High-speed Chip-based Measurement-device-independent Quantum Key Distribution

Quantum communication is a field of applied quantum physics closely related to quantum information processing and quantum teleportation.Its most interesting appli-cation is protecting information channels against eavesdropping by means of quantum cryptography.The most well known and commercialized application of quantum cryp-tography is quantum key distribution(QKD).The security of QKD is guaranteed by the validity of quantum physics,which is quantum no-cloning theory-unknown quantum states can not be copied precisely.Since the proposal of BB84 protocol by Bennett and Brassard in 1984,the se-curity theory and experimental research of QKD have a huge development,including some outstanding works,such as,GLLP(Gottesman-Lo-Lutkenhaus-Preskill)frame-work,decoy-state method,measurement-device-independent QKD(MDI-QKD),the backbone network between Beijing and Shanghai,and Micius quantum satellite et.al.The problem lying in front of us is the practicality of QKD networks among which,practical security is utmost important,and how to achieve a longer distance,higher key rate,and lower cost QKD network is next.Existing QKD networks are implemented based on trusted relays.Trusted relays have the risk of being attacked or even controlled by eavesdroppers,which will bring security issues.MDI-QKD networks based on untrusted relays can solve this prob-lem.Relatively expensive and complex single-photon detectors are located at the cen-tral node,while user nodes are equipped with transmitters which can be integrated on chips by nanophotonics technology,reducing the cost of users further.As a first step,we performed a chip-based MDI-QKD experiment for two users and raised the system clock to 1.25 GHz.To this end,we have developed a high-interference visibility light source and a GHz modulation pulse generator.Besides,the transmitter(except the light source)is integrated on a silicon photonics chip.Finally,we achieve the highest key rate at the same distance among reported MDI-QKD experiments.This work not only increases the key rate by a factor of 6,but also lays the foundation for future chip-based MDI-QKD networks.It is often implicitly assumed that the classical post-processing units of a QKD sys-tem are trusted.This is a rather strong assumption and is very hard to justify in practice.Besides,the existence of covert channels(such as memory attacks)also threatens the security of QKD systems.In the MDI-QKD experiments foiling covert channels and un-trusted devices,we used techniques in secure multiparty computing(such as verifiable secret sharing)to realize secure communication where one of the two parties in MDI-QKD has a malicious quantum module and/or a malicious classical unit.The scheme of how to perform multi-party post-processing is also given.Meanwhile,we developed new techniques to realize high-interference visibility with a filtered light source and two-stage modulation of on-chip polarization modulator.This work provides a blueprint for QKD systems foiling covert channels and malicious post-processing units.In addition to the research of QKD,I have also designed a multi-channel coinci-dence counter for multi-photon entanglement and Boson sampling,which solves the problem of insufficient channel number and count rate of commercial products.Be-yond that,the counts of all coincidences can be accumulated in real-time.Using an octa-phase time-to-digital converter and a solution of doing on-board coincidence,we implement a 32-channel,80 MHz count rate coincidence counter.This work has been applied in ten-photon,twelve-photon entanglement and twenty-photon Boson sampling experiments.