Gain components in the Autler-Townes doublet from quantum interferences in decay channels

Abstract

We consider nondegenerate pump-probe spectroscopy of $V$ systems under conditions such that interference among decay channels is important. We demonstrate how this interference can result in new gain features instead of the usual absorption features. We relate this gain to the existence of a new vacuum induced quasi-trapped-state. We further show how this also results in a large refractive index with low absorption.