649 research outputs found
Quantum thermodynamics of systems with anomalous dissipative coupling
The standard {\em system-plus-reservoir} approach used in the study of
dissipative systems can be meaningfully generalized to a dissipative coupling
involving the momentum, instead of the coordinate: the corresponding equation
of motion differs from the Langevin equation, so this is called {\em anomalous}
dissipation. It occurs for systems where such coupling can indeed be derived
from the physical analysis of the degrees of freedom which can be treated as a
dissipation bath. Starting from the influence functional corresponding to
anomalous dissipation, it is shown how to derive the effective classical
potential that gives the quantum thermal averages for the dissipative system in
terms of classical-like calculations; the generalization to many degrees of
freedom is given. The formalism is applied to a single particle in a
double-well and to the discrete model. At variance with the standard
case, the fluctuations of the coordinate are enhanced by anomalous dissipative
coupling.Comment: 12 pages, 5 figures, to be published in Phys. Rev.
Quantum fluctuations in one-dimensional arrays of condensates
The effects of quantum and thermal fluctuations upon the fringe structure
predicted to be observable in the momentum distribution of coupled
Bose-Einstein condensates are studied by the effective-potential method. For a
double-well trap, the coherence factor recently introduced by Pitaevskii and
Stringari [Phys. Rev. Lett. 87, 180402 (2001)] is calculated using the
effective potential approach and is found in good agreement with their result.
The calculations are extended to the case of a one-dimensional array of
condensates, showing that quantum effects are essentially described through a
simple renormalization of the energy scale in the classical analytical
expression for the fringe structure. The consequences for the experimental
observability are discussed.Comment: RevTeX, 4 pages, 5 eps figures (published version with updated
references
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