A scheme for two-photon lasing with two coupled flux qubits in circuit quantum electrodynamics*
Huang Wena),b), Zou Xu-Boa),b)†, Guo Guang-Cana),b)
       
(a) Schematic diagram for a coupled system of two flux qubits and a transmission line resonator. The two qubits are coupled inductively. (b) The level diagram for the two qubits. The red double arrows show the couplings with the resonator, and the dark blue double arrow shows the coupling between the two qubits.