Quantum frequency combs and Hong-Ou-Mandel interferometry: the role of spectral phase coherence

TL;DR

This paper investigates how Hong-Ou-Mandel interferometry interacts with quantum frequency combs, revealing that spectral phase coherence does not influence the interference pattern and cannot detect high-dimensional frequency-bin entanglement.

Contribution

It demonstrates that Hong-Ou-Mandel interference is insensitive to spectral phase differences in quantum frequency combs, clarifying limitations in entanglement detection.

Findings

Interference is insensitive to relative phase between comb line pairs.

Hong-Ou-Mandel fringes do not reveal high-dimensional entanglement.

Spectral phase coherence does not affect two-photon interference patterns.

Abstract

The Hong-Ou-Mandel interferometer is a versatile tool for analyzing the joint properties of photon pairs, relying on a truly quantum interference effect between two-photon probability amplitudes. While the theory behind this form of two-photon interferometry is well established, the development of advanced photon sources and exotic two-photon states has highlighted the importance of quantifying precisely what information can and cannot be inferred from features in a Hong-Ou-Mandel interference trace. Here we examine Hong-Ou-Mandel interference with regard to a particular class of states, so-called quantum frequency combs, and place special emphasis on the role spectral phase plays in these measurements. We find that this form of two-photon interferometry is insensitive to the relative phase between different comb line pairs. This is true even when different comb line pairs are mutually coherent at the input of a Hong-Ou-Mandel interferometer, and the fringe patterns display sharp temporal features. Consequently, Hong-Ou-Mandel interference cannot speak to the presence of high-dimensional frequency-bin entanglement in two-photon quantum frequency combs.