B. Suri, Z. K. Keane, R. Ruskov, Lev S. Bishop, Charles Tahan, S. Novikov, J. E. Robinson, F. C. Wellstood, B. S. Palmer

We report on the spectrum of a superconducting transmon device coupled to a planar superconducting resonator in the strong dispersive limit where discrete peaks, each corresponding to a different number of photons, are resolved. A thermal population of 5.474 GHz photons at an effective resonator temperature of T = 120 mK results in a weak n = 1 photon peak along with the n = 0 photon peak in the qubit spectrum in the absence of a coherent drive on the resonator. 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.

Observation of Autler-Townes effect in a dispersively dressed Jaynes-Cummings system (http://iopscience.iop.org)