Ambiguous discrimination among linearly dependent quantum states and its application to two-way deterministic quantum key distribution
Hua Lu · Journal of the Optical Society of America B · 2019
It is impossible to distinguish a set of linearly dependent quantum states, which ensures the security of quantum key distribution (QKD). When considering some features such as symmetry, one may distinguish a part of the quantum states from another part, called ambiguous discrimination. In this paper, we demonstrate that two-way deterministic QKD (TDQKD) is immune to photon-number-splitting (PNS) attacks for two-photon signals. When there are three or more photons in signals, the eavesdropper can gain the key bits probabilistically, without introducing any error rate. When the average number of photons per pulse takes the value of 0.1, the successful probability of PNS attacks on nonempty pulses is about 0.001, and the corresponding channel loss is about 30 dB. Our results show that TDQKD is robust against PNS attacks.