209 research outputs found

    Condensed matter physics with trapped atomic Fermi gases

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    We present an overview of the various phase transitions that we anticipate to occur in trapped fermionic alkali gases. We also discuss the prospects of observing these transitions in (doubly) spin-polarized Li-6 and K-40 gases, which are now actively being studied by various experimental groups around the world.Comment: 18 pages of LaTeX and 2 postscript figures. Contribution to the international summer school `Enrico Fermi' on Bose-Einstein condensation in atomic gases, Varenna 199

    Theory of Interacting Quantum Gases

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    We present a unified picture of the interaction effects in dilute atomic quantum gases. We consider fermionic as well as bosonic gases and, in particular, discuss for both forms of statistics the fundamental differences between a gas with effectively repulsive and a gas with effectively attractive interatomic interactions, i.e.\ between a gas with either a positive or a negative scattering length.Comment: Invited paper for the NIST Journal of Researc

    Critical Temperature of a Trapped Bose Gas: Mean-Field Theory and Fluctuations

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    We investigate the possibilities of distinguishing the mean-field and fluctuation effects on the critical temperature of a trapped Bose gas with repulsive interatomic interactions. Since in a direct measurement of the critical temperature as a function of the number of trapped atoms these effects are small compared to the ideal gas results, we propose to observe Bose-Einstein condensation by adiabatically ramping down the trapping frequency. Moreover, analyzing this adiabatic cooling scheme, we show that fluctuation effects can lead to the formation of a Bose condensate at frequencies which are much larger than those predicted by the mean-field theory.Comment: 4 pages of ReVTeX and 3 figures. Submitted to Physical Review

    Cooper pair formation in trapped atomic Fermi gases

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    We apply the closed time-path formalism to evaluate the dynamics of the BCS transition to the superfluid state in trapped atomic 6^6Li. We find that the Fokker-Planck equation for the probability distribution of the order parameter is, sufficiently close to the critical temperature, identical to the equation that describes the switching on of a single-mode laser.Comment: 4 pages revtex including 1 figur

    Magnetic field control of elastic scattering in a cold gas of fermionic lithium atoms

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    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

    Critical temperature and Ginzburg-Landau equation for a trapped Fermi gas

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    We discuss a superfluid phase transition in a trapped neutral-atom Fermi gas. We consider the case where the critical temperature greatly exceeds the spacing between the trap levels and derive the corresponding Ginzburg-Landau equation. The latter turns out to be analogous to the equation for the condensate wave function in a trapped Bose gas. The analysis of its solution provides us with the value of the critical temperature TcT_{c} and with the spatial and temperature dependence of the order parameter in the vicinity of the phase transition point.Comment: 6 pages, 1 figure, REVTeX. The figure improved. Misprints corrected. More discussion adde

    The Superfluid State of Atomic Li6 in a Magnetic Trap

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    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.

    Effect of quantum group invariance on trapped Fermi gases

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    We study the properties of a thermodynamic system having the symmetry of a quantum group and interacting with a harmonic potential. We calculate the dependence of the chemical potential, heat capacity and spatial distribution of the gas on the quantum group parameter qq and the number of spatial dimensions DD. In addition, we consider a fourth-order interaction in the quantum group fields Ψ\Psi, and calculate the ground state energy up to first order.Comment: LaTeX file, 20 pages, four figures, uses epsf.sty, packaged as a single tar.gz uuencoded fil

    Inhibition of spontaneous emission in Fermi gases

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    Fermi inhibition is a quantum statistical analogue for the inhibition of spontaneous emission by an excited atom in a cavity. This is achieved when the relevant motional states are already occupied by a cloud of cold atoms in the internal ground state. We exhibit non-trivial effects at finite temperature and in anisotropic traps, and briefly consider a possible experimental realization.Comment: 4 pages with 3 figure

    Elastic and inelastic collisions of 6Li in magnetic and optical traps

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    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
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