20 research outputs found
PGPE theory of finite temperature collective modes for a trapped Bose gas
We develop formalism based on the projected Gross Pitaevskii equation to
simulate the finite temperature collective mode experiments of Jin et al. [PRL
78, 764 (1997)]. We examine the and quadrupolar modes on the
temperature range and calculate the frequencies of, and phase
between, the condensate and noncondensate modes, and the condensate mode
damping rate. This study is the first quantitative comparison of the projected
Gross-Pitaevskii equation to experimental results in a dynamical regime.Comment: 15 pages, 16 figure
Turbulence in Binary Bose-Einstein Condensates Generated by Highly Non-Linear Rayleigh-Taylor and Kelvin-Helmholtz Instabilities
Quantum turbulence (QT) generated by the Rayleigh-Taylor instability in
binary immiscible ultracold 87Rb atoms at zero temperature is studied
theoretically. We show that the quantum vortex tangle is qualitatively
different from previously considered superfluids, which reveals deep relations
between QT and classical turbulence. The present QT may be generated at
arbitrarily small Mach numbers, which is a unique property not found in
previously studied superfluids. By numerical solution of the coupled
Gross-Pitaevskii equations we find that the Kolmogorov scaling law holds for
the incompressible kinetic energy. We demonstrate that the phenomenon may be
observed in the laboratory.Comment: Revised version. 7 pages, 8 figure
Degenerate Fermi gas in a combined harmonic-lattice potential
In this paper we derive an analytic approximation to the density of states
for atoms in a combined optical lattice and harmonic trap potential as used in
current experiments with quantum degenerate gases. We compare this analytic
density of states to numerical solutions and demonstrate its validity regime.
Our work explicitly considers the role of higher bands and when they are
important in quantitative analysis of this system. Applying our density of
states to a degenerate Fermi gas we consider how adiabatic loading from a
harmonic trap into the combined harmonic-lattice potential affects the
degeneracy temperature. Our results suggest that occupation of excited bands
during loading should lead to more favourable conditions for realizing
degenerate Fermi gases in optical lattices.Comment: 11 pages, 9 figure
Interaction effects on dynamic correlations in non-condensed Bose gases
We consider dynamic, i.e., frequency-dependent, correlations in non-condensed
ultracold atomic Bose gases. In particular, we consider the single-particle
correlation function and its power spectrum. We compute this power spectrum for
a one-component Bose gas, and show how it depends on the interatomic
interactions that lead to a finite single-particle relaxation time. As another
example, we consider the power spectrum of spin-current fluctuations for a
two-component Bose gas and show how it is determined by the spin-transport
relaxation time.Comment: 9 pages, 3 figure
Two point correlations of a trapped interacting Bose gas at finite temperature
We develop a computationally tractable method for calculating correlation
functions of the finite temperature trapped Bose gas that includes the effects
of s-wave interactions. Our approach uses a classical field method to model the
low energy modes and treats the high energy modes using a Hartree-Fock
description. We present results of first and second order correlation
functions, in position and momentum space, for an experimentally realistic
system in the temperature range of to . We also characterize
the spatial coherence length of the system. Our theory should be applicable in
the critical region where experiments are now able to measure first and second
order correlations.Comment: 9 pages, 4 figure
Thermodynamics of quantum degenerate gases in optical lattices
The entropy-temperature curves are calculated for non-interacting Bose and
Fermi gases in a 3D optical lattice. These curves facilitate understanding of
how adiabatic changes in the lattice depth affect the temperature, and we
demonstrate regimes where the atomic sample can be significantly heated or
cooled by the loading process. We assess the effects of interactions on a Bose
gas in a deep optical lattice, and show that interactions ultimately limit the
extent of cooling that can occur during lattice loading.Comment: 6 pages, 4 figures. Submitted to proceedings of Laser Physics 2006
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Parametric resonance of capillary waves at the interface between two immiscible Bose-Einstein condensates
We study parametric resonance of capillary waves on the interface between two
immiscible Bose-Einstein condensates pushed towards each other by an
oscillating force. Guided by analytical models, we solve numerically the
coupled Gross-Pitaevskii equations for two-component Bose-Einstein condensate
at zero temperature. We show that, at moderate amplitudes of the driving force,
the instability is stabilized due to non-linear modifications of the
oscillation frequency. When the amplitude of the driving force is large enough,
we observe detachment of droplets from the Bose-Einstein condensates, resulting
in generation of quantum vortices (skyrmions). We analytically investigate the
vortex dynamics, and conditions of quantized vortex generation.Comment: (Version 2) 11 resized figures. One new reference adde
Temporal correlations of elongated Bose gases at finite temperature
Temporal correlations in the harmonically trapped finite temperature Bose gas
are studied through the calculation of appropriate phase correlation functions.
A wide parameter regime is covered to ascertain the role that temperature
fluctuations and trap geometry play in the temporal coherence of the 1D to 3D
crossover region. Bogoliubov analysis is used to establish results in the 1D
and spherical limits. Formalism is then developed using the projected
Gross-Pitaevskii equation to calculate correlation functions in 3D simulations
of varying trap elongation and temperature.Comment: 8 pages, 5 figure