Multi-photon quantum interference in a multi-port integrated photonic device

TL;DR

This paper demonstrates three-photon quantum interference in a complex integrated photonic device with multiple interferometers and modes, advancing the scalability of quantum photonic circuits for information processing.

Contribution

It introduces the first on-chip nonclassical interference with more than two inputs and a new verification scheme for multiphoton quantum behavior.

Findings

Successful three-photon interference in a multi-port device

Accurate prediction of quantum behavior using classical device characterization

Operation inconsistent with classical and bi-separable quantum models

Abstract

Increasing the complexity of quantum photonic devices is essential for many optical information processing applications to reach a regime beyond what can be classically simulated, and integrated photonics has emerged as a leading platform for achieving this. Here, we demonstrate three-photon quantum operation of an integrated device containing three coupled interferometers, eight spatial modes and many classical and nonclassical interferences. This represents a critical advance over previous complexities and the first on-chip nonclassical interference with more than two photonic inputs. We introduce a new scheme to verify quantum behaviour, using classically characterised device elements and hierarchies of photon correlation functions. We accurately predict the device's quantum behaviour and show operation inconsistent with both classical and bi-separable quantum models. Such methods for verifying multiphoton quantum behaviour are vital for achieving increased circuit complexity. Our experiment paves the way for the next generation of integrated photonic quantum simulation and computing devices.