357 research outputs found
Asymptotic Bound-state Model for Feshbach Resonances
We present an Asymptotic Bound-state Model which can be used to accurately
describe all Feshbach resonance positions and widths in a two-body system. With
this model we determine the coupled bound states of a particular two-body
system. The model is based on analytic properties of the two-body Hamiltonian,
and on asymptotic properties of uncoupled bound states in the interaction
potentials. In its most simple version, the only necessary parameters are the
least bound state energies and actual potentials are not used. The complexity
of the model can be stepwise increased by introducing threshold effects,
multiple vibrational levels and additional potential parameters. The model is
extensively tested on the 6Li-40K system and additional calculations on the
40K-87Rb system are presented.Comment: 13 pages, 8 figure
Broad Feshbach resonance in the 6Li-40K mixture
We study the widths of interspecies Feshbach resonances in a mixture of the
fermionic quantum gases 6Li and 40K. We develop a model to calculate the width
and position of all available Feshbach resonances for a system. Using the model
we select the optimal resonance to study the 6Li/40K mixture. Experimentally,
we obtain the asymmetric Fano lineshape of the interspecies elastic cross
section by measuring the distillation rate of 6Li atoms from a potassium-rich
6Li/40K mixture as a function of magnetic field. This provides us with the
first experimental determination of the width of a resonance in this mixture,
Delta B=1.5(5) G. Our results offer good perspectives for the observation of
universal crossover physics using this mass-imbalanced fermionic mixture.Comment: 4 pages, 2 figure
Adiabatically changing the phase-space density of a trapped Bose gas
We show that the degeneracy parameter of a trapped Bose gas can be changed
adiabatically in a reversible way, both in the Boltzmann regime and in the
degenerate Bose regime. We have performed measurements on spin-polarized atomic
hydrogen in the Boltzmann regime demonstrating reversible changes of the
degeneracy parameter (phase-space density) by more than a factor of two. This
result is in perfect agreement with theory. By extending our theoretical
analysis to the quantum degenerate regime we predict that, starting close
enough to the Bose-Einstein phase transition, one can cross the transition by
an adiabatic change of the trap shape.Comment: 4 pages, 3 figures, Latex, submitted to PR
Exploring an ultracold Fermi-Fermi mixture: Interspecies Feshbach resonances and scattering properties of 6Li and 40K
We report on the observation of Feshbach resonances in an ultracold mixture
of two fermionic species, 6Li and 40K. The experimental data are interpreted
using a simple asymptotic bound state model and full coupled channels
calculations. This unambiguously assigns the observed resonances in terms of
various s- and p-wave molecular states and fully characterizes the ground-state
scattering properties in any combination of spin states.Comment: 4 pages, 4 figures, 1 tabl
Direct Microscopic Study of Doubly Polarized Atomic Hydrogen by Electron-Spin Resonance
By means of ESR in a high magnetic field the hyperfine states of a gas of spin-polarized atomic hydrogen are directly probed. This allows a direct determination of the spin-state populations and nuclear polarization. The unusual ESR line shape is attributed to field inhomogeneities. The temperature of the gas was determined by use of ESR with no indication of nonequilibrium due to Kapitza resistance. Recombination rates between hyperfine states could be determined
Damping of low-energy excitations of a trapped Bose condensate at finite temperatures
We present the theory of damping of low-energy excitations of a trapped Bose
condensate at finite temperatures, where the damping is provided by the
interaction of these excitations with the thermal excitations. We emphasize the
key role of stochastization in the behavior of the thermal excitations for
damping in non-spherical traps. The damping rates of the lowest excitations,
following from our theory, are in fair agreement with the data of recent JILA
and MIT experiments. The damping of quasiclassical excitations is determined by
the condensate boundary region, and the result for the damping rate is
drastically different from that in a spatially homogeneous gas.Comment: 10 pages RevTeX, correction of the misprints and addition of the
sentence clarifying the result for quasiclassical excitationscorrection of
the misprints and addition of the sentence clarifying the result for
quasiclassical excitation
Regimes of quantum degeneracy in trapped 1D gases
We discuss the regimes of quantum degeneracy in a trapped 1D gas and obtain
the diagram of states. Three regimes have been identified: the BEC regimes of a
true condensate and quasicondensate, and the regime of a trapped gas of Tonks
(gas of impenetrable bosons). The presence of a sharp cross-over to the BEC
regime requires extremely small interaction between particles. We discuss how
to distinguish between true and quasicondensates in phase coherence
experiments.Comment: 4 pages, 1 eps figur
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