Experimental Research On The Technology Of Quantum Key Distribution

Based on quantum mechanics,quantum technology will change the development of computation and communication by using photons as information carriers and different information processing methods.Quantum computer has significant progress in computing power,which may lead to the collapse of the current public key cryptosystem based on mathematical complexity.Therefore,quantum key distribution(QKD)proposes a new solution to resist such crisis in the quantum era and provide a theoretical and unconditional secure cryptography method at the physical level.However,the gap between theory and imperfect devices not only brings the risk of being eavesdropped on and attacked but also reduces the QKD system’s performance.Aimed at these vulnerabilities,many protocols are put forward,thereby promoting the pace of QKD application.In this decade,with the promotion of national investment and profit of QKD commercialization.QKD has become the most practical research direction in quantum technology and has been widely applied in fibre,free-space channels as well as integrated photonics chips.Therefore,it is of great significance to deepen the experimental research of QKD protocol in a real-world environment.This paper summarizes the main works in the field of practical and proof-of-principle QKD experiments during my years of doctoral study:(1)Reference frame independent(RFI)quantum key distribution can provide a stable secure key rate in the case of difficulty in eliminating phase drift.However,the original RFI-QKD protocol does not consider the influence of source flaws.Therefore,the loss-tolerant(LT)protocol is proposed to tolerate the existence of source flaws and evaluate the secure code rate of the QKD system more accurately and rigorously.In chapter 2 of the thesis,the loss-tolerant RFI-QKD protocol is demonstrated by a time-bin phase coding system of the fibre system where source defects are quantified.The electric control system is self-built by the Lab VIEW FPGA(field-programmable gate array)instrument.The experimental key rate is also obtained in consideration of the finite-key effect.(2)Measurement device independent(MDI)protocol can eliminate the possibility of attacks on the detector site.Meanwhile,its structure with the relay extends the transmission distance limitations of the original QKD protocol.MDI-QKD will be an effective candidate for future quantum cryptography networks.In Chapter 3 of this thesis,based on the time-bin phase coding scheme,the loss-tolerant protocol is developed to the RFI-MDI-QKD protocol.By numerical simulation,the joint influence of source flaws and reference frame drift on the key rate of MDI-QKD protocol is investigated,which will benefit the research of the adaptability of MDI-QKD to imperfect devices in practical application.(3)The rapid development of waveguide devices based on various substrate material characteristics bring the optical system into the era of sophistication,integration and miniaturization.The integrated photonics chip can resist environmental noise with higher robustness and modulate photons with higher fidelity,which owns profound advantages and vast prospects in quantum technology application.In recent years,on-chip integration has become competitive research and experimental hotspot in the field of QKD.Chapter 4 of this thesis introduces an all-optical device integrated MDI-QKD transmitter chip based on indium phosphorus(InP)substrate.The fabrication of individual integrated components is packaged by Fraunhofer Heinrich-Hertz-Institute(HHI)in the form of a module library,which enables the chip designer to fulfil their anticipated function more flexibly and reliably.The design of the highspeed printed circuit board(PCB)to drive a photonics chip and parts of test work results are presented after the description of each integrated device module involved in chip design.(4)Free-space quantum key distribution in the ground-to-satellite channels or between mobile sites is essential to the global quantum communication network.However,the uncertainty of the relative motion between the transmitter and receiver and the instability of the free space channel increase the impact of the reference frame drift on the QKD system.Chapter 5 of this thesis illustrates the experimental time-bin phase encoded RFI-QKD system through a free space channel in the urban environment background.The clock signal is synchronized through a 2km free-space link between two sites located at tall buildings while quantum states are randomly prepared and sent.The result shows a quantum bit error rate as low as 1%and the C value keeps stable at around 1.5,which verified the advantages and feasibility of the RFI-QKD protocol in the free space channel.