Various Quantum Correlations In Two-Qubit One-Axis And Two-Axis Spin Squeezing Model In Thermal Equilibrium Under An External Magnetic Field

Quantum entanglement is one of the most important material resources in quantum information theory.It plays a crucial role in quantum cryptography,quantum teleportation,dense coding,quantum computation and so on.The quantum computer,which is the hot spot of recent research,is a kind of equipment which is calculated by quantum logic.Quantum logic is a gate circuit based on the principle of quantum mechanics.The quantum gate circuit takes the entangled particles as the resource.However,entanglement is affected by the environment too much,and as the study is further discovered,In addition to entanglement,There are other ways to measure quantum correlation,such as quantum discord,geometric quantum discord,stable quantum disassociation,super quantum discord,local measurement caused by weak measurement and so on.Most recent researchers are interested in quantum discord,geometric quantum discord,and find that their ability to resist environmental interference is better than entanglement.This dissertation is based on the spin squeezing one-axis twisting model and the spin squeezing two-axis countertwisting model.A complete introduction to the spin squeezing model and its characteristics,as well as the effects of the three quantum correlations under the single axis and the biaxial model of the spin squeezing model of environmental factors.First,the recent research status and recent progress of quantum information and quantum communication are introduced.Then,we review the basic knowledge in this paper,including quantum bit,quantum gate,quantum entanglement,quantum discord,geometric quantum discord,spin squeezed state.Two methods to realize the spin squeezing state are introduced in detail.The one-axis twisting model(OATM)and the two-axis countertwisting model(TACM).In the third chapter,focuses on the introduction of the various quantum correlations of the spin squeezing two-axis countertwisting model in thermal equilibrum under the external magnetic field are introduced.The effects of the spin squeezing parameters,the system temperature and the external magnetic field on the entanglement,quantum correlation and geometric quantum correlation in the model are studied.The results show that the spin squeezing parameters play an active role in the three correlations,and the external magnetic field and the system temperature have a weakening effect on the quantum correlation.The only exception is that theexternal magnetic field has a positive effect on the quantum correlation at higher temperatures.It is also found that the dependence of the quantum correlation on the spin squeezing parameters is smaller than that of the entanglement concurrence and the geometric quantum correlation.In the end of this thesis,based on previous studies,the geometric quantum correlations of the spin squeezing one-axis twisting model is analyzed.And the ability of three kinds of correlations to resist environmental disturbance is compared under the same system parameters.The results show that the quantum disassociation is better able to resist environmental interference,followed by geometric quantum disassociation,and the entanglement is easily damaged by environmental shadow.