Comment on "Coherence measures for heralded single-photon sources"

TL;DR

This paper critiques a recent study on coherence measures in heralded single-photon sources, clarifying that the claimed one-arm second-order effect was not actually measured, thus questioning the original conclusions.

Contribution

It provides a critical analysis of the previous work, correcting the misunderstanding about the measured coherence effects in heralded photon sources.

Findings

No one-arm second-order effect was measured in the referenced study.

The critique clarifies the distinction between different coherence measures.

Highlights the importance of accurate interpretation of experimental results.

Abstract

A recent Brief Report [Phys. Rev. A 79, 035801 (2009)] investigates two figures of merit for heralded photon sources based on spontaneous parametric down-conversion with a continuous pump, namely the time-averaged temporal coherence between the signal and idler beams and the time-averaged conditioned second-order degree of coherence for photons in the heralded arm. However, contrary to what is claimed, no one-arm second-order effect is actually measured.