Narrowband Photon Pairs From A Cold Atomic Vapour For Interfacing With A Single Atom

Abstract

We present a narrowband and a bright source of time correlated photon pairs based on a cold cloud of 87Rb atoms via a non-degenerate fourwave mixing process. The bandwidth of the generated photons can be tuned from 10 MHz?30 MHz by changing the optical density of the atomic cloud. The violation of the Cauchy-Schwarz inequality by a factor of 50?10^6 strong non-classical correlation between the generated fields with a maximum instantaneous pair detection rate of 20,000 pairs/s. The generated photon pairs are entangled in the polarisation degree of freedom. The bandwidth and wavelength of the generated photons are suitable to interface with 87Rb atoms, a common workhorse for quantum memories. As a first step towards interfacing, we have performed a Hong-Ou-Mandel interference experiment between a single photon from a single 87Rb atom and a heralded single photon from our source. The experiment demonstrates indistinguishability of single photons generated from two different physical systems which is an important step towards establishing quantum networks.