Entanglement in a three-qubit anisotropic Heisenberg XXZ spin ring with Dzyaloshinskii-Moriya interaction

We investigate the entanglement of a three-qubit anisotropic Heisenberg XXZ ring with Dzyaloshinskii-Moriya (DM) interaction in thermal equilibrium at temperature T in the presence of an external magnetic field B along the z-axis and obtain analytic expression for the concurrence, in which the dependence of the concurrence on the anisotropic coupling coefficient J_z, external magnetic field B, the DM interaction parameter D and temperature T is described. The DM interaction is found to have a more significant role than the others in increasing the critical temperature or the entanglement area. We also calculate the ground-state entanglement under various control parameters and give expressions for the quantum critical points at which quantum phase transition (QPT) takes place. These results show that one is able to produce, when it does not exist, or increase (up to some limit), when it exists, the concurrence so that the efficient control of entanglement by appropriate combinations of the tunable parameters may be possible.