Superfluid Expansion of a Strongly Interacting Fermi Gas

We study the expansion of a rotating, superfluid Fermi gas. The presence and absence of vortices in the rotating gas is used to distinguish superfluid and normal parts of the expanding cloud. We find that the superfluid pairs survive during the expansion until the density decreases below a critical value. Our observation of superfluid flow at this point extends the range where fermionic superfluidity has been studied to densities of 1.2 10^{11} cm^{-3}, about an order of magnitude lower than any previous study.