156 research outputs found
Incompressible liquid state of rapidly-rotating bosons at filling factor 3/2
Bosons in the lowest Landau level, such as rapidly-rotating cold trapped
atoms, are investigated numerically in the specially interesting case in which
the filling factor (ratio of particle number to vortex number) is 3/2. When a
moderate amount of a longer-range (e.g. dipolar) interaction is included, we
find clear evidence that the ground state is in a phase constructed earlier by
two of us, in which excitations possess non-Abelian statistics.Comment: 5 pages, 5 figure
Observation of Vortex Pinning in Bose-Einstein Condensates
We report the observation of vortex pinning in rotating gaseous Bose-Einstein
condensates (BEC). The vortices are pinned to columnar pinning sites created by
a co-rotating optical lattice superimposed on the rotating BEC. We study the
effects of two different types of optical lattice, triangular and square. With
both geometries we see an orientation locking between the vortex and the
optical lattices. At sufficient intensity the square optical lattice induces a
structural cross-over in the vortex lattice.Comment: 4 pages, 6 figures. Replaced by final version to appear in Phys. Rev.
Let
Phases of a rotating Bose-Einstein condensate with anharmonic confinement
We examine an effectively repulsive Bose-Einstein condensate of atoms that
rotates in a quadratic-plus-quartic potential. With use of a variational method
we identify the three possible phases of the system (multiple quantization,
single quantization, and a mixed phase) as a function of the rotational
frequency of the gas and of the coupling constant. The derived phase diagram is
shown to be universal and the continuous transitions to be exact in the limit
of weak coupling and small anharmonicity. The variational results are found to
be consistent with numerical solutions of the Gross-Pitaevskii equation.Comment: 8 pages, 6 figure
Photonic band gap via quantum coherence in vortex lattices of Bose gases
We investigate the optical response of an atomic Bose-Einstein condensate
with a vortex lattice. We find that it is possible for the vortex lattice to
act as a photonic crystal and create photonic band gaps, by enhancing the
refractive index of the condensate via a quantum coherent scheme. If high
enough index contrast between the vortex core and the atomic sample is
achieved, a photonic band gap arises depending on the healing length and the
lattice spacing. A wide range of experimentally accessible parameters are
examined and band gaps in the visible region of the electromagnetic spectrum
are found. We also show how directional band gaps can be used to directly
measure the rotation frequency of the condensate.Comment: 4 pages, 4 figures, Final version to appear in PR
Nonequilibrium effects of anisotropic compression applied to vortex lattices in Bose-Einstein condensates
We have studied the dynamics of large vortex lattices in a dilute-gas
Bose-Einstein condensate. While undisturbed lattices have a regular hexagonal
structure, large-amplitude quadrupolar shape oscillations of the condensate are
shown to induce a wealth of nonequilibrium lattice dynamics. When exciting an m
= -2 mode, we observe shifting of lattice planes, changes of lattice structure,
and sheet-like structures in which individual vortices appear to have merged.
Excitation of an m = +2 mode dissolves the regular lattice, leading to randomly
arranged but still strictly parallel vortex lines.Comment: 5 pages, 6 figure
Solitons in coupled atomic-molecular Bose-Einstein condensates in a trap
We consider coupled atomic-molecular Bose-Einstein condensate system in a
quasi-one-dimensional trap. In the vicinity of a Feshbach resonance the system
can reveal soliton-like behavior. We analyze bright soliton solutions for the
system in the trap and in the presence of the interactions between particles.
We show that with increasing number of particles in the system two bright
soliton solutions start resembling dark soliton profiles known in an atomic
Bose-Einstein condensate with repulsive interactions between atoms. We analyze
also methods for experimental preparation and detection of the soliton states.Comment: 7 pages, 7 figures, published versio
Formation of Quantum-Degenerate Sodium Molecules
Ultra-cold sodium molecules were produced from an atomic Bose-Einstein
condensate by ramping an applied magnetic field across a Feshbach resonance.
More than molecules were generated with a conversion efficiency of
4%. Using laser light resonant with an atomic transition, the remaining
atoms could be selectively removed, preventing fast collisional relaxation of
the molecules. Time-of-flight analysis of the pure molecular sample yielded an
instantaneous phase-space density greater than 20.Comment: 5 pages, 4 figures (final published version
Dynamical role of anyonic excitation statistics in rapidly rotating Bose gases
We show that for rotating harmonically trapped Bose gases in a fractional
quantum Hall state, the anyonic excitation statistics in the rotating gas can
effectively play a {\em dynamical} role. For particular values of the
two-dimensional coupling constant , where is a
positive integer, the system becomes a noninteracting gas of anyons, with
exactly obtainable solutions satisfying Bogomol'nyi self-dual order parameter
equations. Attractive Bose gases under rapid rotation thus can be stabilized in
the thermodynamic limit due to the anyonic statistics of their quasiparticle
excitations.Comment: 4 pages of RevTex4; as published in Physical Review Letter
Coherent Molecular Optics using Sodium Dimers
Coherent molecular optics is performed using two-photon Bragg scattering.
Molecules were produced by sweeping an atomic Bose-Einstein condensate through
a Feshbach resonance. The spectral width of the molecular Bragg resonance
corresponded to an instantaneous temperature of 20 nK, indicating that atomic
coherence was transferred directly to the molecules. An autocorrelating
interference technique was used to observe the quadratic spatial dependence of
the phase of an expanding molecular cloud. Finally, atoms initially prepared in
two momentum states were observed to cross-pair with one another, forming
molecules in a third momentum state. This process is analogous to sum-frequency
generation in optics
The Experimental Observation of a Superfluid Gyroscope in a dilute Bose Condensed Gas
We have observed a superfluid gyroscope effect in a dilute gas Bose-Einstein
condensate. A condensate with a vortex possesses a single quantum of angular
momentum and this causes the plane of oscillation of the scissors mode to
precess around the vortex line. We have measured the precession rate of the
scissors oscillation. From this we deduced the angular momentum associated with
the vortex line and found a value close to per particle, as predicted
for a superfluid.Comment: 4 pages 5 fig
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