Quantum key distribution (QKD) could help to share a secure key between two distant peers. In recent years, twin-field (TF) QKD has been widely investigated because of its long transmission distance. One of the popular variants of TF QKD is sending-or-not-sending (SNS) QKD, which has been experimentally verified to realize 1000-km level fiber key distribution. In this article, we introduce phase postselection into the SNS protocol. With this modification, the probability of selecting ``sending'' can be substantially improved. The numerical simulation shows that the transmission distance can be improved both with and without the actively odd-parity pairing method. The case of discrete phase randomization is also analyzed, a similar improvement on distance can be seen.
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Shan et al. (2024) studied this question.
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