Practical Research Of Measurement-Device-Independent Quantum Key Distribution

In today's Information Society,it can never be too overrated to talk about the im-portance of information security,which is highly relevant to our daily concerns ranging from personal privacy to national security.Therefore,how to preserve the secrecy of the information during storage and transmission becomes an appealing and interesting topic in the present.As one of the most important branches of the information secu-rity,cryptography has been studied and applied even thousands years ago.However,its history to be researched as a kind of serious science only lasts decades.During the middle years of the last century,C.E.Shannon proposed the famous Information Entropy Theory,and provided a specific method to evaluate the quantity of information.Besides,he involved information entropy theory in the field of cryp-tography,and accordingly developed cryptography from a sense of designing art into a quantitative science,opened a new chapter of the modern theory of cryptography.However,the most widely used public-key cryptographic schemes are based on complex mathematical problems,whose security have not been totally proven.Fur-thennore,due to the rapid development of the quantum computation field,the security of mathematical cryptography has been further threatened.In 1984,C.H.Bennet and G.Brassard proposed the first and the most famous quantum key distribution(QKD)scheme,BB84 protocol.The basic principles of quantum key distribution are provided by laws of quantum physics,where legitimate parties can detect the existence of eaves-dropper and thus distill the final secret keys.Together with the One-Time-Pad scheme,quantum key distribution can provide a secure communication system with absolute security.Comparing to mathematical cryptography methods,quantum key distribution pro-tocols are based on physical systems.Hence the "absolute security" are highly related to realistic factors such as imperfection of the devices and errors of the preparation as well as the detection process.In this thesis,we mainly discuss the practical security of quantum key distribution,influences of imperfect device,and true random number generation.Specifically,this thesis focuses on several topics:1.We realize the phase reference free measurement-device-independent quantum key distribution(MDI QKD)system.In this experimental system,all of the at-tacks focusing on the measurement part will be neglected.Moreover,the refer-ence frame aligning process has been removed in our system,which is a necessity in previous demonstrations.This will fundamentally reduce the requirements of the whole system,avoids the extra consumption of resources and potential secu-rity flaws of MDI QKD.2.We propose and realize a robust reference-frame-independent MDI QKD system,which eliminates the calibration of primary reference frames of the MDI system,including the phase shift of encoding quantum states and the channel polarization variation.This makes our system stable against volatile field disturbances,and further improves the practicability of MDI QKD.3.We realize an experimental MDI QKD system with uncharacterized encoding.By using the mismatched-basis statistics,we only require restrictions that the encoded states are constrained in a two-dimensional Hilbert Space,and legitimate parties are resistant to state preparation flaws even if they have no idea about the detailed information of their encoding states.4.We analyze the influences of realistic device imperfections on the Hong-Ou-Mandel(HOM)visibility,which is the core part the the MDI QKD and greatly indicates the performance of the system.In particular,we discuss the afterpulse effect with a non-Markovian model,and point out that the afterpulse effect in practical situation has a greater impact on the HOM performance than other im-perfections.5.We propose and demonstrate a true random number generation scheme.Using an effective extractor with simple time-bin encoding,the avalanche pulses of avalanche photodiode are converted into robust and high-quality random bit se-quences directly without post-processing.A light source is compatible but not necessary in our scheme,and it is promising for integrated arrays for higher speed generation.