissipation relations, and discuss the relaxation
of average kinetic energy to effective thermal equilibrium values. We compare
our results to the Dekker and the Caldeira-Leggett master equations. These
master equations allow a more general approach to quantum dissipation and the
dynamics of quantum coherence to account for the nontrivial system-environment
coupling in a local environment.Comment: 19 pages, REVTEX, PSU/TH/12
Quantum decoherence in the theory of open systems
In the framework of the Lindblad theory for open quantum systems, we
determine the degree of quantum decoherence of a harmonic oscillator
interacting with a thermal bath. It is found that the system manifests a
quantum decoherence which is more and more significant in time. We calculate
also the decoherence time scale and analyze the transition from quantum to
classical behaviour of the considered system.Comment: 6 pages; talk at the 3rd International Workshop "Quantum Physics and
Communication" (QPC 2005), Dubna, Russia, 200
On the quantum, classical and total amount of correlations in a quantum state
We give an operational definition of the quantum, classical and total amount
of correlations in a bipartite quantum state. We argue that these quantities
can be defined via the amount of work (noise) that is required to erase
(destroy) the correlations: for the total correlation, we have to erase
completely, for the quantum correlation one has to erase until a separable
state is obtained, and the classical correlation is the maximal correlation
left after erasing the quantum correlations.
In particular, we show that the total amount of correlations is equal to the
quantum mutual information, thus providing it with a direct operational
interpretation for the first time. As a byproduct, we obtain a direct,
operational and elementary proof of strong subadditivity of quantum entropy.Comment: 12 pages ReVTeX4, 2 eps figures. v2 has some arguments clarified and
references update
Structure of the Algebra of Effective Observables in Quantum Mechanics
A subclass of dynamical semigroups induced by the interaction of a quantum
system with an environment is introduced. Such semigroups lead to the selection
of a stable subalgebra of effective observables. The structure of this
subalgebra is completely determined
Quantum decoherence of the damped harmonic oscillator
In the framework of the Lindblad theory for open quantum systems, we
determine the degree of quantum decoherence of a harmonic oscillator
interacting with a thermal bath. It is found that the system manifests a
quantum decoherence which is more and more significant in time. We also
calculate the decoherence time and show that it has the same scale as the time
after which thermal fluctuations become comparable with quantum fluctuations.Comment: Talk at the XI International Conference on Quantum Optics
(ICQO'2006), May 2006, Minsk (Belarus), 9 page
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