Observation of genuine three-photon interference

TL;DR

This paper reports the first experimental observation of genuine three-photon interference using energy-time entangled triplets, demonstrating strong three-particle correlations in an interferometric setup.

Contribution

It presents the first realization of a three-photon GHZ interferometer, showcasing genuine three-particle interference not reducible to two-photon effects.

Findings

Achieved 90.5% visibility in three-photon interference fringes.

Demonstrated phase-dependent variation of three-photon coincidences.

Provided new tools for multiphoton quantum information and fundamental tests.

Abstract

Multiparticle quantum interference is critical for our understanding and exploitation of quantum information, and for fundamental tests of quantum mechanics. A remarkable example of multi-partite correlations is exhibited by the Greenberger-Horne-Zeilinger (GHZ) state. In a GHZ state, three particles are correlated while no pairwise correlation is found. The manifestation of these strong correlations in an interferometric setting has been studied theoretically since 1990 but no three-photon GHZ interferometer has been realized experimentally. Here we demonstrate three-photon interference that does not originate from two-photon or single photon interference. We observe phase-dependent variation of three-photon coincidences with 90.5 \pm 5.0 % visibility in a generalized Franson interferometer using energy-time entangled photon triplets. The demonstration of these strong correlations in an interferometric setting provides new avenues for multiphoton interferometry, fundamental tests of quantum mechanics and quantum information applications in higher dimensions.