We investigate the thermal entanglement in the two-qubit Heisenberg XY model with a nonuniform magnetic field. Concurrence, the measurement of entanglement, is calculated. The behavior of concurrence is present at three different cases. Contrary to the uniform magnetic field case, we find that the entanglement and the critical temperature $T_C$ may be enhanced under a nonuniform magnetic field.

• Received 23 May 2003

DOI:https://doi.org/10.1103/PhysRevA.68.044301