Driven dynamics of a qubit tunably coupled to a harmonic oscillator*

We have investigated the driven dynamics of a superconducting flux qubit that is tunably coupled to a microwave resonator. We find that the qubit experiences an additional oscillating field mediated by off-resonant driving of the resonator, leading to unanticipated, strong modifications of the qubit Rabi frequency. Low-frequency noise in the coupling parameter translates to an effective noise in the amplitude of the drive field, causing a reduction of the coherence time during driven evolution. The noise can be mitigated with the rotary-echo pulse sequence, which, for driven systems, is analogous to the Hahn-echo sequence.