Mediated interactions in mixtures of ultracold atoms

TL;DR

This paper reviews recent theoretical and experimental advances in mediated interactions within ultracold atom mixtures, highlighting how particle-hole and phonon excitations induce tunable long-range interactions that can lead to phenomena like fermion superfluidity.

Contribution

It presents new experimental observations of mediated interactions in a Cs-Li mixture and compares them with theoretical models, demonstrating control over long-range interactions in quantum gases.

Findings

Fermion-mediated attractions between bosons confirmed experimentally.

Observation of suppression and revival of sound modes in strong-coupling regime.

Agreement between experimental results and theoretical predictions in weak-coupling regime.

Abstract

We describe recent theoretical and experimental developments on mediated interactions in mixtures of bosonic and fermionic atoms. We discuss how particle-hole excitations of a Fermi sea can induce long-range interactions between heavy impurities or atoms in a Bose-Einstein condensate. Conversely, phonon excitations of a Bose-Einstein condensate induce interactions between fermionic atoms. These mediated interactions exhibit different short-range and long-range scaling regimes with distance and, if strong enough, can induce fermion superfluidity. We discuss the prospects for observing new phenomena that could arise from mediated interactions. Experimentally, we outline recent studies of the 133Cs-6Li Bose-Fermi mixture, a platform well-suited for investigating fermion-mediated interactions. A Cs Bose-Einstein condensate immersed in a degenerate Li Fermi gas is prepared with tunable interspecies interactions. In the weak-coupling regime, precision measurements of condensate properties reveal fermion-mediated attractions between bosons, matching theoretical predictions. In the strong-coupling regime, we observe suppression and revival of sound modes and novel many-body resonances. Altogether, we aim to highlight both instances where experiment and theory agree well, and promising prospects to engineer long-range interactions in atomic quantum gases.