Research On Quantum Nonlocality And Multiparty Quantum Key Distribution

Bell nonlocality and quantum entanglement are essential research topics in quan-tum foundation,and are important resources for quantum information science.Bell nonlocality indicates that if a model shows Bell nonlocal correlations,the data can-not be completely predicted by local hidden variables,which is of great interests in device-independent quantum information tasks.Based on quantum entanglement states,burgeoning quantum computing protocols and quantum communication protocols have also been developed.This thesis presents the author's works on Bell nonlocality and multiparty quantum key distribution protocols during his postgraduate period,includ-ing the loophole-free Bell inequality tests,the loophole-free Hardy paradox tests and the multiparty quantum cryptographic conferencing.Firstly,inspired by the scheme of heralded spontaneous parametric down-conversion(SPDC)source,we present a loophole-free Bell inequality test scheme that employs the heralded type of entangled photon pairs.This proposal enables a much higher degree of Bell violation compared with the one using the conventional SPDC source.Secondly,based on the Clauser-Horne-Shimony-Holt(CHSH)inequality and I4422 inequality,we propose realigned Hardy paradoxes.These presented realigned Hardy paradoxes allow higher Hardy violation compared with the existing Hardy paradox schemes.Within current technologies,it is of great potential to realize device-independent quantum information processing tasks based on the realigned Hardy paradox.Thirdly,based on the quantum entanglement,we studied the multiparty quantum key distribution and propose the new-type quantum cryptographic conferencing proto-col,which can distribute information-theoretic secure keys among multiple users over long distance.Specifically,combining the idea of post-selecting Greenberger-Horne-Zeilinger(GHZ)state and recently proposed twin-field quantum key distribution pro-tocols,we present the phase-matching quantum cryptographic conferencing protocol,which is immune to all detector side-channel attacks.The presented protocol can im-prove the key generation rate from O(?N)to O(?N-1)compared with the measurement-device-independent quantum cryptographic conferencing protocol.Meanwhile,it can be easily scaled up to more parties due to its simple setup.