Thermal Entanglement in Superconducting Quantum-Interference-Device Qubits Coupled to Cavity Field

We investigate thermal entanglement in a superconducting-quantum-interference-device qubit coupled to a cavity field. We show that the entanglement can be manipulated by varying temperature and an effective controlling parameter B which depends on the external field and characteristic parameters of the system. We find that there exists a critical value of the controlling parameter B_c. Under a fixed temperature, increasing B can increase entanglement in the regime of B < B_c, while the entanglement decreases with increasing B in the regime of B > B_c.