We calculate intensity autocorrelations and cross correlations for the light transmitted from a system consisting of a three-level Λ-type atom inside an optical cavity that supports two orthogonally polarized modes with one mode of the cavity weakly driven on resonance. We also include damping of the cavity modes and spontaneous emission from the atom using the framework of quantum trajectory theory. The correlation functions are compared with those of a two-level atom/cavity system as the coupling to the third level is increased, and we find a transition from photon bunching to photon antibunching. The three-level model allows the atom to couple to both field modes for which we calculate intensity cross correlations that exhibit nonclassical behaviors. Finally, we discuss the lack of entanglement between the field modes despite their common coupling to the same atom and the presence of atom-field entanglement.
We calculate the probe spectrum for multilevel atoms in a damped, weakly driven cavity supporting two degenerate orthogonally polarized modes. One mode is weakly driven by a linearly polarized external field. The atoms, initially prepared in a
mF=0 hyperfine ground state, couple to the driven mode by making a $\ensuremath{\Delta}{m}_{F}=0$ transition and to the orthogonally polarized mode by making $\ensuremath{\Delta}{m}_{F}=\ifmmode\pm\else\textpm\fi{}1$ transitions to other hyperfine sublevels. We compare probe spectra, the intensity of the driven mode, the undriven mode, and the atomic excitation probability as a function of the detuning of the driving laser from the cavity resonance for three- and four-level atomic models. In both cases the spectrum of the driven mode is a vacuum Rabi doublet familiar from the driven, damped Jaynes-Cummings model. The undriven mode spectrum is a triplet with the maximum on resonance for the three-level model while the four-level model has a four-peaked spectrum. We discuss the role of strong coupling to the undriven mode in accounting for the qualitative difference between the models.