Critical velocity and dissipation of an ultracold Bose-Fermi counterflow

Superfluidity is amongst the most impressive macroscopic manifestations of quantum behavior. Frictionless flow has been observed in several low-temperature quantum systems, such as liquid helium [1, 2], or more recently ultracold gases [3-5]. Several hallmarks of superfluidity such as critical velocity, quantized vortices, and second sound have been observed [6-11], in both liquid helium and ultracold gases, and in both Bose and Fermi systems.