387 research outputs found
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
Optical tuning of the scattering length of cold alkaline earth atoms
It is possible to tune the scattering length for the collision of ultra-cold
1S0 ground state alkaline-earth atoms using an optical Feshbach resonance. This
is achieved with a laser far detuned from an excited molecular level near the
frequency of the atomic intercombination 1S0--3P1 transition. Simple resonant
scattering theory, illustrated by the example of 40Ca, allows an estimate of
the magnitude of the effect. Unlike alkali metal species, large changes of the
scattering length are possible while atom loss remains small, because of the
very narrow line width of the molecular photoassociation transition. This
raises prospects for control of atomic interactions for a system without
magnetically tunable Feshbach resonance levels
Photoassociation spectroscopy of cold alkaline earth atoms near the intercombination line
The properties of photoassociation (PA) spectra near the intercombination
line (the weak transition between and states) of group
II atoms are theoretically investigated. As an example we have carried out a
calculation for Calcium atoms colliding at ultra low temperatures of 1 mK, 1
K, and 1 nK. Unlike in most current photoassociation spectroscopy the
Doppler effect can significantly affect the shape of the investigated lines.
Spectra are obtained using Ca--Ca and Ca--Ca short-range {\it ab initio}
potentials and long-range van der Waals and resonance dipole potentials. The
similar van der Waals coefficients of ground and
excited states cause the PA to differ greatly from
those of strong, allowed transitions with resonant dipole interactions. The
density of spectral lines is lower, the Condon points are at relatively short
range, and the reflection approximation for the Franck-Condon factors is not
applicable, and the spontaneous decay to bound ground-state molecules is
efficient. Finally, the possibility of efficient production of cold molecules
is discussed
- …