SPECTRAL LINEWIDTH NARROWING IN A STRONGLY COUPLED ATOM-CAVITY SYSTEMVIA SQUEEZED-LIGHT EXCITATION OF A VACUUM RABI RESONANCE

The system consisting of a two-level atom coupled strongly to a cavity mode behaves as a two-state system when excited near one of the ''vac uum'' Rabi resonances. With finite-bandwidth squeezed light incident u pon the cavity and tuned to one of these resonances, we show that it i s possible to realize a two-state system coupled to a squeezed vacuum. This system exhibits subnatural linewidths in the emitted spectra, as described by Gardiner [Phys. Rev. Lett. 56, 1917 (1986)] in a study o f spontaneous emission of a two-level atom in a squeezed vacuum, but r equires that only a single cavity mode be subject to squeezing rather than the entire three-dimensional vacuum.