Practical Research Of Quantum Key Distribution

For thousands of years,kings,queens and generals have relied in efficient commu-nication in order to govern their counties and command their armies.At the same time,they have all been aware of the consequences of their messages falling into opposing forces,then all kinds of secure communication ways have been created.Accompany with the coming of the information era,secure communication begin to effect every aspect of our life,and becomes more and more important.Commercial ciphers can be divided into two parts:Symmetrical cryptography and Asymmetrical cryptography.For the former,the key point is how to share the same keys between two parities in communication without be known by the eavesdropper.And for the latter,its security lies in the computational complexity of its correspond mathematical model,which proves that the reverse calculation of a mathematical prob-lem is complex enough that its computational time is much greater than the service life of the encrypted information.But the security of these two kinds of ciphers is facing unprecedented challenges because of the advent of quantum computing era.Quantum cryptography is a cross technology combining with quantum mechanics and cryptography,Its security is ensured by the laws of physics rather than unproven mathematical complexity.Any third party eavesdropping in the process of key trans-mission between the two parties of the communication will be perceived.Then com-bined with 'One Time Pad' cipher,the absolute security of quantum cryptography can be proven.Because of this unique advantage,quantum cryptography becomes the most promising secure communication way in the quantum computing era.This article mainly summarizes the author's relevant research and achievements related to the practical use of quantum key distribution technology during the doctoral period,including the following aspects:1,Optical fiber has become one of the typical channels of quantum key systems because of its stability,easy scalability and low loss.However,for most quantum key systems,the polarization change caused by the birefringence effect of the fiber will cause the bit error rate to increase,which will reduce the system efficiency.For the external field fiber,due to the complex environment,the effect of birefringence will be more serious.Therefore,we conduct on-site measurement of a quantum wide-area network and an aerial cable.Then we proposed one high-efficiency analysis method to analyze and summarize the measurement results.The analysis results can be used as an important reference for the quantum key systems which working in the field fiber network.2,For polarization-sensitive quantum key distribution systems,polarization vari-ations in the channel can cause the rise of bit error rate,which reducing system effi-ciency.Therefore,an efficient polarization reference alignment system is particularly important.We propose an efficient and simple reference alignment method which uses only the redundant information generated during the operation of the quantum key dis-tribution systems,and in combination with a squeeze polarization controller,the method perform efficient compensation to the polarization variations in the channel.And we have verified its feasibility through experiments.3,Different from characters and text information,multimedia information such as images and videos is a type of information with high sparseness.If we directly use quantum key distribution technology and 'one time pad' cipher to encrypt multimedia information,due to the low key rate of quantum key distribution systems,the transmis-sion bandwidth will be insufficient.Combining with the compressed sensing method,we propose a high-bandwidth secure transmission method of multimedia information.With this method,on the one hand,the key consumed when encrypting the unit multi-media information is reduced,and at the same time,the computational security of the multimedia information transmission is ensured.On the other hand,the intensity of error correction and the secrecy amplification can be reduced appropriately,thereby in-creasing the available key generation rate of the quantum key distribution system.We verified the effectiveness of the method through experiments.