72,418 research outputs found
Reversible and irreversible evolution of a condensed bosonic gas
We have formulated a kinetic theory for a condensed atomic gas in a trap,
i.e., a generalized Gross-Pitaevskii equation, as well as a quantum-Boltzmann
equation for the normal and anomalous fluctuations [R. Walser et al., Phys.
Rev. A, 59, 3878 (1999)]. In this article, the theory is applied to the case of
an isotropic configuration and we present numerical and analytical results for
the reversible real-time propagation, as well as irreversible evolution towards
equilibrium.Comment: 15 pages RevTeX, 8 figures, reviewed PRA resubmissio
Exact and approximate dynamics of the quantum mechanical O(N) model
We study a quantum dynamical system of N, O(N) symmetric, nonlinear
oscillators as a toy model to investigate the systematics of a 1/N expansion.
The closed time path (CTP) formalism melded with an expansion in 1/N is used to
derive time evolution equations valid to order 1/N (next-to-leading order). The
effective potential is also obtained to this order and its properties
areelucidated. In order to compare theoretical predictions against numerical
solutions of the time-dependent Schrodinger equation, we consider two initial
conditions consistent with O(N) symmetry, one of them a quantum roll, the other
a wave packet initially to one side of the potential minimum, whose center has
all coordinates equal. For the case of the quantum roll we map out the domain
of validity of the large-N expansion. We discuss unitarity violation in the 1/N
expansion; a well-known problem faced by moment truncation techniques. The 1/N
results, both static and dynamic, are also compared to those given by the
Hartree variational ansatz at given values of N. We conclude that late-time
behavior, where nonlinear effects are significant, is not well-described by
either approximation.Comment: 16 pages, 12 figrures, revte
Quantum Kinetic Theory for a Condensed Bosonic Gas
We present a kinetic theory for Bose-Einstein condensation of a weakly
interacting atomic gas in a trap. Starting from first principles, we establish
a Markovian kinetic description for the evolution towards equilibrium. In
particular, we obtain a set of self-consistent master equations for mean
fields, normal densities, and anomalous fluctuations. These kinetic equations
generalize the Gross-Pitaevskii mean-field equations, and merge them
consistently with a quantum-Boltzmann equation approach.Comment: 15 pages, no figures; reviewed version; to be published in PR
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