Secure communications based on sending-or-not-sending strategy

Recently, there are various schemes of quantum secure direct communications that have been studied. Most of these protocols commit themselves to accomplishing two goals: increasing the coding rate and expanding the range of quantum direct communications. Here in this study, a quantum secure communication protocol using the sending-or-not-sending strategy is proposed, which significantly enhances the communication distance. Numerical simulation results show that although the misalignment error eopt\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$e_{opt}$$\end{document} increases as large as 45%\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$45\%$$\end{document}, the protocol can still achieve a distance of approximately 350 km. Although the long-distance single-photon inference is involved in decoy windows, it is not required to use this technology in signal windows established for secret message transmission. Moreover, the security of the protocol against collective attacks is analyzed based on Wyner’s wiretap channel theory.