The role of pump coherence in two-photon interferometry

TL;DR

This paper investigates how pump coherence affects two-photon interferometry by using a short-coherence CW laser in a regime between traditional long-coherence and pulsed experiments, revealing the importance of pump coherence.

Contribution

It demonstrates the intermediate coherence regime in two-photon interferometry and highlights the role of pump coherence using a CW diode laser with a Mach-Zehnder interferometer.

Findings

Coherence between two-photon amplitudes is induced by the interferometer.

Remaining incoherent amplitudes are not eliminated due to CW nature.

Pump coherence significantly influences two-photon interference patterns.

Abstract

We use a parametric down-conversion source pumped by a short coherence-length continuous-wave (CW) diode laser to perform two-photon interferometry in an intermediate regime between the more familiar Franson-type experiments with a long coherence-length pump laser, and the short pulsed pump "time-bin" experiments pioneered by Gisin's group. The use of a time-bin-like Mach-Zehnder interferometer in the CW pumping beam induces coherence between certain two-photon amplitudes, while the CW nature of the experiment prevents the elimination of remaining incoherent ones. The experimental results highlight the role of pump coherence in two-photon interferometry.