Performance evaluation of twin-field quantum key distribution using avalanche photodiode single-photon detectors

Twin-field quantum key distribution (TF-QKD) surpasses the repeaterless key-rate bound, offering great promise for long-distance quantum communication. Avalanche-photodiode (APD) single-photon detectors are widely used in practical QKD systems, due to their compactness, cost-effectiveness, and room-temperature operation. However, their non-ideal characteristics-including afterpulse probability, dead time, and dark counts-can severely degrade TF-QKD performance. In this work, we develop a comprehensive TF-QKD simulation model incorporating these APD imperfections, enabling quantitative analysis of their individual impacts. Our results reveal that afterpulse induced by high-intensity reference pulses is the dominant performance-limiting factor. Under identical APD conditions, we compare three representative TF-QKD protocols. The sending-or-not-sending (SNS) protocol demonstrates superior long-distance performance due to its higher signal photon number and enhanced noise tolerance. This study provides practical guidance for the design of compact, APD-based TF-QKD systems and highlights key strategies for performance optimization.