Investigation of decoherence of superconducting flux qubit entangled with the environment

In the Born-Markov approximation, decoherence property of superconducting quantum circuit with a flux qubit is investigated. Using Kirchhoff's laws of classical circuit and quantum theory, we derive a Hamiltonian of the circuit. Then, combining with the Bloch-Redfield equation and in the two-level approximation, the energy relaxation time and the decoherence time of superconducting qubits is studied. Compared to the spin-boson model, this method not only investigates a decoherence being caused by the dissipative environment, but also the decoherence being generated by the dissipative elements in a superconducting electronic circuit. Hence, it is good for studying the decoherence of superconducting qubits.