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)
       
Populations of the qubits states P ξ vary as time by setting the incoherent terms to zero, initially in state |↓↓,2〉. In panels (a)–(c) the coupling constant J = 3.8 (2 π  GHz) and the two-photon detuning (a) δ = 0, (b) δ = 0.1 Δ , (c) δ = J . In panels (d)–(e) the coupling constant J = 0 and the two-photon detuning (d) δ = 0, (e) δ = 0.1 Δ . The curves correspond to P |↓↓〉 (blue solid lines), P |+〉+ P |−〉 (red dotted lines), and P |↑↑〉 (green dashed lines). The other parameters are Δ 1 = Δ 2 = 15.8, g = 0.1 (all in units of 2 π  GHz) in all the five plots.