Exponential improvement in benchmarking multiphoton interference

TL;DR

This paper introduces a scalable quantum benchmarking protocol for multi-photon indistinguishability using the quantum Fourier transform, achieving exponential improvements in efficiency and validated on a photonic quantum processor.

Contribution

The authors develop a new protocol leveraging QFT that significantly reduces sample complexity for multi-photon indistinguishability benchmarking, applicable to current photonic hardware.

Findings

Achieves constant sample complexity for prime photon numbers.

Demonstrates exponential improvement over previous methods.

Validated experimentally on a photonic quantum processor.

Abstract

Several photonic quantum technologies rely on the ability to generate multiple indistinguishable photons. Benchmarking the level of indistinguishability of these photons is essential for scalability. The Hong-Ou-Mandel dip provides a benchmark for the indistinguishability between two photons, and extending this test to the multi-photon setting has so far resulted in a protocol that computes the genuine n-photon indistinguishability (GI). However, this protocol has a sample complexity that increases exponentially with the number of input photons for an estimation of GI up to a given additive error. To address this problem, we introduce new theorems that strengthen our understanding of the relationship between distinguishability and the suppression laws of the quantum Fourier transform interferometer (QFT). Building on this, we propose a protocol using the QFT for benchmarking GI that achieves constant sample complexity for the estimation of GI up to a given additive error for prime photon numbers, and sub-polynomial scaling otherwise, representing an exponential improvement over the state of the art. We prove the optimality of our protocol in many relevant scenarios and validate our approach experimentally on Quandela's reconfigurable photonic quantum processor, where we observe a clear advantage in runtime and precision over the state of the art. We therefore establish the first scalable method for computing multi-photon indistinguishability, which applies naturally to current and near-term photonic quantum hardware.