Accessing the purity of a single photon by the width of the Hong-Ou-Mandel interference

TL;DR

This paper presents a method to measure the spectral purity of single photons using the width of Hong-Ou-Mandel interference, which relates to quantum coherence and does not require perfect mode matching.

Contribution

The authors introduce a technique that directly quantifies spectral purity of single photons via HOM dip width, independent of interference visibility.

Findings

The HOM dip width correlates with spectral purity and quantum coherence.

The method does not require perfect mode matching or high interference visibility.

It is especially effective for characterizing heralded single photon states.

Abstract

We demonstrate a method to determine the spectral purity of single photons. The technique is based on the Hong-Ou-Mandel (HOM) interference between a single photon state and a suitably prepared coherent field. We show that the temporal width of the HOM dip is not only related to reciprocal of the spectral width but also to the underlying quantum coherence. Therefore, by measuring the width of both the HOM dip and the spectrum one can directly quantify the degree of spectral purity. The distinct advantage of our proposal is that it obviates the need for perfect mode matching, since it does not rely on the visibility of the interference. Our method is particularly useful for characterizing the purity of heralded single photon states.