Séminaire du LPTMS: Gregory Astrakharchik

Andreev-Bashkin Effect in quantum gases

Gregory Astrakharchik (UPC, Barcelona)

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. We quantify the non-dissipative drag effect, resulting from the Andreev-Bashkin current-current interaction between the two components of the gas, and we show that in the regime of strong coupling it causes a significant suppression of the spin-wave velocity.

[1] L. Parisi, G. E. Astrakharchik, and S. Giorgini,
Spin Dynamics and Andreev-Bashkin Effect in Mixtures of One-Dimensional Bose Gases,
Phys. Rev. Lett. 121, 025302 (2018)

[2] Jacopo Nespolo, Grigori E. Astrakharchik, Alessio Recati,
Andreev-Bashkin effect in superfluid cold gases mixture,
New J. Phys. 19, 125005 (2017)

Date/Time : 16/04/2019 - 11:00 - 12:00

Location : LPTMS, salle 201, 2ème étage, Bât 100, Campus d'Orsay

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