Enhanced Analysis for the Decoy‐State Method

Quantum key distribution stands as a cornerstone of quantum information science, enabling secure communication based on fundamental quantum principles. In reality, practical implementations often rely on the decoy‐state method to ensure security against photon‐number‐splitting attacks. A significant challenge in realistic quantum cryptosystems arises from statistical fluctuations due to finite data sizes, which complicate the key‐rate estimation because of the nonlinear dependence on the phase error rate. In this study, the key rate bound for the decoy‐state method is refined and enhanced and introduce an improved statistical fluctuation analysis framework. By integrating the refined bound with this advanced fluctuation analysis, higher key generation rates are achieved, as demonstrated in numerical simulations of the one‐decoy‐state method — a simple yet increasingly practical protocol — under typical experimental conditions. Notably, the approach to fluctuation analysis extends beyond quantum cryptography, offering broad applicability to various quantum information processing tasks, particularly those involving linear relationships between objectives and experimental variables.