Symmetry breaking and non-ergodicity in a driven-dissipative ensemble of multilevel atoms in a cavity

Abstract

Dissipative light-matter systems can display emergent collective behavior. Here, we report a Z_{2}-symmetry-breaking phase transition in a system of multilevel ^{87}Rb atoms strongly coupled to a weakly driven two-mode optical cavity. In the symmetry-broken phase, nonergodic dynamics manifests in the emergence of multiple stationary states with disjoint basins of attraction. This feature enables the amplification of a small atomic population imbalance into a characteristic macroscopic cavity transmission signal. Our experiment does not only showcase strongly dissipative atom-cavity systems as platforms for probing nontrivial collective many-body phenomena, but also highlights their potential for hosting technological applications in the context of sensing, density classification, and pattern retrieval dynamics within associative memories.