Sound in a strongly-interacting Fermi gas*

Sound propagation in an optically-trapped gas of strongly interacting fermionic $^6$Li atoms is studied. The atoms are prepared as a 50/50 mixture of the two lowest-energy internal states. Strong interactions are achieved by applying a magnetic field in the vicinity of a broad (834 G) s-wave Feshbach resonance. A sound wave is excited by locally applying a pulse of a repulsive blue-light potential. We measure the propagation of the excitation along the axial direction of the cigar-shaped cloud.