Abstract
The authors show that the Andreev-Bashkin drag between two superfluid species is proportional to current-current response functions and compute its effect on the spin speed of sound in a homogeneous mixture, the dipole mode in a trapped gas and the dipole response after a fast perturbation.
Highlights
The superfluid drag was predicted by Andreev and Bashkin [1] for a two component superfluid mixture, correcting previous works by Khalatnikov [2]
In analogy with the single component case the superfluid densities can be expressed in terms of transverse current-current response functions
A striking result that has no analogy with the single component case is that, while the overall response of the superfluid to a transverse vector field vanishes at zero temperature, such a field will give rise nonzero response even at vanishing temperature when acting only on one component
Summary
The superfluid drag was predicted by Andreev and Bashkin [1] for a two component superfluid mixture, correcting previous works by Khalatnikov [2]. In particular we relate the superfluid drag density to the current-current response functions, making a clear distinction between their transverse and longitudinal long wavelength limits This approach applies to any quantum mixture in the linear response regime. It can be employed to predict the magnitude of the drag effect in a variety of systems such as Bose-Bose superfluid mixtures on a lattice, Bose-Fermi superfluid mixtures, and Fermi-Fermi superfluid mixtures We connect this result with the formalism of sum rules, which is an established tool to study the elementary and collective excitations of (trapped) quantum gases
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