Narrowband Correlated Photon Quadruplets From a Cold Atomic Ensemble

We demonstrate a bright correlated photon-pair source using double-A four-wave mixing in a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">87</sup>Rb cold atomic ensemble prepared in a magneto-optical trap. A counter-propagating pump configuration, combined with the small-angle collection along the propagation direction, enables clear distinction of resulting Stokes (780nm) and anti-Stokes (795nm) photons from pump fields. From measurements, we infer a generation rate of correlated photon pairs up to 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> count per second (cps) into a collection mode waist of 175 μm. This is competitive with previous results observed in cold atomic ensembles [1], [2]. Their narrow spectral bandwidth makes these photons highly suitable for direct interaction with atomic systems and long-distance fiber transmission.