Bose polaron interactions in a cavity-coupled monolayer semiconductor

TL;DR

This study investigates Bose polarons in a monolayer semiconductor within an optical cavity, revealing tunable interactions and the first direct measurement of polaron-polaron interaction strength in a nonequilibrium, driven-dissipative system.

Contribution

It demonstrates the control of Bose polaron interactions via a biexciton Feshbach resonance in a 2D semiconductor cavity system, introducing a new platform for many-body physics.

Findings

Observation of two new quasiparticle branches.

Polaron interactions can switch from repulsive to attractive.

First direct measurement of Bose polaron-polaron interaction strength.

Abstract

The interaction between a mobile quantum impurity and a bosonic bath leads to the formation of quasiparticles, termed Bose polarons. The elementary properties of Bose polarons, such as their mutual interactions, can differ drastically from those of the bare impurities. Here, we explore Bose polaron physics in a two-dimensional nonequilibrium setting by injecting $\sigma^-$ polarised exciton-polariton impurities into a bath of coherent $\sigma^+$ polarised polaritons generated by resonant laser excitation of monolayer MoSe$_2$ embedded in an optical cavity. By exploiting a biexciton Feshbach resonance between the impurity and the bath polaritons, we tune the interacting system to the strong-coupling regime and demonstrate the coexistence of two new quasiparticle branches. Using time-resolved pump-probe measurements we observe how polaron dressing modifies the interaction between impurity polaritons. Remarkably, we find that the interactions between high-energy polaron quasiparticles, that are repulsive for small bath occupancy, can become attractive in the strong impurity-bath coupling regime. Our experiments provide the first direct measurement of Bose polaron-polaron interaction strength in any physical system and pave the way for exploration and control of many-body correlations in driven-dissipative settings.