997 research outputs found
Radiative collisional heating at the Doppler limit for laser-cooled magnesium atoms
We report Monte Carlo wave function simulation results on cold collisions
between magnesium atoms in a strong red-detuned laser field. This is the normal
situation e.g. in magneto-optical traps (MOT). The Doppler limit heating rate
due to radiative collisions is calculated for Mg-24 atoms in a magneto-optical
trap based on the singlet S_0 - singlet P_1 atomic laser cooling transition. We
find that radiative heating does not seem to affect the Doppler limit in this
case. We also describe a channelling mechanism due to the missing Q branch in
the excitation scheme, which could lead to a suppression of inelastic
collisions, and find that this mechanism is not present in our simulation
results due to the multistate character of the excitation process.Comment: 4 pages, RevTeX 4; v2 contains minor revisions based on referee
comments (5 pages
Construction of a giant vortex state in a trapped Fermi system
A superfluid atomic Fermi system may support a giant vortex if the trapping
potential is anharmonic. In such a potential, the single-particle spectrum has
a positive curvature as a function of angular momentum. A tractable model is
put up in which the lowest and next lowest Landau levels are occupied.
Different parameter regimes are identified and characterized. Due to the
dependence of the interaction on angular momentum quantum number, the Cooper
pairing is at its strongest not only close to the Fermi level, but also close
to the energy minimum. It is shown that the gas is superfluid in the interior
of the toroidal density distribution and normal in the outer regions.
Furthermore, the pairing may give rise to a localized density depression in
configuration space.Comment: 12 pages, 14 figure file
Stability of the solutions of the Gross-Pitaevskii equation
We examine the static and dynamic stability of the solutions of the
Gross-Pitaevskii equation and demonstrate the intimate connection between them.
All salient features related to dynamic stability are reflected systematically
in static properties. We find, for example, the obvious result that static
stability always implies dynamic stability and present a simple explanation of
the fact that dynamic stability can exist even in the presence of static
instability.Comment: 7 pages, 1 figur
Dipole and monopole modes in the Bose-Hubbard model in a trap
The lowest-lying collective modes of a trapped Bose gas in an optical lattice
are studied in the Bose-Hubbard model. An exact diagonalization of the
Hamiltonian is performed in a one-dimensional five-particle system in order to
find the lowest few eigenstates. Dipole and breathing character of the
eigenstates is confirmed in the limit where the tunneling dominates the
dynamics, but under Mott-like conditions the excitations do not correspond to
oscillatory modes.Comment: 19 pages, 11 figures; submitted to Phys. Rev.
Dynamical stability of a doubly quantized vortex in a three-dimensional condensate
The Bogoliubov equations are solved for a three-dimensional Bose-Einstein
condensate containing a doubly quantized vortex, trapped in a harmonic
potential. Complex frequencies, signifying dynamical instability, are found for
certain ranges of parameter values. The existence of alternating windows of
stability and instability, respectively, is explained qualitatively and
quantitatively using variational calculus and direct numerical solution. It is
seen that the windows of stability are much smaller for a cigar shaped
condensate than for a pancake shaped one, which is consistent with the findings
of recent experiments.Comment: 23 pages, 11 figure
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