104 research outputs found
Feshbach resonances in ultracold gases
In this chapter, we describe scattering resonance phenomena in general, and
focus on the mechanism of Feshbach resonances, for which a multi-channel
treatment is required. We derive the dependence of the scattering phase shift
on magnetic field and collision energy. From this, the scattering length and
effective range coefficient can be extracted, expressions which are
particularly useful for ultracold gases.Comment: 23 pages, 3 figures. This article will be published as Chapter 4 in
"Quantum gas experiments - exploring many-body states", edited by P.
T\"orm\"a and K. Sengstock, Imperial College Press, London, to be published
201
Ramsey fringes in a Bose-Einstein condensate between atoms and molecules
In a recent experiment, a Feshbach scattering resonance was exploited to
observe Ramsey fringes in a Rb Bose-Einstein condensate. The oscillation
frequency corresponded to the binding energy of the molecular state. We show
that the observations are remarkably consistent with predictions of a resonance
field theory in which the fringes arise from oscillations between atoms and
molecules.Comment: 5 pages, 5 figure
BCS-BEC crossover in a strongly correlated Fermi gas
We study the BCS-BEC crossover in the strongly correlated regime of an
ultra-cold rotating two component Fermi gas. Strong correlations are shown to
generate an additional long-range interaction which results in a modified
crossover region compared to the non-rotating situation. The two-particle
correlation function reveals a smooth crossover between the s-wave paired
fermionic fractional quantum Hall state and the bosonic Laughlin state.Comment: 4 pages, 3 figure
Feshbach resonances and collapsing Bose-Einstein condensates
We investigate the quantum state of burst atoms seen in the recent Rb-85
experiments at JILA. We show that the presence of a resonance scattering state
can lead to a pairing instability generating an outflow of atoms with energy
comparable to that observed. A resonance effective field theory is used to
study this dynamical process in an inhomogeneous system with spherical
symmetry
Feshbach resonances with large background scattering length: interplay with open-channel resonances
Feshbach resonances are commonly described by a single-resonance Feshbach
model, and open-channel resonances are not taken into account explicitly.
However, an open-channel resonance near threshold limits the range of validity
of this model. Such a situation exists when the background scattering length is
much larger than the range of the interatomic potential. The open-channel
resonance introduces strong threshold effects not included in the
single-resonance description. We derive an easy-to-use analytical model that
takes into account both the Feshbach resonance and the open-channel resonance.
We apply our model to Rb, which has a large background scattering
length, and show that the agreement with coupled-channels calculations is
excellent. The model can be readily applied to other atomic systems with a
large background scattering length, such as Li and Cs. Our approach
provides full insight into the underlying physics of the interplay between
open-channel (or potential) resonances and Feshbach resonances.Comment: 16 pages, 12 figures, accepted for publication in Phys. Rev. A; v2:
added reference
Scattering hypervolume for ultracold bosons from weak to strong interactions
The elastic scattering properties of three bosons at low energy enter the
many-body description of ultracold Bose gases via the three-body scattering
hypervolume . We study this quantity for identical bosons that interact via
a pairwise finite-range potential. Our calculations cover the regime from
strongly repulsive potentials towards attractive potentials supporting multiple
two-body bound states and are consistent with the few existing predictions for
. We present the first numerical confirmation of the universal predictions
for in the strongly interacting regime, where Efimov physics dominates, for
a local nonzero-range potential. Our findings highlight how is influenced
by three-body quasibound states with strong -wave or -wave
characteristics in the weakly interacting regime.Comment: 13 pages, 8 figure
Production of Long-Lived Ultracold Li2 Molecules from a Fermi gas
We create weakly-bound Li2 molecules from a degenerate two component Fermi
gas by sweeping a magnetic field across a Feshbach resonance. The atom-molecule
transfer efficiency can reach 85% and is studied as a function of magnetic
field and initial temperature. The bosonic molecules remain trapped for 0.5 s
and their temperature is within a factor of 2 from the Bose-Einstein
condensation temperature. A thermodynamical model reproduces qualitatively the
experimental findings
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