150 research outputs found
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
Bose-Einstein Condensates in Rotating Lattices
Strongly interacting bosons in 2D in a rotating square lattice are
investigated via a modified Bose-Hubbard Hamiltonian. Such a system corresponds
to a rotating lattice potential imprinted on a trapped Bose-Einstein
condensate. Second-order quantum phase transitions between states of different
symmetries are observed at discrete rotation rates. For the square lattice we
study, there are four possible ground-state symmetries.Comment: 4 pages, 5 figures, Accepted for publication in PRL v2: Replaced
phase winding labels with symmetry eigenstate indices, replaced Gaussian
Ansatz with more general treatment and other minor change
Nonlinear Transport of Bose-Einstein Condensates Through Waveguides with Disorder
We study the coherent flow of a guided Bose-Einstein condensate incident over
a disordered region of length L. We introduce a model of disordered potential
that originates from magnetic fluctuations inherent to microfabricated guides.
This model allows for analytical and numerical studies of realistic transport
experiments. The repulsive interaction among the condensate atoms in the beam
induces different transport regimes. Below some critical interaction (or for
sufficiently small L) a stationary flow is observed. In this regime, the
transmission decreases exponentially with L. For strong interaction (or large
L), the system displays a transition towards a time dependent flow with an
algebraic decay of the time averaged transmission.Comment: 15 pages, 9 figure
Vortex phase diagram in rotating two-component Bose-Einstein condensates
We investigate the structure of vortex states in rotating two-component
Bose-Einstein condensates with equal intracomponent but varying intercomponent
coupling constants. A phase diagram in the intercomponent-coupling versus
rotation-frequency plane reveals rich equilibrium structures of vortex states.
As the ratio of intercomponent to intracomponent couplings increases, the
interlocked vortex lattices undergo phase transitions from triangular to
square, to double-core lattices, and eventually develop interwoven "serpentine"
vortex sheets with each component made up of chains of singly quantized
vortices.Comment: 4 pages, 4 figures, revtex
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
Response of an atomic Bose-Einstein condensate to a rotating elliptical trap
We investigate numerically the response of an atomic Bose-Einstein condensate
to a weakly-elliptical rotating trap over a large range of rotation
frequencies. We analyse the quadrupolar shape oscillation excited by rotation,
and discriminate between its stable and unstable regimes. In the latter case,
where a vortex lattice forms, we compare with experimental observations and
find good agreement. By examining the role of thermal atoms in the process, we
infer that the process is temperature-independent, and show how terminating the
rotation gives control over the number of vortices in the lattice. We also
study the case of critical rotation at the trap frequency, and observe large
centre-of-mass oscillations of the condensate.Comment: 14 pages, 8 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
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
Sodium Bose-Einstein Condensates in an Optical Lattice
The phase transition from a superfluid to a Mott insulator has been observed
in a Na Bose-Einstein condensate. A dye laser detuned nm red
of the Na SP transition was used to form the three
dimensional optical lattice. The heating effects of the small detuning as well
as the three-body decay processes constrained the timescale of the experiment.
Certain lattice detunings were found to induce a large loss of atoms. These
loss features were shown to be due to photoassociation of atoms to vibrational
levels in the Na state.Comment: Figures somewhat compromised due to size reductio
Spin textures in slowly rotating Bose-Einstein Condensates
Slowly rotating spin-1 Bose-Einstein condensates are studied through a
variational approach based upon lowest Landau level calculus. The author finds
that in a gas with ferromagnetic interactions, such as Rb, angular
momentum is predominantly carried by clusters of two different types of
skyrmion textures in the spin-vector order parameter. Conversely, in a gas with
antiferromagnetic interactions, such as Na, angular momentum is carried
by -disclinations in the nematic order parameter which arises from spin
fluctuations. For experimentally relevant parameters, the cores of these
-disclinations are ferromagnetic, and can be imaged with polarized light.Comment: 14 pages, 12 low resolution bitmapped figures, RevTeX4. High
resolution figures available from author. Suplementary movies available from
autho
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