Optimization analysis for the maximum pairing length of mode-pairing quantum key distribution.

Mode-pairing quantum key distribution (MP-QKD) circumvents the need for phase locking through post-selection pairing, still allowing it to surpass the repeaterless rate-transmittance limit. This protocol, therefore, presents a promising approach for practical QKD implementation. Without phase locking and tracking, the performance of the laser, channel, and detector critically affects the determination of the maximum pairing length in pairing strategies. However, previous studies have typically set based on empirical data without conducting a thorough analysis. In this study, to more accurately reflect real-world conditions, we consider fiber fluctuations, laser linewidth, laser frequency offset, and after-pulse effect to quantify the systematic misalignment determined by . We employ the three-intensity decoy-state method, accounting for the finite data-size effect, to evaluate the impact of in practical scenarios. Our simulation results demonstrate significant enhancements achievable through the optimal selection of . Therefore, this study provides valuable insights for the advancement of future MP-QKD experiments and applications.