Design And Experimental Demonstration Of Practical Quantum Key Distribution Scheme

As an important technology in the field of quantum cryptography,quantum key distribution(QKD)provides a new way to ensure information security.Based on the laws of quantum physics,QKD allows to share secret keys between two legitimate communicating parties(Alice and Bob)at certain distance even under existence of an eavesdropper,Eve.Since the first BB84 protocol was proposed by Bennett and Brassard,many significant progresses have been achieved in theory and experiment,which has promote the practical process of QKD.In the practical process,it is still the focus of QKD research that how to improve the security of QKD system network,reduce the complexity of the system,and solve a series of problems.This dissertation summarizes my major research results with the proposal of improving the performance and security of the decoy BB84 QKD.The major results are outlined as follows:1.According to the random number consumption in conventional three-intensity decoy-state proposal,we employ a simple decoy-state scheme with biased basis choices where the decoy pulses are only prepared in X basis.Through this way,it can save random numbers,further simplify the electronic control system and increase key generation rate and transmission distance.Therefore,we build a quantum key distribution system with a transmission distance of more than 280 km based on phase-coding scheme to carry out corresponding proof-of-principle demonstration.Taking the finite-size key effects into account,we adopt the global optimization scheme,which greatly improves the key rate.By incorporating with low-loss asymmetric Mach-Zehnder(MZ)interferometers and superconducting single-photon detectors,we can obtain a secret key rate of 3.33 × 10-5bit per pulse at 201 km and 3.89 × 10-7bit per pulse at 280 km coiled optical fibers,respectively.2.Taking the state preparation flaws due to the imperfections of real-life implementations into consideration,we employ the BB84 quantum key distribution system to realize an experimental decoy-state QKD demonstration with uncharacterized encoding sources and projective measurements by incorporating the mismatched-basis data,which only requires that the encoding states are two-dimensional.Furthermore,the measurement operation of the receiver is loosened to be projective measurements.The experimental setting of our demonstration is just the same as the BB84 QKD systems,but endows a higher practical security level,which relaxes the assumption of device dependence in some sense.Finally,with a rigorous statistical fluctuation analysis,we can distribute secret keys when the transmission distances of the standard fiber link are 101 and 202 km.3.The decoy state scheme is the most widely used method to detect existence of eavesdropping in quantum key distribution system.A rigorous statistical fluctuation analysis is required against general attacks in the finite-key regime.Statistical fluctuation analysis methods are very important in dealing with finite-key effects,which directly affect secret key rate,secure transmission distance and even the most important security.We use several commonly used statistical fluctuation analysis methods to estimate the deviation between expected value and observed value for a given expected value or observed and compare the differences between these statistical fluctuations.This work will provide a reference for the selection of statistical fluctuation methods about the finite-key effects in the future.