Distinguishability and many-particle interference

TL;DR

This paper investigates many-particle quantum interference, demonstrating that pairwise distinguishability is insufficient to describe three-photon interference, highlighting the importance of a collective triad phase in complex quantum systems.

Contribution

The study introduces the concept of a collective triad phase and experimentally shows its significance in three-photon interference, challenging the pairwise distinguishability paradigm.

Findings

Pairwise distinguishability does not fully determine three-photon interference.

The triad phase influences the interference behavior.

Experimental isolation of three-photon interference from two-photon effects.

Abstract

Quantum interference of two independent particles in pure quantum states is fully described by the particles' distinguishability: the closer the particles are to being identical, the higher the degree of quantum interference. When more than two particles are involved, the situation becomes more complex and interference capability extends beyond pairwise distinguishability, taking on a surprisingly rich character. Here, we study many-particle interference using three photons. We show that the distinguishability between pairs of photons is not sufficient to fully describe the photons' behaviour in a scattering process, but that a collective phase, the triad phase, plays a role. We are able to explore the full parameter space of three-photon interference by generating heralded single photons and interfering them in a fibre tritter. Using multiple degrees of freedom - temporal delays and polarisation - we isolate three-photon interference from two-photon interference. Our experiment disproves the view that pairwise two-photon distinguishability uniquely determines the degree of non-classical many-particle interference.