Coherence in a cold-atom photon switch

Abstract

We consider an all-optical photon switch in an atomic gas which is gated via a so-called Rydberg spin wave, i.e., a single Rydberg excitation that is coherently shared by the whole ensemble. A current challenge is to preserve the coherence of the Rydberg spin wave during the operation of the switch, which would enable, for example, its coherent optical readout. By employing a simple model description we investigate how the coherence of the Rydberg spin wave is affected during the operation of the switch. The coherence becomes increasingly protected with growing interatomic interaction strength. For the strongly interacting limit we derive analytical expressions for the spin-wave fidelity as a function of the optical depth and bandwidth of the incoming photon.