Charge qubit driven via the Josephson nonlinearity

We study the novel nonlinear phenomena that emerge in a charge qubit due to the interplay between a strong microwave flux drive and a periodic Josephson potential. We first analyse the system in terms of the linear Landau–Zener–Stuckelberg model, and show its inadequacy in a periodic system with several Landau–Zener crossings within a drive period. Experimentally, we probe the quasienergy levels of the driven qubit with an LC cavity, which requires the use of linear response theory. We show also that our numerical calculations are in good agreement with the experimental data.