We report on the observation of a highly-degenerate, strongly-interacting Fermi gas of atoms. Fermionic 6 Li atoms in an optical trap are evaporatively cooled to degeneracy using a magnetic field to induce strong, resonant interactions. Upon abruptly releasing the cloud from the trap, the gas is observed to expand rapidly in the transverse direction while remaining nearly stationary in the axial. We interpret the expansion dynamics in terms of collisionless superfluid and collisional hydrodynamics. For the data taken at the longest evaporation times, we find that collisional hydrodynamics does not provide a satisfactory explanation, while superfluidity is plausible.As the fundamental constituents of matter are interacting fermions, the experimental study of stronglyinteracting, degenerate Fermi gases will impact theories in fields from particle physics to materials science. Although the interactions between fermions are understood when they are weak (e.g., quantum electrodynamics), the treatment of very strong interactions requires the development of new theoretical approaches. To test these new approaches, there is a need for experimental systems with widely tunable interaction strengths, densities, and temperatures. Ultracold atomic Fermi gases have exactly these properties, and thus enable tests of calculational techniques for fundamental systems ranging from quarks in nuclear matter to electrons in high temperature superconductors [1,2, 3,4,5,6,7,8,9,10,11]. For this reason, a number of groups are developing methods for creating and exploring ultracold atomic Fermi gases [12,13,14,15,16,17]. We report on the study of a strongly-interacting, degenerate Fermi gas. In contrast to the isotropic expansion previously observed for a noninteracting degenerate Fermi gas [12], we observe anisotropic expansion when the gas is released from an optical trap.An exciting feature of strongly-interacting atomic Fermi gases is the possibility of high-temperature superfluids that are analogs of very high temperature superconductors [8,9,10,11]. Our experiments produce the conditions predicted for this type of superfluid transition. Further, the anisotropic expansion we observe has been suggested as a signature of the onset of superfluidity in a Fermi gas [18]. We interpret the observed anisotropic expansion in terms of both collisionless superfluid hydrodynamics [18] and a new form of collisional hydrodynamics.Strong, magnetically-tunable interactions are achieved in our experiments by employing a Fermi gas comprising a 50-50 mixture of the two lowest hyperfine states of 6 Li, i.e., the |F = 1/2, M = ±1/2 states in the low-magnetic-field basis. This mixture has a predicted broad Feshbach resonance near an applied magnetic field of 860 G [19,20], where the energy of a bound 6 Li-6 Li molecular state is tuned into coincidence with the total energy of the colliding atoms. This enables the interaction strength to be widely varied [19,20,21,22]. It has also been suggested that interactions between fermions can be modified by immers...

We investigate the correlation properties of a one-dimensional interacting Bose gas by loading a magnetically trapped 87Rb Bose-Einstein condensate (BEC) into a deep two-dimensional optical lattice. We measure the three-body recombination rate for both the BEC in the magnetic trap and the BEC loaded into the optical lattice. The recombination rate coefficient is a factor of 7 smaller in the lattice, which we interpret as a reduction in the local three-body correlation function in the 1D case. This is a signature of correlation intermediate between that of the uncorrelated, phase coherent, 1D, mean-field regime and the strongly correlated Tonks-Girardeau regime.

We investigate the stability of a three spin state mixture of ultracold fermionic 6 Li atoms over a range of magnetic fields encompassing three Feshbach resonances. For most field values, we attribute decay of the atomic population to three-body processes involving one atom from each spin state and find that the three-body loss coefficient varies by over four orders of magnitude. We observe high stability when at least two of the three scattering lengths are small, rapid loss near the Feshbach resonances, and two unexpected resonant loss features. At our highest fields, where all pairwise scattering lengths are approaching at = −2140a0, we measure a three-body loss coefficient L3 ≃ 5 × 10 −22 cm 6 /s and a trend toward lower decay rates for higher fields indicating that future studies of color superfluidity and trion formation in a SU(3) symmetric Fermi gas may be feasible.

Using a simple model, we calculate the heating rates arising from laser intensity noise and beam-pointing fluctuations in far-off resonance optical traps. Intensity noise causes exponential heating, while beam-pointing noise causes heating at a constant rate. The achievement of heating time constants well beyond 10 sec imposes stringent requirements on the laser noise power spectra. Noise spectra are measured for a commercial argonion laser to illustrate the expected time scales.

We report the observation of strongly damped dipole oscillations of a quantum degenerate 1D atomic Bose gas in a combined harmonic and optical lattice potential. Damping is significant for very shallow axial lattices (0.25 photon recoil energies), and increases dramatically with increasing lattice depth, such that the gas becomes nearly immobile for times an order of magnitude longer than the single-particle tunneling time. Surprisingly, we see no broadening of the atomic quasimomentum distribution after damped motion. Recent theoretical work suggests that quantum fluctuations can strongly damp dipole oscillations of 1D atomic Bose gas, providing a possible explanation for our observations.PACS numbers: 03.75. Kk, 05.60.Gg, 73.43.Nq The ability of highly degenerate quantum systems to sustain dissipationless flow is one of the most striking manifestations of quantum mechanics. However, transport in such systems can be dramatically modified by the presence of a relatively weak, but rapidly spatially varying ("corrugated") potential along the transport axis. For example, the periodic potential of an optical lattice inhibits transport in a degenerate Fermi atomic gas [1, 2, 3], but not, in general, in a degenerate Bose gas (i.e., Bose-Einstein Condensate (BEC)) [4,5]. However, under certain conditions, highly dissipative transport in a BEC in an optical lattice [6,7,8] can arise from nonlinear dynamical instabilities [9,10,11]. In low dimensional systems, of which 1D atomic gases [12,13,14,15,16] and superconducting nanowires [17] are important experimentally realized examples, a corrugated potential can cause dramatic changes in ground state and transport properties.We study inhibited transport in a 1D Bose gas in the presence of an optical lattice along the 1D axis. In the absence of such a lattice, dipole oscillations are undamped [14], since it is a general result that the dipole mode of a harmonically confined gas is unaffected by 2-body interactions (generalized Kohn's theorem) [18]. This result does not strictly hold for a combined harmonic and periodic potential; nevertheless, undamped oscillations have been observed in 3D BECs for small amplitudes and weak interactions [5,19].In this Letter we report a study of strongly damped dipole oscillations of a 1D Bose gas in a combined harmonic and periodic potential, under conditions for which undamped motion has been observed previously for 3D BECs. This striking difference between 1D and 3D was recently reported, qualitatively, in Ref. [13]. Here we measure the damped motion as a function of axial lattice depth. Significant damping is induced by very shallow lattices, and in deeper lattices the motion is overdamped to the degree that the gas is nearly immobile for times an order of magnitude longer than the single-particle tunneling time. We emphasize, and discuss further below, that the inhibited transport is not due to Bloch oscillations [4,20], where transport is frustrated by Bragg reflection at the Brillouin zone (BZ) boundary, as has been seen in previou...

We achieve degeneracy in a mixture of the two lowest hyperfine states of 6Li by direct evaporation in a CO2 laser trap, yielding the first all optically produced degenerate Fermi gas. More than 10(5) atoms are confined at temperatures below 4 microK at full trap depth, where the Fermi temperature for each state is 8 microK. This degenerate two-component mixture is ideal for exploring mechanisms of superconductivity ranging from Cooper pairing to Bose-Einstein condensation of strongly bound pairs.

We observe enhanced three-body recombination in a three-component ;{6}Li Fermi gas attributable to an excited Efimov trimer state intersecting the three-atom scattering threshold near 895 G. From measurements of the recombination rate we determine the Efimov parameters kappa_{*} and eta_{*} for the universal region above 600 G which includes three overlapping Feshbach resonances. The value of kappa_{*} also predicts the locations of loss features previously observed near 130 and 500 G [T. B. Ottenstein, Phys. Rev. Lett. 101, 203202 (2008)10.1103/PhysRevLett.101.203202; J. H. Huckans, Phys. Rev. Lett. 102, 165302 (2009)10.1103/PhysRevLett.102.165302] suggesting they are associated with a ground-state Efimov trimer near threshold. We also report on the realization of a degenerate three-component Fermi gas with approximate SU(3) symmetry.

A Fokker-Planck equation is derived for the energy distribution of atoms in a three-dimensional harmonic trap with fluctuations in the spring constant and the equilibrium position. Using this model, we predict trap lifetimes based on the measurable noise spectra of the fluctuations. The energy distributions evolve into a single eigenmode where the apparent temperature of the distribution remains constant while the population decays as a consequence of the energy input. The method of analysis and the corresponding results are applicable to any optical, magnetic, or ion trap that is approximately harmonic, and offer useful insights into both noise-induced and optical heating processes. ͓S1050-2947͑98͒05211-1͔