Research On Measurement-device-independent Quantum Secure Direct Communication

Confidential communication is indispensable to modern society.Quantum communication provides a distinct new way for that,whose security is ensured by quantum principles.There are two kinds of manners in quantum communication,which are quantum key distribution and quantum secure direct communication(QSDC).The quantum key distribution can make two legal users share a key securely through the key agreement,and the quantum communication is completed by combining classical encryption-decryption channel.QSDC can transmit secure information directly in quantum channel without distributing secure key in advance,hence achieve the quantum communication.Along with the development of theoretical research,prove-of-principle experiments of entanglement based two-step QSDC and single photon based DL04 protocol have been achieved in the optical fiber system and quantum memory optical platform since the first QSDC protocol was proposed,and the full function QSDC prototype has also been completed.Measurement devices in the practical quantum communication system have defects that can lead to security loopholes,and threaten the security of practical quantum communication systems.In the practical application of QSDC,security threat from imperfect measurement devices is unavoidable,and demands prompt solutions.In order to solve the problem of security loopholes that originate from defects of measurement devices in the practical QSDC system,considering the features of QSDC,a measurement-device-independent quantum secure direct communication(MDI-QSDC)protocol is proposed in this thesis.It addresses the security vulnerabilities from defects of measurement devices.The major innovation achievements in this thesis including:1.An entanglement based measurement-device-independent two-step quantum secure direct communication(MDI-TS)protocol is proposed,which eliminates all loopholes related to measurement devices and all relevant side channels.It strengthens the security of practical QSDC systems,and has a high communication capacity due to dense coding.2.Security analysis of MDI-QSDC protocol is completed in this thesis.Utilizing Csiszár-Korner theory,security of two MDI-QSDC protocols,entanglement based MDITS protocol and single photon based MDI-DL04 protocol,is proven and the lower bound of secrecy capacity of each protocol is derived,respectively.Compared with QSDC,MDIQSDC has a slight decrease in secrecy capacity at the price of enhancing the security.However,MDI-QSDC can double the transmission distance of QSDC.3.An MDI quantum dialogue protocol is proposed in this thesis by generalizing MDI-TS protocol with its symmetry,and achieving a bidirectional QSDC without encryption.Besides,a key is also available through an agreement process in this protocol,and two legitimate users can decode messages simultaneously with that key.MDI quantum dialogue protocol enables bidirectional communication in practical QSDC systems,and enhances its flexibility in networking.