The second-order intensity correlation function of light transmitted out of a cavity QED system exhibits the nonclassical features and dynamics of the atom-field interaction. We present measurements of the intensity correlation to examine the size of the nonclassical features and the dependence on driving intensity, detuning, and the strength of the atom-field coupling. We use a model that takes into account experimental conditions to achieve a quantitative agreement with the observations. PACS number͑s͒: 42.50.Dv, 42.50.Ct, 32.80.Ϫtwhere is the transition dipole moment, is the transition frequency, and V is the cavity mode volume. There are three PHYSICAL REVIEW A, VOLUME 61, 053821

We measure the transmission spectrum of an optical cavity filled with two-level atoms. For small intensities, the coupling between atoms and a single mode of the cavity splits the spectrum into two normal modes: the vacuum Rabi peaks. We gradually decouple the system in two ways and study the evolution of the vacuum Rabi peaks. First we lower the atom-cavity coupling frequency through its intensity dependence, showing that the peaks shift, deform, exhibit frequency hysteresis, and eventually merge into a single peak that approaches the empty cavity resonance. Second we detune the atoms and the cavity mode and observe an avoided crossing. The normal modes of the coupled system transform into the two resonances of the uncoupled system. We map out the transition region and find good agreement with theoretical predictions.

We report nonclassical correlations in the light transmitted by a collection of two-level atoms strongly coupled to a single mode of the electromagnetic field of a driven optical cavity. This cavity QED system can produce bunched light that violates the Schwarz inequality due to the state preparation of the system from the detection of a photon. The correlation function shows oscillations at a frequency that decreases with increasing intensity. [S0031-9007(98)05998-5] PACS numbers: 42.50.Dv, 42.50.Ct An ideal environment to study nonclassical electromagnetic fields is a system consisting of one or more two-level atoms coupled to a single mode of the electromagnetic field of an optical resonator. This system, originally studied by Jaynes and Cummings [1], has become the arena of cavity quantum electrodynamics (QED). Recent explorations of the effects of strong coupling between atom and cavity include the vacuum Rabi splitting for an atom in an optical cavity [2], the micromaser [3], the microlaser [4], and