Local observation of pair condensation in a Fermi gas at unitarity

Phys Rev Lett. 2014 Mar 14;112(10):100404. doi: 10.1103/PhysRevLett.112.100404. Epub 2014 Mar 13.

Abstract

We present measurements of the local (homogeneous) density-density response function of a Fermi gas at unitarity using spatially resolved Bragg spectroscopy. By analyzing the Bragg response across one axis of the cloud, we extract the response function for a uniform gas which shows a clear signature of the Bose-Einstein condensation of pairs of fermions when the local temperature drops below the superfluid transition temperature. The method we use for local measurement generalizes a scheme for obtaining the local pressure in a harmonically trapped cloud from the line density and can be adapted to provide any homogeneous parameter satisfying the local density approximation.