449 research outputs found
Rotation induced superfluid-normal phase separation in trapped Fermi gases
We use the Bogoliubov-de Gennes formalism to analyze the effects of rotation
on the ground state phases of harmonically trapped Fermi gases, under the
assumption that quantized vortices are not excited. We find that the rotation
breaks Cooper pairs that are located near the trap edge, and that this leads to
a phase separation between the nonrotating superfluid (fully paired) atoms
located around the trap center and the rigidly rotating normal (nonpaired)
atoms located towards the trap edge, with a coexistence (partially paired)
region in between. Furthermore, we show that the superfluid phase that occurs
in the coexistence region is characterized by a gapless excitation spectrum,
and that it is distinct from the gapped phase that occurs near the trap center.Comment: 5 pages with 3 figure
Collapse and revival dynamics of superfluids of ultracold atoms in optical lattices
Recent experiments have shown a remarkable number of collapse-and-revival
oscillations of the matter-wave coherence of ultracold atoms in optical
lattices [Will et al., Nature 465, 197 (2010)]. Using a mean-field
approximation to the Bose-Hubbard model, we show that the visibility of
collapse-and-revival interference patterns reveal number squeezing of the
initial superfluid state. To describe the dynamics, we use an effective
Hamiltonian that incorporates the intrinsic two-body and induced three-body
interactions, and we analyze in detail the resulting complex pattern of
collapse-and-revival frequencies generated by virtual transitions to higher
bands, as a function of lattice parameters and mean-atom number. Our work shows
that a combined analysis of both the multiband, non-stationary dynamics in the
final deep lattice, and the number-squeezing of the initial superfluid state,
explains important characteristics of optical lattice collapse-and-revival
physics. Finally, by treating the two- and three-body interaction strengths,
and the coefficients describing the initial superposition of number states, as
free parameters in a fit to the experimental data it should be possible to go
beyond some of the limitations of our model and obtain insight into the
breakdown of the mean-field theory for the initial state or the role of
nonperturbative effects in the final state dynamics.Comment: 5 pages, 5 figures. This is the updated version published June 201
Rotational excitations in two-color photoassociation
We show that it is possible to excite higher rotational states J > 2 in
ultracold photoassociation by two laser fields. Usually higher J states are
suppressed in photoassociation at ultracold temperatures in the regime of
Wigner threshold laws. We propose a scheme in which one strong laser field
drives photoassociation transition close to either J = 1 or J = 2 rotational
state of a particular vibrational level of an electronically excited molecule.
The other laser field is tuned near photoassociation resonance with J > 2
rotational levels of the same vibrational state. The strong laser field induces
a strong continnum-bound dipole coupling. The resulting dipole force between
two colliding atoms modifies the continnum states forming continnum-bound
dressed states with a significant component of higher partial waves in the
continnum configuration. When the second laser is scanned near the resonance of
the higher J states, these states become populated due to photoassociative
transitions from the modified continnum.Comment: 8 Pages, 6 figure
Spontaneous dissociation of long-range Feshbach molecules
We study the spontaneous dissociation of diatomic molecules produced in cold atomic gases via magnetically tunable Feshbach resonances. We provide a universal formula for the lifetime of these molecules that relates their decay to the scattering length and the loss rate constant for inelastic spin relaxation. Our universal treatment as well as our exact coupled channels calculations for 85Rb dimers predict a suppression of the decay over several orders of magnitude when the scattering length is increased. Our predictions are in good agreement with recent measurements of the lifetime of 85Rb2
- …