High-dimensional Measurement-device-independent Quantum Secure Direct Communication

With digital times approaching,the importance of data security increases rapidly.In classic communication,the security of data is mainly guaranteed by the computational complexity of some mathematical problems.However,with the development of quantum algorithms and quantum computers,these classic encryption algorithms are no longer difficult to crack.Fortunately,based on the laws of quantum mechanics,quantum communication can provide data with unconditional security.Once it came out,it has attracted widespread attention at home and abroad.After decades of rapid development,quantum communication has possessed many sub-fields,quantum key distribution and quantum secret sharing,to name a few.Quantum secure direct communication is an important branch of quantum communication.This type of schemes don't need to prepare keys in advance,and can directly transmit information in the quantum channel by qubit encoded with information.While simplifying the communication process,it can still guarantee the unconditional security of secret information,and has good application prospects.Recently,quantum secure direct communication develops rapidly in both theory and experiment.The factors that limit its practical application mainly now are channel capacity and channel loss.This Master's thesis is dedicated to conducting research on these key issues then designs a high-dimensional measurement device-independent quantum secure direct communication scheme which achieves an effective enhancement of coding rate.In this scheme,the secret information is encoded on the spatial mode of the photons,expanding the dimension of coding Hilbert space from two to N,which improves the efficiency of photon information,enhances the noise tolerance,and finally realizes the increase of the coding rate.On the other hand,in order to increase the communication distance and make the designed quantum communication scheme more achievable under current technical conditions,this thesis applies measurement device-independent technique to quantum secure direct communication,which achieves the aforementioned purpose while also enhances the practical security of the protocol.For the sake of showing the performance of the protocol intuitively,we use MATLAB to simulate the process of the protocol with taking into account realistic influencing factors,then discuss and analyze the simulation results.