Cavity electromagnetically induced transparency (EIT) in a coherently prepared cavity-atom system is manifested as a narrow transmission peak of a weak probe laser coupled into the cavity mode. We show that, with a resonant pump laser coupling the cavity-confined four-level atoms from free space, the narrow transmission peak of the cavity EIT is split into two peaks. The two peaks represent the dressed intracavity dark states and have a frequency separation approximately equal to the Rabi frequency of the free-space pump laser. We experimentally observed the dressed intracavity dark states in cold Rb atoms confined in a cavity, and the experimental results agree with theoretical calculations based on a semiclassical analysis.

• Received 22 September 2011

DOI:https://doi.org/10.1103/PhysRevA.85.013814