Improving On-Demand Single Photon Source Coherence and Indistinguishability Through a Time-Delayed Coherent Feedback

Single photon sources (SPSs) are an essential resource for many quantum information technologies. We demonstrate how the inclusion of time-delayed coherent feedback in a scalable waveguide system, can significantly improve the two key SPS figures of merit: coherence and indistinguishability. Our feedback protocol is simulated using a quantum trajectory discretized waveguide model which can be used to directly model Hanbury Brown and Twiss (HBT) and Hong-Ou-Mandel (HOM) interferometers. With the proper choice of the round trip phase, the non-Markovian dynamics from the time-delayed feedback improves the indistinguishability of the SPS by up to 57%. We also show how this mechanism suppresses the detrimental effects of off-chip decay and pure dephasing.