Non-Reciprocal Amplification of Light Using Cold Atoms Coupled to an Optical Nanofiber

Abstract

Optical nanofibers realized as the waist of tapered silica fibers can be used to trap and optically interface laser-cooled atoms. Building on this system, we experimentally show a novel scheme for the nonreciprocal Raman amplification of light. While typically either the magneto-optical effect, a temporal modulation or an optical nonlinearity is employed to break reciprocity, in our approach, this results from the spin of the atoms forming the gain medium. By taking advantage of the inherent spin-momentum locking present in optical nanofibers, we perform an experiment in which we set the amplification direction by a suitable preparation of the atomic spin state. Our approach is general and, suitable quantum emitters provided, could also be implemented beyond the optical domain of the electromagnetic spectrum.