Pairwise thermal entanglement in a three-qubit Heisenberg XX model with a nonuniform magnetic field and Dzyaloshinski–Moriya interaction

Pairwise thermal entanglement in a three-qubit Heisenberg XX model is investigated when a nonuniform magnetic field and the Dzyaloshinski–Moriya interaction are included. We find that the nonuniform magnetic field and Dzyaloshinski–Moriya interaction are the more efficient control parameters for the increase of entanglement and critical temperature. For both the nearest neighbour sites and the next nearest neighbour sites, the magnetic field can induce entanglement to a certain extent and the Dzyaloshinski–Moriya interaction can enhance the entanglement to a stable value. The steady value of the nearest neighbour site entanglement C₁₂ is larger than the next nearest neighbour site entanglement C₁₃. An interesting phenomenon is that the entanglement curve of C₁₂ appears a peak value when the Dzyaloshinski–Moriya interaction is considered in a nonuniform magnetic field.