Why only half of the fermionic atoms were converted to molecules by a Feshbach resonance?

Abstract

In some recent experiments an ultracold gas of ${}^{40}$K${}_2$ (or ${}^6$Li${}_2$) molecules has been produced from a degenerate two-component Fermi gas of ${}^{40}$K (or ${}^6$Li) atoms by adiabatic passage through a Feshbach resonance. The maximum atom-molecule transfer efficiency is reported to be about 50%. We propose a simple microscopic model to characterize the ground state of the gas in the vicinity of the resonance, and show that the term describing the atom-molecule coupling is responsible for the observed efficiency 50%. Our result also suggests that the experiments have produced a molecular condensate.

4 pages + 2 figures