Reasearch Of The Source-side Security For The Measurement-Device-Independent Quantum Key Distribution

The information security has attracted more and more attention in the era of the information since the frequent information interaction has became a part of people’s daily life and the foundation of many important fields such as politics,economy,and military.Information security is inseparable from the development of cryptography.However,the security of the modern cryptography is seriously threatened since the rapid development of the quantum computation.In this context,a novel method named quantum key distribution(QKD)for distributing secret keys has been valued in the field of academia and industry.With the properties of the quantum mechanics such as the indivisibility of the single-photon and the quantum non-cloning theorem,QKD allows two remote users,named Alice and Bob,to distribute secret keys even if there is a eveasdropper,Eve.The security of the original QKD protocol relys on the assumption that the source side and detection side are absolutely secure and the source side must accurately modulate the quantum states.It seems that the above assumptions in the theory are reasonable.However,there are gaps between theory and pactice since the non-ideal properties of practical devices which can be utilized by Eve to hack the system without attracting any attention.The non-ideal properties of the detection side are once regarded as the most threatening loopholes owing to the fatal attacks such as the faked state attack,time shift attack,dead time attack,SPD blinding attack and so on.To deal with these troublesome attacks,a protocol named measurement-device-independent quantum key distribution(MDI-QKD)was proposed.The MDI-QKD immune to all detection-side attacks.It even allows the Eve to perform as the detection side.Due to the high performance and security,the MDI-QKD has been the regarded as one of the most promising QKD protocols.The MDI-QKD has solved the most vulnerable detection-side hoopholes.However with the in-depth study of device non-ideality,more and more source-side loopholes have been discovered and proposed.Although the protocol is immune to all detectionside attacks,the source-side attacks are still threatening.How to eliminate the sourceside loopholes while keeping a high-performance has been a troublesome problem to be solved.To bridge the gap between the theory and the practice,in this work,we promote the practical process of QKD by proposing new protocol and improving existing theoretical method against the modulation misalignment,and designing new devices and tomography method against the intensity fluctuations.Besides,we have also experimentally demonstrated the above theories.The relevant research results are summarized as follows:1:The original MDI-QKD requires the users to randomly prepare the four ideal BB84 states in the source-side.However,due to the non-ideal properties of the encoders and the various modulation errors,this requirement is difficult to meet in practice,which would increase the bit error rate and bring opportunities for Eve’s eavesdropping.In order to solve this problem,we design a special MDI-QKD protocol named misalignmenttolerant measurement-device-independent quantum key distribution,which remains security and high performance even if the modulated quantum states do not satisfy the mutual unbiased condition.Further,we also give the security proof,design a decoystate method and experimentally demonstrate its practical abilities.2:The reference-frame-independent measurement-device-independent quantum key distribution(RFI-MDI-QKD)is a special MDI-QKD protocol that is immune to the problem of the source-side reference frame drift.Although it has higher robustness and better security,the low secret key rate is still an obstacle for its development.To solve this problem,we proposed a improved RFI-MDI-QKD by introducing potential relations between different bases,which greatly improves the protocol performance.In addition,this improvement also provides a guarantee for the QKD network.Based on this improved protocol,we design an MDI-QKD network and build a system to experimentally demonstrate its practical performance.3:The twin-field quantum key distribution(TF-QKD)is a recently proposed protocol with the measurement-device-independent property.The TF-QKD is immune to all detection-side attacks,and can also reduce the channel loss from η to(?)to realize ultra-long-distance key distribution.In this work,we further improve the practical security of the protocol by giving its secret key rate in the finite-key-size regime that the data size is limited and the eavesdropper has quantum computing and quantum storage.Besides,we also analyzed some non-ideal properties of the intensity modulation at the source-side,and proposed a tomographic method to keep the high performance when the source has large random fluctuations.4:In recent years,a new source-side loophole named "patterning-effect" is presented.Due to the non-ideal electronic properties such as bandwidth limitation,thermal noise,time jitter and so on.the practically loaded voltage on the intensity modulators is not what the users want,which leads to random fluctuations of the modulated intensities and correlations between adjacent pulses.The patterning-effect breaks the important IID assumption and shakes the bases of the security proof.To deal with the loophole,we designed a new modulator that can mitigate the patterning-effect.We theoretically analyzed the modulator,and demonstrated its property by simulation and experiment.