Superradiant spin dynamics in a Bose-Einstein condensate coupled to an optical cavity

Dynamic transients are a natural ingredient of non-equilibrium quantum systems. One paradigmatic example is Dicke superradiance, describing the collectively enhanced population inversion of an ensemble of two-level atoms coupled to a single mode of the electromagnetic field.  Here, we present a new experimental approach, which exploits superradiance to engineer spin currents in a quantum gas via spontaneous Raman scattering in an optical cavity. The readout of the leaking photon field provides real-time access to the system’s self-consistent evolution.

Our experimental implementation is based on a ⁸⁷Rb spinor Bose-Einstein condensate which is coupled to a single mode of an ultrahigh finesse optical cavity. Two transverse laser fields incident on the atomic cloud give rise to cavity-assisted Raman transitions between different motional states of two adjacent spin levels. After benchmarking the collective nature of the elementary processes in this system, we investigate qualitatively different scenarios of superradiant spin dynamics. Our results pave the way to the exploration of dynamical gauge fields and transport phenomena in light-matter systems.