Optimizing the quantum interference between single photons and local oscillator with photon correlations

The quantum interference between a coherent state and a single photon is an important tool in continuous variable optical quantum technologies to characterize and engineer non-Gaussian quantum states. Semiconductor quantum dots (QDs), which have recently emerged as a key platform for efficient single-photon generation, could become interesting assets in this context. An essential parameter for interfering single photons and classical fields is the mean wavepacket overlap between both fields. Here, we report on two homodyne photon-correlation techniques enabling the precise measurement of the overlap between a single photon generated by a QD-cavity device and pulsed laser light. The different statistics of interfering fields lead to specific signatures of the quantum interference on the photon correlations at the output of the interfering beam splitter. We compare the behavior of maximized overlap, measuring either the Hong–Ou–Mandel visibility between both outputs or the photon bunching at a single output. Through careful tailoring of the laser light in various degrees of freedom, we achieve a record overlap of 76 % with integrated solid-state sources, which evidences the very low level of noise in our integrated single-photon sources.