Dissipationless flow in a Bose-Fermi mixture

Mixtures of quantum fluids lie at the forefront of research into strongly-correlated quantum matter as they exhibit a rich many-body phase diagram. We study the dynamics of spin-polarized fermionic impurities immersed in a (superfluid) BEC via their collective excitations. We observe a dissipationless flow of the fermions, from the non-interacting to the strong-coupling regime where the impurities inherit the hydrodynamic modes of the BEC. We further probe the systems response as a function of temperature observing the fermions' transition from the collisionless to the hydrodynamic regime right at the superfluid transition temperature. Our experiments demonstrate the ability to pristinely control the fluid dynamics of a Bose-Fermi mixture in a dual-species ultracold atomic gas experiment.