Ground state bistability of cold atoms in a cavity

We report on our recent experiments performed with cold atoms strongly coupled to a single mode of a high-finesse optical cavity. We demonstrate an optical bistability between two hyperfine ground states of the atoms.

While the atomic saturation is kept low, the source of nonlinearity is a cavity-assisted pumping between ground states of the atoms and the stability depends on the intensity of two driving lasers. We interpret the phenomenon in terms of the recent paradigm of driven-dissipative phase transitions, where the transmitted and driving fields are understood as the order and control parameters, respectively. Furthermore, we explore the radiation properties of light scattered by atoms into the cavity when they are in a subradiant configuration.