The Study On Pairwise Thermal Entanglement In A Ring Of N Spin Particles

When Einstein, et al put EPR Paradox forward in 1935, physical scientists had paid attentiort to the specialities of quantum states about entanglement. With the development of quantum information theory and advance of quantum computer, quantum entanglement have been applied to quantum calculation, information and quantum communication as a important resource. Entanglement can realize quantum cryptography, quantum teleportation and quantum long communication, et al ,which are difficult to be realized by classical methods. Entanglement has the properties of inartificial secrecy, superhigh speed and super volume, is the important physical quantity to realize the hardware of quantum computer. The deep study about entanglement will affect not only quantum information basic theory but also the future potential practical application.In this paper, we mainly study pairwise thermal entanglement of thermal equilibrium state in a canonical ensemble. Firstly we study pairwise entanglement of the system withHamiltonian is and , and discussthe relations between the concurrence, an entanglement measure for two qubits, with thermodynamic function, internal energy U . Then we give general form of the concurrenceand we discuss the effect of the magnetic field on the entanglement.