Optical response of a superfluid state in dilute atomic Fermi-Dirac gases

We theoretically study the propagation of light in a Fermi-Dirac gas in the presence of a superfluid state. BCS pairing between atoms in different spi n levels increases the optical linewidth and line shift of a quantum degene rate Fermi-Dirac gas already at very low densities and introduces a collisi onal local-field shift that may dramatically dominate the Lorentz-Lorenz sh ift. These optical properties could possibly signal the presence of the sup erfluid state and determine the value of the BCS order parameter. [S1050-29 47(99)50509-X].