Research On Quantum Key Distribution System In Terahertz Band

Quantum key distribution(QKD)has been developing rapidly in theory and experiments over the past three decades.It has been stepping into the phase of the practical application.QKD provides a way to unconditionally secure key distribution between two distant parties,which is unmatched by any security measures in classic wireless communications.However,existing QKD systems are mostly based on fiber optics and the equipment is too cumbersome and expensive,and the QKD protocol for short-range wireless communication is in urgent need of development.The Terahertz Quantum Key Distribution(THz QKD)protocol not only solves the scarcity of the wireless communication band,but also ensures the unconditional security of communication.THz QKD is one of the most promising solutions for the practical application of QKD.First of all,we briefly introduce the development of QKD,the needs of wireless communication systems and the inadequacies of existing QKD systems.The advantages of terahertz band QKD are analyzed,and the methods and techniques for implementing THz QKD protocol are discussed.Secondly,the related theoretical foundations of THz QKD protocol are introduced: quantum mechanics related theorems and information theory related foundations;quantum state modulation scheme,quantum channel modeling and receiver measurement method;security analysis model,eavesdropping attack scheme and system are discussed.we focus on the noise of the principle and process of the CV-QKD system.Thirdly,the influence of quantum state and thermal noise in the THz band is discussed.The transmission characteristics of the THz band channel and the thermal QKD protocol analysis model are analyzed.Based on this,a THz band QKD protocol is proposed.The security analysis and key rate calculations indicate that the ideal communication distance of the THz QKD system can reach 58 m.In addition,combined with the existing THz and optical devices,a possible system scheme is given,and the factors including the security key rate and the secure transmission distance are analyzed under the indoor channel model.We conclude that the scheme combined the forward information coordination and the homodyne detection is the optimal solution to implement THz QKD.Fourthly,combined with OFDM technology,a scheme to improve the key rate of THz QKD system is proposed.The working principles of each module of OFDM-based THz QKD system are discussed: OFDM coding technology,orthogonal modulation technology and homodyne measurement technology.Based on the OFDM THz QKD protocol and security analysis,it showed that the secure transmission distance of the 0.35 THz QKD system is 14 m.When the 32-channel orthogonal carrier multiplexing scheme is adopted,the key rate of the system can be increased by 31 times,while the loss of transmission distance is low.Finally,summarize the full text and look forward to the next step.