Improved statistical fluctuation analysis for twin-field quantum key distribution

The decoy state scheme is the most widely studied quantum key distribution protocol to detect existence of eavesdropping. Twin-field quantum key distribution (TF-QKD) is a promising protocol for realizing secret key sharing over long distances. However, the secret key rate becomes relatively low considering the finite-size effect. In this study, the statistical fluctuation analysis of the four-intensity decoy-state TF-QKD system proposed in a recent study (Zhang et al. in Phys Rev A 95:012333, 2017) is considered, and its performance is compared with the results of the Gaussian approximation and Chernoff bound methods. Numerical simulations show that the suggested method shows a considerable improvement in both the key generation rate and transmission distance over the Chernoff bound method under actual experimental environment. We find that the scheme increases secret key rate 1.04-4.06 times and transmission distances 10-18 km farther. We also present optimized parameters for Gaussian, Chernoff, and our scheme.