# Direct observation of phase sensitive Hong-Ou-Mandel interference

## TL;DR

This paper introduces a phase-sensitive measurement method to evaluate both the quality and coherence of single photons, revealing their particle and wave interference aspects through a novel witness tested experimentally.

## Contribution

It develops a new witness based on conditional nonclassical squeezing that simultaneously assesses photon quality and indistinguishability, overcoming phase insensitivity limitations.

## Key findings

- Successfully demonstrated the witness with on-demand single photons
- Revealed both particle and wave aspects of quantum interference
- Provided a more comprehensive photon interference assessment

## Abstract

Quality of individual photons and their ability to interfere is traditionally tested by measuring the Hong-Ou-Mandel photon bunching effect. However, this phase insensitive measurement only tests the particle aspect of the quantum interference. Motivated by these limitations, we formulate a witness capable of recognizing both the quality and the coherence of two photons from a single set of measurements. We exploit the conditional nonclassical squeezing which is sensitive to both the quality of the single photons and their indistinguishability and we show that it can be used to irectly reveal both the particle and the wave aspects of the quantum interference. Finally, we experimentally test the witness by applying it to a pair of independent single photons generated on demand.