Efficient heralding of O-band passively spatial-multiplexed photons for noise-tolerant quantum key distribution

TL;DR

This paper presents a high-efficiency heralded photon source with spatial multiplexing to improve noise rejection in O-band quantum key distribution over optical fibers, enhancing secure key rates in noisy environments.

Contribution

It introduces a passively spatial-multiplexed heralded photon source achieving 74.5% efficiency and a 37% increase in heralding rate, addressing deadtime limitations of detectors.

Findings

Heralding efficiency reached 74.5%.

Heralding rate increased by 37% with multiplexing.

Quantum bit-error rate was effectively managed over 10 km of noisy fiber.

Abstract

When implementing O-band quantum key distribution on optical fiber transmission lines carrying C-band data traffic, noise photons that arise from spontaneous Raman scattering or insufficient filtering of the classical data channels could cause the quantum bit-error rate to exceed the security threshold. In this case, a photon heralding scheme may be used to reject the uncorrelated noise photons in order to restore the quantum bit-error rate to a low level. However, the secure key rate would suffer unless one uses a heralded photon source with sufficiently high heralding rate and heralding efficiency. In this work we demonstrate a heralded photon source that has a heralding efficiency that is as high as 74.5%. One disadvantage of a typical heralded photon source is that the long deadtime of the heralding detector results in a significant drop in the heralding rate. To counter this problem, we propose a passively spatial-multiplexed configuration at the heralding arm. Using two heralding detectors in this configuration, we obtain an increase in the heralding rate by 37% and a corresponding increase in the heralded photon detection rate by 16%. We transmitted the O-band photons over 10 km of noisy optical fiber to observe the relation between quantum bit-error rate and noise-degraded second-order correlation function of the transmitted photons. The effects of afterpulsing when we shorten the deadtime of the heralding detectors are also observed and discussed.