3,431 research outputs found
Effective microscopic models for sympathetic cooling of atomic gases
Thermalization of a system in the presence of a heat bath has been the
subject of many theoretical investigations especially in the framework of
solid-state physics. In this setting, the presence of a large bandwidth for the
frequency distribution of the harmonic oscillators schematizing the heat bath
is crucial, as emphasized in the Caldeira-Leggett model. By contrast, ultracold
gases in atomic traps oscillate at well-defined frequencies and therefore seem
to lie outside the Caldeira-Leggett paradigm. We introduce interaction
Hamiltonians which allow us to adapt the model to an atomic physics framework.
The intrinsic nonlinearity of these models differentiates them from the
original Caldeira-Leggett model and calls for a nontrivial stability analysis
to determine effective ranges for the model parameters. These models allow for
molecular dynamics simulations of mixtures of ultracold gases, which is of
current relevance for optimizing sympathetic cooling in degenerate Bose-Fermi
mixtures.Comment: 14 pages, 7 figure
Variational approach to the Caldeira-Leggett model
We apply the displaced-oscillator variational ansatz to the Caldeira-Leggett
model for a quantum particle in a one-dimensional box described by a
tight-binding chain. We focus on the case of an Ohmic environment and study the
phase diagram for different chain lengths. At zero temperature there is a phase
transition to a localized phase when the number of sites is even. At finite
temperature, a transition from a coherent to an incoherent regime is predicted
for all the chain lengths considered. Finally, the results are compared to
those obtained with numerical techniques.Comment: 7 pages, 4 figure
Effective Microscopic Models for Sympathetic Cooling of Atomic Gases
Thermalization of a system in the presence of a heat bath has been the subject of many theoretical investigations especially in the framework of solid-state physics. In this setting, the presence of a large bandwidth for the frequency distribution of the harmonic oscillators schematizing the heat bath is crucial, as emphasized in the Caldeira-Leggett model. By contrast, ultracold gases in atomic traps oscillate at well-defined frequencies and therefore seem to lie outside the Caldeira-Leggett paradigm. We introduce interaction Hamiltonians which allow us to adapt the model to an atomic physics framework. The intrinsic nonlinearity of these models differentiates them from the original Caldeira-Leggett model and calls for a nontrivial stability analysis to determine effective ranges for the model parameters. These models allow for molecular-dynamics simulations of mixtures of ultracold gases, which is of current relevance for optimizing sympathetic cooling in degenerate Bose-Fermi mixtures
Quantum-classical transition in the Caldeira-Leggett model
The quantum-classical transition in the Caldeira-Leggett model is
investigated in the framework of the functional renormalization group method.
It is shown that a divergent quadratic term arises in the action due to the
heat bath in the model. By removing the divergence with a frequency cutoff we
considered the critical behavior of the model. The critical exponents belonging
to the susceptibility and the correlation length are determined and their
independence of the frequency cutoff and the renormalization scheme is shown.Comment: 8 pages, 4 figure
A Rigorous Approach to the Feynman-Vernon Influence Functional and its Applications. I
A rigorous representation of the Feynman-Vernon influence functional used to describe open quantum systems is given, based on the theory of infinite dimensional oscillatory integrals. An application to the case of the density matrices describing the Caldeira-Leggett model of two quantum systems with a quadratic interaction is treated
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