202 research outputs found
Dynamical evolution of a doubly-quantized vortex imprinted in a Bose-Einstein Condensate
The recent experiment by Y. Shin \emph{et al.} [Phys. Rev. Lett. \textbf{93},
160406 (2004)] on the decay of a doubly quantized vortex imprinted in Na condensates is analyzed by numerically solving the Gross-Pitaevskii
equation. Our results, which are in very good quantitative agreement with the
experiment, demonstrate that the vortex decay is mainly a consequence of
dynamical instability. Despite apparent contradictions, the local density
approach is consistent with the experimental results. The monotonic increase
observed in the vortex lifetimes is a consequence of the fact that, for large
condensates, the measured lifetimes incorporate the time it takes for the
initial perturbation to reach the central slice. When considered locally, the
splitting occurs approximately at the same time in every condensate, regardless
of its size.Comment: 5 pages, 4 figure
Vortex-Peierls States in Optical Lattices
We show that vortices, induced in cold atom superfluids in optical lattices,
may order in a novel vortex-Peierls ground state. In such a state vortices do
not form a simple lattice but arrange themselves in clusters, within which the
vortices are partially delocalized, tunneling between classically degenerate
configurations. We demonstrate that this exotic quantum many-body state is
selected by an order-from-disorder mechanism for a special combination of the
vortex filling and lattice geometry that has a macroscopic number of
classically degenerate ground states.Comment: 4 pages, 4 figures. Published versio
Giant vortices in combined harmonic and quartic traps
We consider a rotating Bose-Einstein condensate confined in combined harmonic
and quartic traps, following recent experiments [V. Bretin, S. Stock, Y. Seurin
and J. Dalibard, cond-mat/0307464]. We investigate numerically the behavior of
the wave function which solves the three-dimensional Gross Pitaevskii equation.
When the harmonic part of the potential is dominant, as the angular velocities
increases, the vortex lattice evolves into a giant vortex. We also
investigate a case not covered by the experiments or the previous numerical
works: for strong quartic potentials, the giant vortex is obtained for lower
, before the lattice is formed. We analyze in detail the three
dimensional structure of vortices
Phase Separation of a Fast Rotating Boson-Fermion Mixture in the Lowest-Landau-Level Regime
By minimizing the coupled mean-field energy functionals, we investigate the
ground-state properties of a rotating atomic boson-fermion mixture in a
two-dimensional parabolic trap. At high angular frequencies in the
mean-field-lowest-Landau-level regime, quantized vortices enter the bosonic
condensate, and a finite number of degenerate fermions form the
maximum-density-droplet state. As the boson-fermion coupling constant
increases, the maximum density droplet develops into a lower-density state
associated with the phase separation, revealing characteristics of a
Landau-level structure
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
Dissociation and Decay of Ultra-cold Sodium Molecules
The dissociation of ultracold molecules is studied by ramping an external
magnetic field through a Feshbach resonance. The observed dissociation energy
shows non-linear dependence on the ramp speed and directly yields the strength
of the atom-molecule coupling. In addition, inelastic molecule-molecule and
molecule-atom collisions are characterized
Energy gaps and roton structure above the nu=1/2 Laughlin state of a rotating dilute Bose-Einstein condensate
Exact diagonalization study of a rotating dilute Bose-Einstein condensate
reveals that as the first vortex enters the system the degeneracy of the
low-energy yrast spectrum is lifted and a large energy gap emerges. As more
vortices enter with faster rotation, the energy gap decreases towards zero, but
eventually the spectrum exhibits a rotonlike structure above the nu=1/2
Laughlin state without having a phonon branch despite the short-range nature of
the interaction.Comment: 4 pages, 4 figures, 1 tabl
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
Stirring Bose-Einstein condensate
By shining a tightly focused laser light on the condensate and moving the
center of the beam along the spiral line one may stir the condensate and create
vortices. It is shown that one can induce rotation of the condensate in the
direction opposite to the direction of the stirring.Comment: 4 pages, 5 figures, published versio
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
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