Research On Quantum Entanglement And Its Non-Locality In Quantum Communication

Quantum communication is a method with unconditional security in the process of information transmission,and its core is quantum key distribution(QKD).Security of QKD is mainly based on quantum no-cloning theorem and Heisenberg uncertainty principle,which theoretically meets the requirements of the "one time one key"encryption system.In practical applications,the ideal conditions required by the QKD protocol are difficult to achieve.Therefore,further,the measurement device-independent quantum key distribution(MDI-QKD)is based on QKD,which is effective It solves the quantum hacker attack on the detector side,and at the same time uses the advantages of its structure to extend the communication distance twice.The existing MDI-QKD protocol usually uses weak coherent photons(WCP).WCP is obtained by attenuating the laser,but one of its problems is that the photon number distribution follows the Poisson distribution,which makes the vacuum state ratio as high as 60%,while the single-photon ratio is less than 30%.The use of WCP light source makes the protocol vulnerable to Photon Number Separation(PNS)attacks.At the same time,the current polarization-based protocols have the problem that the reference system depends on the calibration of the basis.Moreover,the polarization state produces ecological drift in the communication process,which will affect the key rate.In order to solve the above problems,we propose the MDI-QKD protocol based on the parametric light source and orbital angular momentum(OAM).At the same time,for quantum communication,its future must be based on quantum networks.Nonlocality in quantum networks plays an important role in the research of quantum network communication.However,in quantum networks,the characterization of quantum non-locality is very difficult,especially in the case of multiple sources and multiple participants.In view of this,this paper proposes proof of the non-locality of a quantum network based on a mixed state composed of a three-particle entangled W state and other entangled states.The main research contents of this paper are as follows:(1)This paper proposes the MDI-QKD communication protocol based on parametric light sources and OAM.This protocol combines the parametric light source with OAM,making the performance of the MDI-QKD protocol gradually approach the ideal situation.The parametric light sources used in this article mainly include single-photon-added-coherent(SPACS)and heralded single-photon sources(HSPS).This article first introduces the OAM-MDI-QKD protocol based on SPACS light source.The SPACS light source does not contain vacuum state,and its light source contains a high proportion of single photons.This advantage of SPACS,combined with OAM's independence from base and decoy method,makes the protocol approach the ideal situation gradually.The HSPS eliminates most of the vacuum state by marking one of the photon pairs generated in the parametric down conversion,thereby increasing the key rate and increasing the maximum secure distance.(2)Next,this paper analyzes the security of the OAM-MDI-QKD protocol based on SPACS and HSPS light sources,then performs numerical simulations.The OAM-MDI-QKD protocol based on two parametric light sources proposed in this paper is compared with the OAM-MDI-QKD protocol based on WCP.The protocol compares the two performance indicators of key rate and maximum secure distance.Through numerical simulation,the results show that,compared with the protocol based on the WCP light source,the protocol based on the two parametric light sources of HSPS and SPACS has higher photon utilization and longer transmission distance,and the maximum safe transmission distance is respectively increased by 30km and 40km.(3)Finally,this paper proposes a proof of non-locality of quantum network based on three-particle entangled W states for the application of quantum communication in quantum network.This proof uses the W state as the quantum source,constructs the measurement basis for the W state,calculates its key values,and obtains its violation of the nonlinear Bell inequality,which proves the non-locality of the quantum network.Next,this paper uses the mixed state of the W state and the bipartite entangled pure state as the quantum source,and at the same time extends this measurement method to a quantum network with N parties,which proves that the non-locality of the N-party quantum network is established.In addition,in order to verify whether the research have practical effect,noise is added,and when the calculation contains noise,the violation of quantum non-locality is still valid,which proves that the existence of noise is allowed in the multiparty quantum network based on the W state.