51 research outputs found
Condensed matter physics with trapped atomic Fermi gases
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
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
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
We apply the closed time-path formalism to evaluate the dynamics of the BCS
transition to the superfluid state in trapped atomic Li. 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
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
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.
Explosion of a collapsing Bose-Einstein condensate
We show that elastic collisions between atoms in a Bose-Einstein condensate
with attractive interactions lead to an explosion that ejects a large fraction
of the collapsing condensate. We study variationally the dynamics of this
explosion and find excellent agreement with recent experiments on magnetically
trapped Rubidium-85. We also determine the energy and angular distribution of
the ejected atoms during the collapse.Comment: Four pages of ReVTeX and five postscript figure
Superfluidity of spin-polarized 6Li
We study the prospects for observing superfluidity in a spin-polarized atomic
gas of Li atoms, using state-of-the-art interatomic potentials. We
determine the spinodal line and show that a BCS transition to the superfluid
state can indeed occur in the (meta)stable region of the phase diagram if the
densities are sufficiently low. Moreover, for a total density of
, which still fulfills this requirement, we find a critical
temperature of only . We also discuss the stability of the gas due to
exchange and dipolar relaxation and conclude that the prospects for observing
superfluidity in a magnetically trapped atomic Li gas are particularly
promising for magnetic bias fields larger than .Comment: 4 pages of ReVTeX and 2 uuencoded figures. Submitted for publication
in Physical Review Letter
Stability of Bose condensed atomic Li-7
We study the stability of a Bose condensate of atomic Li in a (harmonic
oscillator) magnetic trap at non-zero temperatures. In analogy to the stability
criterion for a neutron star, we conjecture that the gas becomes unstable if
the free energy as a function of the central density of the cloud has a local
extremum which conserves the number of particles. Moreover, we show that the
number of condensate particles at the point of instability decreases with
increasing temperature, and that for the temperature interval considered, the
normal part of the gas is stable against density fluctuations at this point.Comment: Submitted for publication in Physical Review
Critical temperature and Ginzburg-Landau equation for a trapped Fermi gas
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 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
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