Quantum Key Distribution Protocol With Multiple Degrees Of Freedom Or Non-ideal Light Sources

Quantum cryptography,which is based on quantum physics,uses quantum information technology to establish a secure key between the two sides of communication,and uses the key to protect the communication data to achieve the secure communication.Hence it has a higher security,which has attracted great attention in cryptography,and is considered to be a kind of secure communication with great potential in the future.Quantum key distribution(QKD),as a key technology of quantum cryptography,is an important research direction.It is also the first practical direction in the field of quantum secure communication.QKD is based on the uncertainty principle and quantum non-cloning theorem in quantum mechanics.It takes quantum state as information carrier,uses quantum information technology to establish absolutely secure keys between the two parties of communication,and then uses the keys to protect communication data.It overcomes the security risks of the classic encryption technology,and it is a key distribution technology that has been rigorously proven to guarantee unconditional security in principle.In order to improve the security and the performance of the QKD protocol,various QKD protocols and improvement protocols have been proposed.However,due to the limitations of actual physical devices,such as actual light source devices,detection devices,and transmission channels,the performance of the current QKD system is limited,and it is still difficult to meet the current high-speed growing requirements of long-distance data communication,especially to the one-time encryption requirements.In the thesis,based on the study of the information coding in multiple degrees of freedom and the non-ideal light sources adopted in practice,four improved QKD protocols are proposed.The main contents and innovations of the thesis are as follows:(1)A measurement-device-independent quantum key distribution protocol based on pulse position modulation is proposed.In view of the characteristics and problems of weak coherent light source,which is commonly adopted in most of QKD protocols,the pulse position modulation(PPM)technique is introduced into data post-processing process of the measurement-device-independent quantum key distribution(MDI-QKD)protocol,and it is named as PPM-MDI-QKD protocol.Combining some empty pulses with a single photon pulse,the protocol makes full use of the pulses from the weak source,and achieves high-dimensional encoding by using the position of the single photon pulse.Hence the protocol enhances the performance of QKD.(2)A quantum key distribution protocol based on polarization-phase degrees of freedom is proposed.Any quantum can have a mixed quantum state in multiple degrees of freedom,which can be obtained and distinguished physically.Introducing the feature into the QKD,a quantum key distribution protocol based on hybrid quantum state in multiple degrees of freedom is proposed.In our protocol,the quantum states in two degrees of freedom of polarization and phase are selected,which are often used in quantum communication.By using the characteristics of round robin differential phase shift quantum key distribution(RRDPS-QKD),polarization coding and round robin differential phase shift coding are combined to establish a two-bit QKD.The protocol can improve the key rate of the system by using hybrid coding in a variety of degrees of freedom,and the amount of information carried by photons in the system breaks through the limitation of single-degree-of-freedom single-bit signals.(3)A plug-and-play round-robin differential phase shift quantum key distribution protocol is proposed.In the implementation of QKD,the fluctuation of the intensity of the light source,the influence of the environment and the birefringence effect of the transmitted light destroy the assumption of the trusted source.Moreover,these factors have a nonnegligible effect on QKD system.Therefore,a more practical plug-and-play RRDPS-QKD protocol is proposed in the thesis.The protocol can self-compensate the birefringence effect of the channel through two-way transmission,and can establish a RRDPS protocol even with an untrusted source.So the protocol is more practical.(4)The decoyed states round-robin differential phase shift quantum key distribution protocol with source errors is studied.In the actual implementation of quantum key distribution,the influence of fluctuation of the sources in QKD can not be ignored.Therefore,the performance of RRDPS-QKD protocol with light source errors is studied.In this thesis,adopting three decoy states method,the formula of count rates based on the fluctuation parameters of the light source errors is deduced,and the key generation rate of the prototol is lower bounded.The content of this study makes the performance of the system more realistic.