The BCS-BEC Crossover

This chapter presents the crossover from the Bardeen-Cooper-Schrieffer (BCS) state of weakly-correlated pairs of fermions to the Bose-Einstein condensation (BEC) of diatomic molecules in the atomic Fermi gas. Our aim is to provide a pedagogical review of the BCS-BEC crossover, with an emphasis on the basic concepts, particularly those that are not generally known or are difficult to find in the literature. We shall not attempt to give an exhaustive survey of current research in the limited space here; where possible, we will direct the reader to more extensive reviews.Comment: 19 pages, 6 figures. This article will be published as Chapter 9 in "Quantum gas experiments - exploring many-body states", edited by P. Torma and K. Sengstock, Imperial College Press, London, to be published 201

Three-body correlations in a two-dimensional SU(3) Fermi gas

We consider a three-component Fermi gas that has SU(3) symmetry and is confined to two dimensions (2D). For realistic cold atomic gas experiments, we show that the phase diagram of the quasi-2D system can be characterized using two 2D scattering parameters: the scattering length and the effective range. Unlike the case in 3D, we argue that three-body bound states (trimers) in the quasi-2D system can be stable against three-body losses. Using a low-density expansion coupled with a variational approach, we investigate the fate of such trimers in the many-body system as the attractive interactions are decreased (or, conversely, as the density of particles is increased). We find that remnants of trimers can persist in the form of strong three-body correlations in the weak-coupling (high-density) limit.Comment: 13 pages, 4 figure

Evaporative depolarization and spin transport in a unitary trapped Fermi gas

We consider a partially spin-polarized atomic Fermi gas in a high-aspect-ratio trap, with a flux of predominantly spin-up atoms exiting the center of the trap. We argue that such a scenario can be produced by evaporative cooling, and we find that it can result in a substantially non-equilibrium polarization pattern for typical experimental parameters. We offer this as a possible explanation for the quantitative discrepancies in recent experiments on spin-imbalanced unitary Fermi gases.Comment: 6 pages, 3 figures; published versio