Tunable coherent and dissipative superradiant dynamics in a spinor quantum gas*

Dissipative and coherent processes are at the core of the evolution of many-body systems. Their competition and interplay can lead to new phases of matter, instabilities, and complex non-equilibrium dynamics. However, probing these phenomena at a microscopic level in a setting of well-defined, controllable coherent and dissipative couplings often proves challenging. In our setup, we realize such a quantum many-body system using a ⁸⁷Rb spinor Bose-Einstein condensate (BEC) strongly coupled to a single optical mode of a lossy cavity. Two transverse laser fields incident on the BEC allow for cavity-assisted Raman transitions between different motional states of two neighboring spin levels.

In a first set of experiments, adjusting the imbalance between the drives enables us to tune the competition between coherent dynamics and dissipation, with the appearance of a dissipation-stabilized phase and bistability. We relate the observed phases to microscopic elementary processes in the open system by characterizing the properties of the underlying polariton modes. Moreover, we report on recent results showing collective spin dynamics in a cavity via superradiant Raman scattering. We identify the collective nature of the transitions and leverage the leaking photon field to gain real-time, non-destructive readout of the system's dynamics. Together, our results open new avenues for investigating non-Hermitian systems, spin-orbit coupling in dissipative settings, and transport phenomena in light-matter systems.