Toward heralded single-photon storage via chiral cavity-enhanced spontaneous Raman scattering

We propose a scheme of heralded storages of single photons via spontaneous Raman scattering (SRS) enhanced by a chiral standing-wave cavity, which creates a non-classically correlated pair of a spin wave and a Stokes photon (heralded photon) when a single-photon “write” pulse is applied to an atomic ensemble. In this scheme, to decrease the power of the write pulse for SRS, the write laser and the Stokes fields are aligned to propagate near-collinearly through the atoms. The short storage lifetime remains a challenge in standing-wave cavity-enhanced SRS. To prolong the storage lifetime, we achieve a long-wavelength spin-wave memory by removing the backward-scattering Stokes field from the cavity, which is realized by using non-reciprocal couplings between the Stokes fields and the atoms. In the experiment, the memory lifetime is demonstrated up to ∼100 μs, which is beyond the limitation (∼350 ns) of the storage in the atomic ensembles coupled to standing-wave cavities. We achieve a spin-wave memory for the write pulse containing a mean photon number of ∼4. The quantum correlation of the Stokes-spin-wave pairs is beyond 2, which gives strong evidence of non-classical behavior.