141 research outputs found
The Superfluid State of Atomic Li6 in a Magnetic Trap
We report on a study of the superfluid state of spin-polarized atomic Li6
confined in a magnetic trap. Density profiles of this degenerate Fermi gas, and
the spatial distribution of the BCS order parameter are calculated in the local
density approximation. The critical temperature is determined as a function of
the number of particles in the trap. Furthermore we consider the mechanical
stability of an interacting two-component Fermi gas, both in the case of
attractive and repulsive interatomic interactions. For spin-polarized Li6 we
also calculate the decay rate of the gas, and show that within the mechanically
stable regime of phase space, the lifetime is long enough to perform
experiments on the gas below and above the critical temperature if a bias
magnetic field of about 5 T is applied. Moreover, we propose that a measurement
of the decay rate of the system might signal the presence of the superfluid
state.Comment: 16 pages Revtex including 10 figures, submitted to Phys. Rev.
Magnetic field control of elastic scattering in a cold gas of fermionic lithium atoms
We study elastic collisions in an optically trapped spin mixture of fermionic
lithium atoms in the presence of magnetic fields up to 1.5kG by measuring
evaporative loss. Our experiments confirm the expected magnetic tunability of
the scattering length by showing the main features of elastic scattering
according to recent calculations. We measure the zero crossing of the
scattering length that is associated with a predicted Feshbach resonance at
530(3)G. Beyond the resonance we observe the expected large cross section in
the triplet scattering regime
Elastic and inelastic collisions of 6Li in magnetic and optical traps
We use a full coupled channels method to calculate collisional properties of
magnetically or optically trapped ultracold 6Li. The magnetic field dependence
of the s-wave scattering lengths of several mixtures of hyperfine states are
determined, as are the decay rates due to exchange collisions. In one case, we
find Feshbach resonances at B=0.08 T and B=1.98 T. We show that the exact
coupled channels calculation is well approximated over the entire range of
magnetic fields by a simple analytical calculation.Comment: 4 pages revtex including 4 figures, submitted to PR
Conversion of an Atomic Fermi Gas to a Long-Lived Molecular Bose Gas
We have converted an ultracold Fermi gas of Li atoms into an ultracold
gas of Li molecules by adiabatic passage through a Feshbach resonance.
Approximately molecules in the least-bound, ,
vibrational level of the X singlet state are produced with an
efficiency of 50%. The molecules remain confined in an optical trap for times
of up to 1 s before we dissociate them by a reverse adiabatic sweep.Comment: Accepted for publication in Phys. Rev. Letter
Two-species mixture of quantum degenerate Bose and Fermi gases
We have produced a macroscopic quantum system in which a Li-6 Fermi sea
coexists with a large and stable Na-23 Bose-Einstein condensate. This was
accomplished using inter-species sympathetic cooling of fermionic Li-6 in a
thermal bath of bosonic Na-23
Degenerate fermion gas heating by hole creation
Loss processes that remove particles from an atom trap leave holes behind in
the single particle distribution if the trapped gas is a degenerate fermion
system. The appearance of holes increases the temperature and we show that the
heating is (i) significant if the initial temperature is well below the Fermi
temperature , and (ii) increases the temperature to
after half of the system's lifetime, regardless of the initial temperature. The
hole heating has important consequences for the prospect of observing
Cooper-pairing in atom traps.Comment: to be published in PR
Measurement of interaction energy near a Feshbach resonance in a 6Li Fermi gas
We investigate the strongly interacting regime in an optically trapped Li
Fermi mixture near a Feshbach resonance. The resonance is found at G
in good agreement with theory. Anisotropic expansion of the gas is interpreted
by collisional hydrodynamics. We observe an unexpected and large shift (G)
between the resonance peak and both the maximum of atom loss and the change of
sign of the interaction energy.Comment: 4 pages, 4 figure
Sympathetic cooling of an atomic Bose-Fermi gas mixture
Sympathetic cooling of an atomic Fermi gas by a Bose gas is studied by
solution of the coupled quantum Boltzmann equations for the confined gas
mixture. Results for equilibrium temperatures and relaxation dynamics are
presented, and some simple models developed. Our study illustrate that a
combination of sympathetic and forced evaporative cooling enables the Fermi gas
to be cooled to the degenerate regime where quantum statistics, and mean field
effects are important. The influence of mean field effects on the equilibrium
spatial distributions is discussed qualitatively.Comment: 8 pages, 9 figures, accepted for publication in Phys.Rev.Let
All-Optical Production of a Degenerate Fermi Gas
We achieve degeneracy in a mixture of the two lowest hyperfine states of
Li by direct evaporation in a CO laser trap, yielding the first
all-optically produced degenerate Fermi gas. More than atoms are
confined at temperatures below K at full trap depth, where the Fermi
temperature for each state is K. This degenerate two-component mixture
is ideal for exploring mechanisms of superconductivity ranging from Cooper
pairing to Bose condensation of strongly bound pairs.Comment: 4 pgs RevTeX with 2 eps figs, to be published in Phys. Rev. Let
Analytical treatment of interacting Fermi gas in arbitrary dimensional harmonic trap
We study normal state properties of an interacting Fermi gas in an isotropic
harmonic trap of arbitrary dimensions. We exactly calculate the first-order
perturbation terms in the ground state energy and chemical potential, and
obtain simple analytic expressions of the total energy and chemical potential.
At zero temperature, we find that Thomas-Fermi approximation agrees well with
exact results for any dimension even though system is dilute and small, i.e.
when the Thomas-Fermi approximation is generally expected to fail. In the high
temperature (classical) region, we find interaction energy decreases in
proportion to T^(-d/2), where T is temperature and d is dimension of the
system. Effect of interaction in the ground state in two and three-dimensional
systems is also discussed.Comment: 15 pages, 4 figure
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