Multipartite EPR Steering And Application In Secure Quantum Communication

As a frontier subject of quantum mechanics and informatics,Quantum information science is based on the basic principles of quantum mechanics,and has carried out research work in the field of the basic quantum information science and optical communication,including quantum entanglement,quantum parallelism,quantum teleportation,etc.Quantum information encode,transmission and computation are implemented based on utilizing fundamental principles of quantum mechanics and novel characteristics of quantum systems,and to improve the accuracy,speed and security of information.EPR steering is a special quantum correlation between quantum entanglement and Bell nonlocality with the inherent asymmetry,which plays an important role in quantum communication networks.Since the introduction of the concept of EPR steering,people have done a lot of relevant researches.EPR steering was first demonstrated with a two-mode squeezed state and extended to the system of multipartite,and from continuous variables system to separating variables,which also got some relevant verification in experiment.However,in response to remote transfer of quantum states,we need to explore more quantum resources.Quantum entanglement swapping is an important technique for constructing quantum communication network,which makes two quantum entangled states of independent without a direct interaction become entangled.It is verified in both the separated variable quantum system and the continuous variable quantum system.Recently,it has been proposed that the discrete variable system and the continuous variable system be swapped of entanglement,and verification of the study means that the implementation of hybrid quantum communication network and greatly enriches quantum resources.Subsequently,the application of entanglement swapping technology in Gaussian quantum steering was confirmed that steering property exists between two independent quantum states without a direct interaction after entanglement swapping by the Institute of Opto-Electronics of Shanxi University.Around the quantum steering of continuous variables,we explore the control of EPRIV steering in bipartite and multipartite entangled states by introducing noise with loss or through asymmetric modulation.The main research work of this paper is as follows:(1)Influence of Gaussian noise and the loss channel introduction on EPR steering.Based on CV quadripartite cluster entangled states,one of them and vacuum state are coupled by a tunable beam splitter,and Gaussian noise is added at one of them through a99:1 beam splitter.We quantify the different types EPR steering of new quadripartite states with the reconstructed covariance matrix.Theoretically,the EPR steering parameter versus Gaussian noise are obtained,and in the same way EPR steering characteristic versus transmission efficiency in the lossy channels is analyzed under different values of Gaussian noise.(2)We theoretically designed two schemes to change the direction of different types EPR steering by asymmetric modulation method.Two schemes,including tripartite entangled state to bipartite steering and quadripartite entangled state to tripartite steering are investigated.We quantify the steerability of multipartite entangled states with reconstructed covariance matrix,and show the EPR steering parameter versus squeezing parameters.For scheme I,the results of bipartite steering can be used to secure quantum communication protocol which including two users,and for scheme II,different types EPR steering of multipartite states which makes it easier to implement one-sided device-independent quantum key distribution(1SDI-QKD)and quantum secret sharing(QSS)protocol.(3)Based on the technology of entanglement swapping,we propose three schemes,First two of which respectively are that two quantum states can be changed by asymmetric modulation method or by introducing noise into one state and modulation to another one.No-way,one-way and two-way Steerability of two schemes are analysed and compared,the theoretical research results provide a feasible reference for the realization of the security of quantum communication.In third scheme,a tunable beam-splitter,as a steering control switch,is set during the swapping of two space-separated independent Gaussian EPR entangled states.We add vacuum state and the excess noise in this chances,by adjusting the reflection efficiency of the tunable beam-splitter and introducing noise loss,one-way and two-way asymmetric steering can be achieved.This protocol gives a feasible method to switch steering direction in quantum networks and guarantee secure quantum information.