Testing higher-order quantum interference with many-particle states

TL;DR

This paper experimentally investigates many-particle quantum interference beyond the second order, revealing nonzero higher-order effects and establishing bounds on fifth-order interference using a two-photon-five-slit setup.

Contribution

It demonstrates the first experimental observation of higher-order many-particle interference and sets new limits on fifth-order quantum interference.

Findings

Observed nonzero two-particle interference up to fourth order

Quantified fifth-order interference restrictions in different regimes

Provided novel bounds on higher-order quantum interference

Abstract

Quantum theory permits interference between indistinguishable paths but, at the same time, restricts its order. Single-particle interference, for instance, is limited to the second order, that is, to pairs of single-particle paths. To date, all experimental efforts to search for higher-order interferences beyond those compatible with quantum mechanics have been based on such single-particle schemes. However, quantum physics is not bounded to single-particle interference. We here experimentally study many-particle higher-order interference using a two-photon-five-slit setup. We observe nonzero two-particle interference up to fourth order, corresponding to the interference of two distinct two-particle paths. We further show that fifth-order interference is restricted to $10^{-3}$ in the intensity-correlation regime and to $10^{-2}$ in the photon-correlation regime, thus providing novel bounds on higher-order quantum interference.