Probing colored noise from the index of refraction of strongly driven two-level atoms

Abstract

We analyze the effects of a reservoir having a generic spectrum (colored noise) on the index of refraction of a system of strongly driven two-level atoms (gas) probed by a weak field. We show that for high Rabi frequencies, $\ensuremath{\Omega},$ a simple analytic expression results for the susceptibility function (with respect to the probe) when $\ensuremath{\nu}\ensuremath{\approx}\ensuremath{\Omega},$ where $\ensuremath{\nu}$ is the detuning between driving and probe fields frequencies. Several distinct features are revealed in that function when compared to the one resulting from a reservoir with a white-noise spectrum (atom-vacuum coupling). We also show that the Mach-Zehnder interferometry could permit distinguishing between the two kinds of spectra and we point out the sensitive dependence of the index of refraction of the atomic gas on $\ensuremath{\Omega}$ and find a signature for the non-Markovian evolution.