2,820 research outputs found
A Simple Quantum Model of Ultracold Polar Molecule Collisions
We present a unified formalism for describing chemical reaction rates of
trapped, ultracold molecules. This formalism reduces the scattering to its
essential features, namely, a propagation of the reactant molecules through a
gauntlet of long-range forces before they ultimately encounter one another,
followed by a probability for the reaction to occur once they do. In this way,
the electric-field dependence should be readily parametrized in terms of a pair
of fitting parameters (along with a coefficient) for each asymptotic
value of partial wave quantum numbers . From this, the electric
field dependence of the collision rates follows automatically. We present
examples for reactive species such as KRb, and non-reactive species, such as
RbCs
p-wave Feshbach molecules
We have produced and detected molecules using a p-wave Feshbach resonance
between 40K atoms. We have measured the binding energy and lifetime for these
molecules and we find that the binding energy scales approximately linearly
with magnetic field near the resonance. The lifetime of bound p-wave molecules
is measured to be 1.0 +/- 0.1 ms and 2.3 +/- 0.2 ms for the m_l = +/- 1 and m_l
= 0 angular momentum projections, respectively. At magnetic fields above the
resonance, we detect quasi-bound molecules whose lifetime is set by the
tunneling rate through the centrifugal barrier
Pair Wave Functions in Atomic Fermi Condensates
Recent experiments have observed condensation behavior in a strongly
interacting system of fermionic atoms. We interpret these observations in terms
of a mean-field version of resonance superfluidity theory. We find that the
objects condensed are not bosonic molecules composed of bound fermion pairs,
but are rather spatially correlated Cooper pairs whose coherence length is
comparable to the mean spacing between atoms. We propose experiments that will
help to further probe these novel pairs
Dipolar Bose gases: Many-body versus mean-field description
We characterize zero-temperature dipolar Bose gases under external spherical
confinement as a function of the dipole strength using the essentially exact
many-body diffusion Monte Carlo (DMC) technique. We show that the DMC energies
are reproduced accurately within a mean-field framework if the variation of the
s-wave scattering length with the dipole strength is accounted for properly.
Our calculations suggest stability diagrams and collapse mechanisms of dipolar
Bose gases that differ significantly from those previously proposed in the
literature
Quench-produced solitons in a box-trapped Bose-Einstein condensate
We describe a protocol to prepare solitons in a quasi-1d box-trapped
Bose-Einstein condensate using only a quench of the isotropic s-wave scattering
length. A quench to exactly four times the initial 1d coupling strength creates
one soliton at each boundary of the box, which then propagate in a uniform
background density and collide with one another. No nonsolotonic excitations
are created during the quench. The procedure is robust against imperfections in
the scattering length ramp rate and a mismatch of the final scattering length
Observation of Heteronuclear Feshbach Resonances in a Bose-Fermi Mixture
Three magnetic-field induced heteronuclear Feshbach resonances were
identified in collisions between bosonic 87Rb and fermionic 40K atoms in their
absolute ground states. Strong inelastic loss from an optically trapped mixture
was observed at the resonance positions of 492, 512, and 543 +/- 2 G. The
magnetic-field locations of these resonances place a tight constraint on the
triplet and singlet cross-species scattering lengths, yielding -281 +/- 15 Bohr
and -54 +/- 12 Bohr, respectively. The width of the loss feature at 543 G is
3.7 +/- 1.5 G wide; this broad Feshbach resonance should enable experimental
control of the interspecies interactions.Comment: revtex4 + 5 EPS figure
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