Reexamination of the decoy-state quantum key distribution with an unstable source
Jiazhong Hu, Xiang‐Bin Wang · Physical Review A · 2010
We present an improved formula for the lower bound of the fraction of single-photon counts in a decoy-state protocol with an unstable source. Based on the formula, we study two-intensity protocol and three-intensity protocol. The major formula in the passive two-intensity protocol proposed by Adachi, Yamamoto, Koashi, and Imoto (AYKI) [Phys. Rev. Lett. 99, 180503 (2007)] actually always holds with whatever intensity fluctuation of pump light. Therefore, the protocol can always work securely without monitoring the source state or switching the source intensity. We also show that our result can greatly improve the key rate of the three-intensity protocol with a fluctuating coherent-state source.