Experimental Study On Ultra Long Distance Quantum Key Distribution

Quantum teleportation is a frontier interdiscipline and one of the research focuses that combines quantum information science and computer science.As the key direction of quantum teleportation,Quantum key distribution(QKD),based on the principle of quantum mechanics,provides theoretical solution for secure and confidential commu-nication,which has inherent advantages in physical essence over traditional commu-nication methods.Thus,QKD is very suitable for government,financial institutions,schools and other communication environments that require high security which make QKD become the important part of future network.The BB84 protocol was proposed as the world's first QKD protocol in 1984.Since then,QKD has evolved toward higher coding rates and farther secure transmission distances,and has become the most practi-cal and widely used direction in the field of quantum communication.At present,with the application of commercial QKD systems and related networks,China has success-fully tested and implement Hefei Network,Jinan Network,Quantum Beijing-Shanghai Main Line,and the'Micius' quantum experimental satellite.Meanwhile,there are still many theoretical and experimental problems that limits the practical development of QKD.BB84 type protocol,whose security based on the single photon,is very sensitive to channel loss,restrict the point-to-point communica-tion distance.Due to high requirement of two-photon interference sent by the two com-municating parties,the measurement device-independent QKD protocol(MDI-QKD)cannot gets a high rate,though it can theoretically double the communication distance and perfectly overcome the security loopholes of the detected receiver.From an ex-perimental point of view,the polarization coding method is widely used in many QKD protocols,but it is difficult to guarantee the fidelity of polarization coding after long fiber transmission.The phase coding method is robust to the environment fluctuation in long distance transmission,but the optical signal in decoding process has a loss of 3 dB.These problems have hindered the practical process of QKD,which is an urgent problem to be solved.This thesis mainly focuses on the current problems of fiber based QKD systems with higher speeds and rates,longer transmission distances,including new theoreti-cal schemes and protocols.We mainly analyze the relevant MDIQKD based theoreti-cal basis,experimental technology,system design,and experimental process.Related theoretical foundations include time-bin-phase encoding MDIQKD theory,twin-field QKD theory(TFQKD),sending or not sending QKD theory(SNSQKD),phase match-ing QKD theory(PMQKD).In terms of experiments and systems,the process of tech-nical design and system construction of the QKD system are reported in this thesis.By overcoming the phase disturbance in the ultra long distance QKD system and re-alizing the single photon interference,we complete a high-speed,high-performance,high-stability,simple-structure general QKD system suitable for related new theories,and successfully realize the experiment of PMQKD protocol.We first time achieve the world's longest distance indoor QKD experiment,breaking the limit of QKD theoretical rate.In this work,a world record for the secure transmission of quantum communica-tion is set,which greatly promotes the practical QKD,and provides technical references and technical accumulation for the construction of future quantum communication net-works.