Photon number splitting is observed in a transmon coupled to a superconducting quasi-lumped-element resonator in the strong dispersive limit. A thermal population of 5.474 GHz photons at an effective resonator temperature of T = 120mK 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.
@article{arxiv.1308.2246,
title = {Observation of Autler-Townes effect in a dispersively dressed Jaynes-Cummings system},
author = {B. Suri and Z. K. Keane and R. Ruskov and Lev S. Bishop and Charles Tahan and S. Novikov and J. E. Robinson and F. C. Wellstood and B. S. Palmer},
journal= {arXiv preprint arXiv:1308.2246},
year = {2013}
}