A Study Of Fermionic Superfluid

Ultracold quantum gases and artificial gauge fields have emerged as an excellent platform to explore many-body systems and to simulate novel phases of matter.One of the most re-markable achievements is the realization of interacting two-component Fermi gases undergoing the smooth crossover from Bose-Einstein condensates(BECs)to Bardeen-Cooper-Schrieffer(BCS)superfluids.Universal physical behaviors emerge at the unitary limit,which represents a strongly interacting system ideal for testing many-body theories.Hallmarks of superfluidity such as frictionless flows,quantized vortices and second sound have been observed in cold atoms.We develop a method to extract the dissipation for a heavy moving impurity immersed in superfluid Fermi gases,which may serve as a theoretical model to explain relevant experiments.The drag force is derived analytically.As a reward,we are able to extract the density-density correlation function,from which density excitations of the system are carefully examined.We show that dissipations through drag force is associated with two types of excitations,one being single-particle and the other being collective.We map out the critical velocity for dissipation across the BEC-BCS crossover,consistent with existing experiments.For a magnetic impurity,we show that the dissipation is immune to collective excitations.Our study clearly manifests that dissipation and associated excitations can be controlled by coupling superfluid Fermi gases with a moving impurity,and paves the way for further exploring intriguing realm of nonequi-librium phenomena and dissipation dynamics.