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 $^6$Li atoms into an ultracold gas of $^6$Li$_2$ molecules by adiabatic passage through a Feshbach resonance. Approximately $1.5 \times 10^5$ molecules in the least-bound, $v = 38$, vibrational level of the X$^1 \Sigma ^+_g$ 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 $T_{F}$, and (ii) increases the temperature to $T \geq T_{F}/4$ 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 $^6$Li Fermi mixture near a Feshbach resonance. The resonance is found at $800(40)$G in good agreement with theory. Anisotropic expansion of the gas is interpreted by collisional hydrodynamics. We observe an unexpected and large shift ($80$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 $^6$Li by direct evaporation in a CO$_2$ laser trap, yielding the first all-optically produced degenerate Fermi gas. More than $10^5$ atoms are confined at temperatures below $4 \mu$K at full trap depth, where the Fermi temperature for each state is $8 \mu$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