Fig. 5: Switching our circuit between a fluxonium and an oscillator with high order interactions.
From: Spectral signature of high-order photon processes enhanced by Cooper-pair pairing
a, b Potential energy \(U(\varphi )=\frac{1}{2}{E}_{L}{\varphi }^{2}-{E}_{J1}\cos (\varphi -{\varphi }_{{{{\rm{ext}}}}})+{E}_{J2}\cos [2(\varphi -{\varphi }_{{{{\rm{ext}}}}})]\) as a function of superconducting phase at φext = 0.9π [starred in (c, d)], for (a) θext = 0 and (b) θext = π. c, d Transition frequencies from the ground state as a function of external flux. The data points (open circles) correspond to the average of resonances visible in scans such as Fig. 4(c, d). Theoretical transition energies (solid lines) are obtained from Hamiltonian (4) with fitted parameters reported in Table 2.
