A Theoretical Research On Unidimensional Continuous Variable Quantum Key Distribution

With developments in science and technology and an improved global communication network,information exchange has become increasingly convenient,leading to increased focus on security of information.Information security affects our daily life,business confidentiality,military operations,and national politics.Secure communication between two parties can be achieved using techniques based on the fundamental principles of quantum physics: legitimate communication parties can obtain a set of unconditionally secure random keys to encrypt and decrypt information,and any third-party eavesdroppers can be discovered by the legitimate users.The unconditional security offered by such quantum key distribution(QKD)protocols has received global government and research attention,resulting in rapid developments with inestimable value in the fields of defense,commerce,and communication.The first QKD protocol was Bennett and Brassard's BB84 protocol.Since then,several countries have paid increasing attention to QKD technology,leading to rapid developments in relevant theoretical and experimental research.At present,QKD protocols generally fall into one of two categories: discrete variable quantum key distribution(DVQKD)protocols such as BB84,and E91,and continuous variable quantum key distribution(CVQKD)protocols such as GG02,and the four-state discrete modulation protocol.CVQKD is one of the most popular protocols for research owing to its simple source preparation,reliance on low-cost high-efficiency measurement equipment,and its compatibility with current optical communication networks.In the current research,it is important to improve or simplify the system protocol and develop the key technology.In particular,unidimensional(UD)CVQKD has been widely researched because of its simple modulation process,low cost,and low consumption of random numbers,resulting from its use of a single modulator to encode information.In two-dimensional protocol,when the degree of squeeze is high,the performance of the squeezed state protocol is better than that of the coherent state protocol,and the UD protocol is limited to the coherent state at present.Therefore,this paper extends the UD coherent state to the squeezed state for research,and compares the performance of the UD coherent state to that of the squeezed state.In addition to the improvement of the protocol,we also pay attention to the influence of the change of the polarization state of the optical channel on the system channel parameters in CVQKD,which provides a basis for us to analyze the security of system.This research contents of this paper are:1.In this study,we propose CVQKD with a UD squeezed state,and establish a uniform covariance matrix for UD coherent and squeezed states.In addition,equivalence between the prepare-and-measure(PM)scheme and entanglement-based(EB)scheme is proved.We analyze the security of direct reconciliation(DR)and reverse reconciliation(RR)UD coherent and squeezed state protocols under collective attack,and compare the performance of both protocols with DR and RR.Numerical simulation results show that the performance of the UD amplitude squeezed state is not as good as that of the coherent state with DR or RR.However,the performance of the UD phase squeezed state is better than that of the coherent state with RR over long distances,but its space of promotion is very little.The UD phase squeezed state performs better with DR than RR,however,the transmission distance is limited.Considering that the coherent state protocol is easier to prepare than the squeezed state,and the squeezing effect of the latter does not significantly improve protocol performance,the UD coherent state protocol offers greater practical advantages.2.In CVQKD with Gaussian-modulated coherent states,the polarization states of signal and local light sources during transmission are shifted owing to single-mode fiber birefringence.The polarization extinction ratio of signal light and local light is usually reduced subsequent to polarization demultiplexing,which has a significant effect on the relative phase locking of local and signal light in the receiver,and on the results of balanced homodyne detection.And then this affects the performance of the system.It is therefore particularly important to study the influence of variation in polarization lock and extinction ratio on the system channel parameters.In this study,we present simulation results demonstrating the influence of the polarization extinction ratio on channel parameters.3.To help students understand leading scientific research and to enrich our experimental teaching content,we developed a polarization control and measurement instrument with the following functions: first,it can measure the Stokes vector of the polarization state using optical devices including a wave plate and electric rotating table;second,it can demonstrate the polarization locking process using a dynamic polarization controller and tricyclic polarization controller.