Controlling the competition between coherent and dissipative processes in a superradiant quantum gas

Exposing a many-body system to external drives and losses can deeply modify its phases. Beside their fundamental interest, driven-dissipative systems prompt new paradigms for material engineering. A prime example is given by hybrid systems in which tuning of the elementary excitations is obtained by coupling matter to light. In this perspective, gaining conceptual understanding on how the microscopic properties of such systems can be tuned by the coupling to the environment is of primary interest. However, it is often a challenge to find platforms combining well-defined, tunable coherent and dissipative channels and, at the same time, the access to microscopic observables of the system. We report on a synthetic many-body system offering these possibilities, based on a Bose-Einstein condensate that is strongly coupled to an optical cavity. In our experiment, both spin and momentum of the atoms are coupled to the lossy cavity mode via two independent external Raman drives. Adjusting the imbalance between the drives allows to tune the competition between coherent dynamics and dissipation, with the appearance of a dissipation-stabilized phase and bistability. We characterize the properties of polariton modes and relate the observed phases to the microscopic elementary processes in the open system. Our findings provide prospects for studying squeezing in non-Hermitian systems, quantum jumps in superradiance, and dynamical spin-orbit coupling in a dissipative setting.