Control-laser-induced subnatural linewidths and quenching of spontaneous emission

Abstract

We show how control lasers lead to subnatural linewidths in spontaneous emission as well as to the quenching of the quantum noise. We trace this quenching to the dispersive contributions to the line shape. We obtain analytical expressions for linewidths that for Λ systems are half the natural linewidths with the possibility of much more reduction for detuned control laser. We further present a simple physical analysis in terms of a two-photon Fermi golden rule to understand cancellation of spontaneous emission. Finally, we relate our results to recent experiments.