Trapped Atomic Fermi Gas

Sierk Pötting

Tara E. Drake, Yoav Sagi, Rabin Paudel +3 more

The ideal (i.e., noninteracting), homogeneous Fermi gas, with its characteristic sharp Fermi surface in the momentum distribution, is a fundamental concept relevant to the behavior of many systems. With trapped Fermi gases of ultracold atoms, one can realize and probe a nearly ideal Fermi gas; however, these systems have a nonuniform density due to the confining potential. We show that the effect of the density variation, which typically washes out any semblance of a Fermi surface step in the momentum distribution, can be mitigated by selectively probing atoms near the center of a trapped gas. With this approach, we have directly measured a Fermi surface in momentum space for a nearly ideal gas, where the average density and temperature of the probed portion of the gas can be determined from the location and sharpness of the Fermi surface.

M.Ya. Amusia, A.Z. Msezane, Vasily R. Shaginyan

Vyacheslav Afanasievich Vinogradov, K. A. Karpov, Sergey S. Lukashov +2 more

Abstract In this paper, we discuss the search for the Fulde–Ferrell–Larkin–Ovchinnikov superfluid phase in an ultracold gas of Fermi atoms. A possible obstacle to obtaining this phase in known experiments is, first of all, the separation of the gas into a spin-balanced phase and a completely polarized phase. This phase separation is caused by confinement in an external parabolic potential. A second possible obstacle is the insufficiently low temperature-to-Fermi energy ratio. Trapping the gas in a large-scale optical-dipole trap with a flat potential inside will avoid phase separation. Moreover, the trap will allow an increase in the number of atoms, which, in turn, can lead to a decrease in the temperature relative to the Fermi energy. The results of a primary experiment on loading atoms into a similar trap from a magneto-optical trap are presented.

Georg M. Bruun

We examine a dilute two-component atomic Fermi gas trapped in a harmonic potential in the superfluid phase. For experimentally realistic parameters, the trapping potential is shown to have crucial influence on various properties of the gas. Using an effective Hamiltonian, analytical results for the critical temperature, the temperature dependence of the superfluid gap, and the energy of the lowest collective modes are derived. These results are shown to agree well with numerical calculations. We also discuss in more detail a previously proposed method to experimentally observe the superfluid transition by looking at the collective-mode spectrum. Our results are aimed at the present experimental effort to observe a superfluid phase transition in a trapped atomic Fermi gas.