Entanglement control in an anisotropic two-qubit Heisenberg XYZ model with external magnetic fields

We study the bipartite entanglement dynamics in an anisotropic two-qubit Heisenberg XYZ model under the influence of population relaxation and in the presence of various types of magnetic fields. We find that the maximal value of the concurrence has an intrinsic rigidity for the different external magnetic fields. Moreover, our results demonstrate that it is possible to produce entangled states and to control or to modulate the concurrence within the intrinsic maximal value with the help of external time-varying fields despite the existence of dissipation.