Cavity QED with a Bose-Einstein condensate

Cavity quantum electrodynamics (cavity QED) deals with the interaction of matter with the radiation field inside a resonator. In the regime of strong coupling a single atom--photon system coherently evolves over dynamically relevant timescales before the interaction with the environment leads to decohering processes. By strongly coupling a Bose-Einstein condensate (BEC) to the quantized field of a high-finesse optical cavity, we experimentally enter a new regime of cavity QED where all atoms couple identically and highly controlled to the cavity field. The collective nature of the internal state dynamics of this coupled BEC--cavity system is verified in the energy spectrum for a single excitation shared between BEC and cavity. In the far dispersive regime, the simultaneous coupling of all atoms to a single radiation mode gives rise to a highly nonlinear feedback mechanism between atomic motion and cavity field. We continuously monitor the coherent evolution of the driven system and find a degenerate matterwave to be requisite for the observed behavior. Besides its decisive relevance to the field of quantum information processing, the presented system offers a variety of interesting phenomena expected in the field of quantum gases within a quantum optical lattice.