588 research outputs found

### Quantum kinetic theory of trapped atomic gases

We present a general framework in which we can accurately describe the
non-equilibrium dynamics of trapped atomic gases. This is achieved by deriving
a single Fokker-Planck equation for the gas. In this way we are able to discuss
not only the dynamics of an interacting gas above and below the critical
temperature at which the gas becomes superfluid, but also during the phase
transition itself. The last topic cannot be studied on the basis of the usual
mean-field theory and was the main motivation for our work. To show, however,
that the Fokker-Planck equation is not only of interest for recent experiments
on the dynamics of Bose-Einstein condensation, we also indicate how it can, for
instance, be applied to the study of the collective modes of a condensed Bose
gas.Comment: 12 pages of LaTeX and two postscript figures. Contribution to
NATO-ASI Dynamics: Models and Kinetic Methods for Non-Equilibrium Many-Body
Systems edited by John Karkhec

### Coherent versus Incoherent Dynamics during Bose-Einstein Condensation in Atomic Gases

We review and extend the theory of the dynamics of Bose-Einstein condensation
in weakly interacting atomic gases. We present in a unified way both the
semiclassical theory as well as the full quantum theory. This is achieved by
deriving a Fokker-Planck equation that incorporates both the coherent and
incoherent effects of the interactions in a dilute Bose gas. In first instance
we focus our attention on the nonequilibrium dynamics of a homogeneous Bose gas
with a positive interatomic scattering length. After that we discuss how our
results can be generalized to the inhomogeneous situation that exists in the
present experiments with magnetically trapped alkali gases, and how we can deal
with a negative interatomic scattering length in that case as well. We also
show how to arrive at a discription of the collective modes of the gas that
obeys the Kohn theorem at all temperatures. The theory is based on the
many-body T-matrix approximation throughout, since this approximation has the
correct physical behavior near the critical temperature and also treats the
coherent and incoherent processes taking place in the gas on an equal footing.Comment: In response to referee report I have rewritten the introduction. I
have also added new results for the decay rate of a condensate with negative
scattering length and for the collisionless collective modes of a Bose
condensed atomic gas at nonzero temperature

### Condensed matter physics with trapped atomic Fermi gases

We present an overview of the various phase transitions that we anticipate to
occur in trapped fermionic alkali gases. We also discuss the prospects of
observing these transitions in (doubly) spin-polarized Li-6 and K-40 gases,
which are now actively being studied by various experimental groups around the
world.Comment: 18 pages of LaTeX and 2 postscript figures. Contribution to the
international summer school `Enrico Fermi' on Bose-Einstein condensation in
atomic gases, Varenna 199

### Sweeping a molecular Bose-Einstein condensate across a Feshbach resonance

We consider the dissociation of a molecular Bose-Einstein condensate during a
magnetic-field sweep through a Feshbach resonance that starts on the molecular
side of the resonance and ends on the atomic side. In particular, we determine
the energy distribution of the atoms produced after the sweep. We find that the
shape of the energy distribution strongly depends on the rate of the
magnetic-field sweep, in a manner that is in good agreement with recent
experiments.Comment: 4.2 pages, 4 figure

### Trapped fermionic clouds distorted from the trap shape due to many-body effects

We present a general approach for calculating densities and other local
quantities of trapped Fermi gases, when the cloud shape is distorted with
respect to the trap shape due to global energy considerations. Our approach
provides a consistent way to explore physics beyond the local density
approximation, if this is necessary due to the distortion. We illustrate this
by analyzing in detail experimentally observed distortions in an imbalanced
Fermi mixture in an elongated trap. In particular, we demonstrate in that case
dramatic deviations from ellipsoidal cloud shapes arising from the competition
between surface and bulk energies.Comment: 4+ pages, 3 figures. Formalism for distorted trapped fermi systems +
treatment of polarized fermion experiments. Version 2: slightly shortened,
published versio

### Renormalization Group Theory of the Three-Dimensional Dilute Bose Gas

We study the three-dimensional atomic Bose gas using renormalization group
techniques. Using our knowledge of the microscopic details of the interatomic
interaction, we determine the correct initial values of our renormalization
group equations and thus obtain also information on nonuniversal properties. As
a result, we can predict for instance the critical temperature of the gas and
the superfluid and condensate density of the Bose-Einstein condensed phase in
the regime $na\Lambda_{th}^2\ll 1$.Comment: 48 pages of ReVTeX and 13 postscript figures. Submitted for
publication in Physical Review

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