Research On Practical Quantum Secure Communication

With the rapid development of information technology,information security has become more and more important.Based on quantum mechanics,quantum secure communication provides a new technology for secure communication.Quantum secure communication includes major modes such as quantum key distribution and quantum secure direct communication.This doctoral thesis focuses on the study of practical quantum secure communication,which mainly involves two aspects,namely the systematically study of practical quantum secure direct communication,and the design and implementation of two-way self-stabilizing quantum key distribution.Quantum secure direct communication can transmit information directly in quantum channel,which has changed the mechanism of two separate transmissions of encryption and communication into a single transmission mechanism,which is a new security communication framework.Based on the principle that unknown quantum states cannot be measured without disturbing the system and leaving traces,quantum secure direct communication can estimate the security capacity required in the physical layer security theory.For practical quantum secure direct communication,it faces with the challenge of ensuring both the reliability and security of information and the unavailability of practical quantum memory under the existing technology conditions.In view of the these problems,we develop the original protocol based on the theory of wire-tap channel,and completes the quantitative security analysis under the condition of collective attack.We have designed a specific communication scheme and set up the demonstration that achieves secure and reliable communication with a transmission rate of 50 bps,in 1.5 km fibre.To solve problem of quantum storage,we propose a chain block coding scheme,which links the security of multiple blocks of data and realizes quantum secure direct communication without quantum storage.This work has solved one big obstacle of the practical application of quantum secure direct communication,and pushed forward its development.In quantum secure communication,eavesdroppers are assumed to have unlimited capability that does not violate the principle of quantum mechanics.Noise is unavoidable in the actual environment,and eavesdroppers can hide the interference she introduces in these noises.Therefore,noise suppression is one of the most important tasks for practical quantum secure communication.Noises in optical fibre systems mainly come from factors such as pressure,vibration and temperature of the environment,which cause optical interference instability.The two-way structure can automatically compensate the birefringence and phase drift in optical fibre by magnetic-optic effect,and eliminates almost completely the optical interference instability they cause.This greatly improves the stability of transmission.However,the two-way transmission structure gives eavesdroppers more strategy,such as Trojan attacks.Based on the security analysis of the two-way structure,we optimize the two-way quantum communication protocol,put forward a protocol without active compensation,and quantitatively analysis its security under the condition of collective attack.The information carrier is protected by the automatic compensation mechanism of the two-way structure,and the quantum states that are highly robust to noise are used for the estimation of the phase error.We have experimentally demonstrated the two-way quantum key distribution,which is high fidelity for a long time in a 50 km of commercial fibre.The design can not only keep the long-time stability and robustness of information transmission,but also maintain the plug-and-play feature,which has the prospect of wide applications.