Measurement of ac Stark shift in a superconducting qubit under strong Rabi drive

We present a measurement of ac Stark shift in a superconducting 3D transmon qubit. The qubit is strongly coupled to a superconducting aluminum cavity in circuit QED architecture. We observed the ac Start shift under strong Rabi drive and measured it from detuning behavior of the Rabi oscillations as a function of the Rabi frequency. We also confirmed the shift by the Autler-Townes splitting measurement as a function of the qubit drive power.