Andreev-Bashkin effect in superfluid cold gases mixture

TL;DR

This paper investigates the Andreev-Bashkin effect in superfluid mixtures, revealing how interspecies interactions influence sound velocities, susceptibilities, and stability, supported by theoretical analysis and quantum Monte Carlo simulations.

Contribution

It provides a comprehensive analysis of the Andreev-Bashkin effect in superfluid mixtures, including its impact on dynamic properties and stability, using quantum hydrodynamics, perturbation theory, and simulations.

Findings

Drag affects spin channel but not density channel.

Spin phonons do not satisfy the usual Bijl-Feynman relation.

Entrainment influences the dynamical stability of superfluid mixtures.

Abstract

We study a mixture of two superfluids with density-density and current-current (Andreev-Bashkin) interspecies interactions. The Andreev-Bashkin coupling gives rise to a dissipationless drag (or entrainment) between the two superfluids. Within the quantum hydrodynamics approximation, we study the relations between speeds of sound, susceptibilities and static structure factors, in a generic model in which the density and spin dynamics decouple. Due to translational invariance, the density channel does not feel the drag. The spin channel, instead, does not satisfy the usual Bijl-Feynman relation, since the f-sum rule is not exhausted by the spin phonons. The very same effect on one dimensional Bose mixtures and their Luttinger liquid description is analysed within perturbation theory. Using diffusion quantum Monte Carlo simulations of a system of dipolar gases in a double layer configuration, we confirm the general results. Given the recent advances in measuring the counterflow instability, we also study the effect of the entrainment on the dynamical stability of a superfluid mixture with non-zero relative velocity.