Sound wave propagation in strongly elongated fermion clouds at finite collisionality

P. CAPUZZI; P. VIGNOLO; F. FEDERICI; M. P. TOSI

Buenos Aires

Conferencia; 13th International Conference on "Recent Progress in Many-Body Theories"; 2005

Universidad de Buenos Aires

We consider a mixture of ultracold fermions confined in an elongated cigar-shaped trap where a density perturbation is generated by a laser beam focused at the center of the trap. We calculate the one-body distribution functions of the fermions by solving the Vlasov-Landau equations and analyze their evolution for various trap anisotropies and fermion-fermion interaction strengths. In particular, we consider strongly repulsive and strongly attractive couplings and calculate the velocity of propagation of the density waves. We find that the speed of sound decreases by increasing the interaction strength in both the strongly repulsive and attractive mean-field limits, consistently with the transition from zero to first sound. For attractive couplings we also use hydrodynamic equations to study the propagation of first sound in a superfluid Fermi gas with main attention to the transition from the mean-field BCS to the unitarity regime. We find that the speed of sound differs by a factor sqrt{3/5} from that in a homogeneous three-dimensional superfluid. The predictions of the theory could be tested by measurements of sound-wave propagation in a set-up such as that exploited by M.R. Andrews et al. [Phys. Rev. Lett. 79, 553 (1997)] for an atomic Bose-Einstein condensate.