Research On Device Independent Quantum Key Distribution And Quantum Metrology

The origins of quantum entanglement can be traced back to the 1930s when scientists like Albert Einstein noticed that there could be counterintuitive correlations between composite quantum systems.This phenomenon was called "quantum entanglement" by Erwin Schr?dinger.Based on this,John S.Bell formalized a complete theory of quantum non-locality in the 1960s.Quantum entanglement can be seen as a valuable physical resource,and it can be used to accomplish tasks that are impossible in classical physical systems.This paper mainly introduces the application of quantum entanglement in device-independent quantum key distribution(DI-QKD)and quantum metrology.Quantum key distribution(QKD)is a protocol for exchanging keys between two remote users over an insecure quantum channel.In traditional QKD,the security is typically based on the assumption that the users’ devices are well-characterized according to security models established in security proofs.In contrast,DI-QKD allows for secure communication even without knowledge of the underlying quantum devices.Although DI-QKD is elegant in theory,it is difficult to implement with current technologies.This thesis will present the author’s theoretical research on DI-QKD.We will first review the development of DI-QKD,and then provide a detailed introduction of the methods used to prove its security.Building on this foundation,we propose a new DI-QKD protocol that incorporates random post-selection.In the model of collective attacks,we have demonstrated that our protocol can tolerate detector efficiency as low as 68.5%,which exceeds the standard security proofs and represents a significant step toward practical implementation of DI-QKD.Additionally,we will present an experimental demonstration of DI-QKD using a photonic setup.By modeling the noise in the actual optical system and identifying the problems that need to be solved to realize DI-QKD,we have proposed a new DI-QKD protocol that combines different approaches such as random post-selection,noisy preprocessing,and full statistics to overcome the noise introduced by device imperfections.We have shown that this new protocol only requires a global detection efficiency of 86.2%to generate positive keys,and we have achieved a proofof-principle verification of photonic DI-QKD based on this protocol.Our results are of significant importance for the application of photonic DI-QKD.This thesis will also introduce the author’s theoretical work in distributed quantum metrology.We will first introduce the precision limits in multi-parameter distributed quantum metrology.Based on this,we theoretically propose an experimentally feasible discrete-variable distributed quantum sensing scheme,whose phase measurement accuracy is close to the Heisenberg limit.We have also completed the experimental demonstration of this scheme,which uses six-photon entangled photons,and each photon passes through a phase shift element up to six times,resulting in a total of 21 equivalent photons,with a phase measurement accuracy below the short-noise limit of 4.7 dB.Considering that most previous distributed quantum sensing experiments were accomplished in laboratory environments and did not truly achieve spatial separation,we propose and implement an experimentally feasible discrete-variable distributed quantum sensing experiment scheme in field.The experiment achieved an unconditional violation(without post-selection)of shot-noise limit up to 0.916 dB for the field distance of 240 m.These results represent an important step towards the practical application of quantum sensing networks.