Thermal entanglement of superconducting qubits for arbitrary interaction strength

Abstract: We investigate the thermal entanglement in two superconducting qubits for arbitrary interaction strength and ground state frequencies. We calculate the concurrence of the system to quantify the thermal entanglement. We suggest a scheme, where an external tunable coupler qubit sandwich between two superconducting qubits generates entanglement. The behavior of concurrence is analyzed for three different cases, in which we consider the effects of the temperature, the qubit-qubit effective coupling strength, and the qubit frequencies on the thermal entanglement. What deserves mentioning here is that to achieve maximally entangled states, it is better to use two superconducting qubits with the same frequencies. We also note that for a given temperature, the thermal entanglement can be tuned by qubit internal capacitance and inductance.