Entanglement of Two-Superconducting-Qubit System Coupled with a Fixed Capacitor

We study thermal entanglement in a two-superconducting-qubit system in two cases, either identical or distinct. By calculating the concurrence of system, we find that the entangled degree of the system is greatly enhanced in the case of very low temperature and Josephson energies for the identical superconducting qubits, and our result is in a good agreement with the experimental data.