Nonlinear spectroscopy in the strong-coupling regime of cavity QED

Abstract

A nonlinear spectroscopic investigation of a strongly coupled atom-cavity system is presented. A two-field pump-probe experiment is employed to study nonlinear structure as the average number of intracavity atoms is varied from $\overline{N}\ensuremath{\approx}4.2$ to $\overline{N}\ensuremath{\approx}0.8$. Nonlinear effects are observed for as few as $0.1$ intracavity pump photons. A detailed semiclassical simulation of the atomic beam experiment gives reasonable agreement with the data for $\overline{N}\ensuremath{\gtrsim}2$ atoms. The simulation procedure accounts for fluctuations in atom-field coupling which have important effects on both the linear and nonlinear probe transmission spectra. A discrepancy between the simulations and the experiments is observed for small numbers of atoms $(\overline{N}\ensuremath{\lesssim}1)$. Unfortunately, it is difficult to determine if this discrepancy is a definitive consequence of the quantum nature of the atom-cavity coupling or a result of the severe technical complications of the experiment.