Hong-Ou-Mandel interference of two independent continuous-wave coherent photons

TL;DR

This paper demonstrates Hong-Ou-Mandel interference between two independent continuous-wave coherent photons using high-precision frequency stabilization, showing robustness over distance and observing interference fringes even with large frequency differences.

Contribution

First experimental demonstration of HOM interference with independent CW coherent sources stabilized without synchronization or shared reference.

Findings

Successful observation of HOM interference fringe with independent lasers

Detection of two-photon beating when frequency difference exceeds spectral bandwidth

Robustness of the interference over varying source separation distances

Abstract

Interference between two completely independent photons lies at the heart of many photonic quantum information applications such as quantum repeaters, teleportation, and quantum key distribution. Here, we report the observation of Hong-Ou-Mandel (HOM) interference with two independent continuous-wave coherent light sources that are neither synchronized nor share any common reference. To prepare highly indistinguishable photons from two independent laser sources, we employ high-precision frequency-stabilization techniques using the 5S1/2(F=3)-5P1/2(F'=3) transition line of 85Rb atoms. We successfully observe a HOM interference fringe with two independent continuous-wave coherent photons originating from either the frequency-locked and frequency-modulated lasers. An interference fringe involving two-photon beating is also observed when the frequency difference between the two interfering photons is beyond the spectral bandwidth of the individual coherent photons. We carry out further experiments to verify the robustness of the source preparation regardless of the separation distance between the two independent photon sources.