Observation of Autler-Townes effect in a dispersively dressed Jaynes-Cummings System

We report on the spectrum of a superconducting Al/AlOx/Al transmon qubit coupled to a planar superconducting resonator in the strong dispersive limit. We resolve discrete peaks in the transition spectrum, each corresponding to a different number of photons. At a base temperature of 30 mK and in the absence of a coherent drive on the resonator, we find a weak n = 1 photon peak along with the n = 0 photon peak in the qubit spectrum, corresponding to a population of 5.474 GHz photons at an effective resonator temperature of T = 120mK. Two-tone spectroscopy using independent coupler and probe tones reveals an Autler-Townes splitting in the thermal n = 1 photon peak. The observed effect is explained accurately using the four lowest levels of the dispersively dressed qubit-resonator system and compared to results from numerical simulations of the steady-state master equation for the coupled system.