Study Of Decoy-State Quantum Key Distribution

quantum key distribution (QKD) could well be the first application of quantum mechanics at the single-quantum level. In theory, QKD holds the key to unconditional security in communications, which make the traditional cryptography fell small. In practice, all recent long-distance implementations of QKD are fundamentally insecure, due to real-life imperfections. To bridge this big gap between theory and practice, the ideal of decoy states has recently been proposed for substantially improving the performance of QKD. A further study of decoy-state method is the main work of this paper.The paper is composed of six chapter. The first chapter is mainly aimed to introduce the history of development and latest progress in the field of QKD. The second chapter introduces the basic theories of QKD and the three most typical QKD protocols. In chapter three, we firstly model the real-life QKD setup which uses the weak coherent state as the source. We then introduce the photon-number-splitting (PNS) attack, and give the basic ideals and operations of two important methods, the decoy states and the nonorthogo-nal encoding method, which are used to combat the PNS attack. In chapter three, we firstly analyze the security issue of decoy-state BB84 protocol, then present a theorem for calculate the secure key generation rate of a nonorthog-onal encoding scheme, which are extended to the general situation. Based on this theorem, we present a specific nonorthogonal decoy-state QKD protocol followed by a security analysis. In chapter five, we further our study of the practical weak coherent sate QKD experiments, and obtain a necessary condition of practical decoy-state QKD protocols. We then propose a Signal-decoy dualpurpose QKD protocol. Finally, in chapter six, we give a concise conclusion of this paper and make an expectation of the future in this field.