Spin drag and fast response in a quantum mixture of atomic gases

TL;DR

This paper investigates the immediate response of a second component in a quantum fluid mixture to a sudden perturbation, revealing how short-time dynamics and interaction effects influence spin drag phenomena across various quantum systems.

Contribution

It introduces a perturbation theory framework linking short-time response to the crossed dynamic structure factor and identifies regimes of fast spin drag sensitive to Hamiltonian interactions.

Findings

Response fixed by energy weighted moment of crossed dynamic structure factor

Identification of fast spin drag regimes influenced by interaction effects

Explicit calculation of low frequency excitations' contribution to the f-sum rule

Abstract

By applying a sudden perturbation to one of the components of a mixture of two quantum fluids, we explore the effect on the motion of the second component on a short time scale. By implementing perturbation theory, we prove that for short times the response of the second component is fixed by the energy weighted moment of the crossed dynamic structure factor (crossed f-sum rule). We also show that by properly monitoring the time duration of the perturbation it is possible to identify peculiar fast spin drag regimes, which are sensitive to the interaction effects in the Hamiltonian. Special focus is given to the case of coherently coupled Bose-Einstein condensates, interacting Bose mixtures exhibiting the Andreev-Bashkin effect, normal Fermi liquids and the polaron problem. The relevant excitations of the system contributing to the spin drag effect are identified and the contribution of the low frequency gapless excitations to the f-sum rule in the density and spin channels is explicitly calculated employing the proper macroscopic dynamic theories. Both spatially periodic and Galilean boost perturbations are considered.