Below-threshold error reduction in single photons through photon distillation

TL;DR

This paper demonstrates a scalable photon distillation method that reduces indistinguishability errors in photonic quantum computers, offering a resource-efficient alternative to quantum error correction for fault-tolerant quantum computing.

Contribution

The authors experimentally implement and validate photon distillation as an efficient, coherent error mitigation technique that surpasses quantum error correction in reducing errors in photonic quantum systems.

Findings

Unconditional error reduction below the fault-tolerance threshold.

Photon distillation achieves higher efficiency and threshold than quantum error correction.

Net-gain error mitigation demonstrated under realistic noise conditions.

Abstract

Photonic quantum computers use the bosonic statistics of photons to construct, through quantum interference, the large entangled states required for measurement-based quantum computation. Therefore, any which-way information present in the photons will degrade quantum interference and introduce errors. While quantum error correction can address such errors in principle, it is highly resource-intensive and operates with a low error threshold, requiring numerous high-quality optical components. We experimentally demonstrate scalable, optimal photon distillation as a substantially more resource-efficient strategy to reduce indistinguishability errors in a way that is compatible with fault-tolerant operation. Photon distillation is an intrinsically bosonic, coherent error-mitigation technique which exploits quantum interference to project single photons into purified internal states, thereby reducing indistinguishability errors at both a higher efficiency and higher threshold than quantum error correction. We observe unconditional error reduction (i.e., below-threshold behaviour) consistent with theoretical predictions, even when accounting for noise introduced by the distillation gate, thereby achieving actual net-gain error mitigation under conditions relevant for fault-tolerant quantum computing. We anticipate photon distillation will find uses in large-scale quantum computers. We also expect this work to inspire the search for additional intrinsically bosonic error-reduction strategies, even for fault-tolerant architectures.