Investigation On Key Technologies Of Free-space Continuous-variable Quantum Key Distribution

Quantum cryptography exploits the fundamental quantum mechanics to achieve the remote distribution of secret key,which is developing towards solving the practical problem of constructing scalable and secure quantum network.Among them,free-space continuous-variable quantum key distribution is a kind of communication technology which uses continuous-variable quantum state to transmit secret key in free space.Because it can break the limitation of optical fiber transmission path,it becomes an important way to realize long-distance quantum network.However,the quantum states transmitted in free space will inevitably be affected by atmospheric turbulence and other effects,leading to the degradation of system performance.In this thesis,we focus on the key technologies of free-space continuous-variable quantum key distribution,aiming to establish and improve the research of parameter estimation,excess noise suppression,privacy amplification and other technologies in free space system,in order to improve and strengthen the system performance.The following research findings have been achieved in the theoretical study of free-space continuous-variable quantum key distribution:1.We propose a parameter estimation method for free-space continuous-variable quantum key distribution.On this basis,the influence of transmission fluctuation on the system performance under the actual transmission condition is studied.The results show that this method is consistent with the physical model and can effectively resist the entanglement-distillation attack.Therefore,the proposed method fills in the blanks in parameter estimation of practical free-space continuous-variable quantum key distribution.2.There exsit some problems,such as the trade-off between key rate and parameter estimation accuracy,and information leakage caused by data exchange,in traditional parameter estimation.Therefore,we propose a blind parameter estimation method for free-space continuous-variable quantum key distribution.Through simulation analysis and experimental verification,this method can not only effectively solve the problems in traditional methods,but also further reduce the impact of privacy amplification on the system,so as to effectively improve the system performance.3.We propose a free-space continuous-variable quantum key distribution scheme based on adaptive optics in order to effectively suppress the excess noise caused by channel fluctuation in quantum communication.The scheme is analyzed from physical model and optical field.The analysis shows that the proposed scheme can effectively control the excess noise and improve the system performance.Therefore,the further development and improvement of adaptive optics technology may break the distance limit caused by the excess noise due to the channel fluctuation,and lay the foundation for the construction of large-scale high-performance quantum network.4.We propose a continuous-variable quantum key distribution protocol based on quantum privacy amplification with CV Bell detection.In this protocol,CV bell detection is used to measure the quantum signal,and at the same time,it can realize the privacy amplification,and establish private correlations between the legitimate communication parties under the presence of an eavesdropper.Compared with the traditional protocol,this protocol significantly reduces the loss of the original key variables in the data processing process,thus improving the system performance.The analysis shows that the protocol can obtain a higher secret key rate and a longest propagation distance in theory,and show a good excess noise tolerance.Therefore,the protocol provides an effective way for the realization of quantum key distribution with long distance and high performance.