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.