Afterpulse analysis for practical phase-matching quantum key distribution

Abstract

Twin-field quantum key distribution (TF-QKD) enables secure communication over high transmission losses, which can overcome the linear key-rate constraint without quantum repeaters. As an important variant of TF-QKD, phase-matching QKD (PM-QKD) has garnered considerable attention due to the advantage of preparing states in only one basis for both key generation and parameter estimation. To advance the practical deployment of PM-QKD systems, single-photon avalanche detectors (SPADs) represent a superior choice owing to their compact size, low cost, and high robustness. Nevertheless, the afterpulses inherent in SPADs can introduce unexpected avalanches, which, if omitted, will make the observables in the numerical simulation deviate from those in the actual experiment. Here, we develop an afterpulse-compatible model to address this issue. Simulation results demonstrate that the afterpulses degrade the secret key rate and transmission loss of PM-QKD. Furthermore, to alleviate the performance degradation under the afterpulse effect, we apply the advantage distillation method to enhance the key rate and tolerable transmission loss.