80 research outputs found
Bose-Einstein condensates in fast rotation
In this short review we present our recent results concerning the rotation of
atomic Bose-Einstein condensates confined in quadratic or quartic potentials,
and give an overview of the field. We first describe the procedure used to set
an atomic gas in rotation and briefly discuss the physics of condensates
containing a single vortex line. We then address the regime of fast rotation in
harmonic traps, where the rotation frequency is close to the trapping
frequency. In this limit the Landau Level formalism is well suited to describe
the system. The problem of the condensation temperature of a fast rotating gas
is discussed, as well as the equilibrium shape of the cloud and the structure
of the vortex lattice. Finally we review results obtained with a quadratic +
quartic potential, which allows to study a regime where the rotation frequency
is equal to or larger than the harmonic trapping frequency.Comment: Laser Physics Letters 2, 275 (2005
Observation of Phase Defects in Quasi-2D Bose-Einstein Condensates
We have observed phase defects in quasi-2D Bose-Einstein condensates close to
the condensation temperature. Either a single or several equally spaced
condensates are produced by selectively evaporating the sites of a 1D optical
lattice. When several clouds are released from the lattice and allowed to
overlap, dislocation lines in the interference patterns reveal nontrivial phase
defects
The atomic Bose gas in Flatland
We describe a recent experiment performed with rubidium atoms (Rb),
aiming at studying the coherence properties of a two-dimensional gas of bosonic
particles at low temperature. We have observed in particular a
Berezinskii--Kosterlitz--Thouless (BKT) type crossover in the system, using a
matter wave heterodyning technique. At low temperatures, the gas is
quasi-coherent on the length scale set by the system size. As the temperature
is increased, the loss of long-range coherence coincides with the onset of the
proliferation of free vortices, in agreement with the microscopic BKT theory.Comment: To appear in "ATOMIC PHYSICS 20" Proceedings of the XX International
Conference on Atomic Physics (ICAP
Critical Point of an Interacting Two-Dimensional Atomic Bose Gas
We have measured the critical atom number in an array of harmonically trapped
two-dimensional (2D) Bose gases of rubidium atoms at different temperatures. We
found this number to be about five times higher than predicted by the
semi-classical theory of Bose-Einstein condensation (BEC) in the ideal gas.
This demonstrates that the conventional BEC picture is inapplicable in an
interacting 2D atomic gas, in sharp contrast to the three-dimensional case. A
simple heuristic model based on the Berezinskii-Kosterlitz-Thouless theory of
2D superfluidity and the local density approximation accounts well for our
experimental results
Measuring the Superfluid Fraction of an Ultracold Atomic Gas
We propose a method to measure the superfluid fraction of an atomic gas. The
method involves the use of a vector potential generated by optical beams with
non-zero angular momentum to simulate uniform rotation. The induced change in
angular momentum of the atomic gas can be measured spectroscopically. This
allows a direct determination of the superfluid fraction.Comment: 4 pages, 2 figure
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