We have observed the Autler-Townes doublet in a superconducting Al/AlOx/Al transmon qubit that acts as an artificial atom embedded in a three-dimensional Cu microwave cavity at a temperature of 22 mK. Using pulsed microwave spectroscopy, the three lowest transmon levels are isolated, eliminating unwanted effects of higher qubit modes and cavity modes. The long coherence time (~40 us) of the transmon enables us to observe a clear Autler-Townes splitting at drive amplitudes much smaller than the transmon level anharmonicity (177 MHz). Three-level density matrix simulations with no free parameters provide excellent fits to the data. At maximum separation, the fidelity of a dark state achieved in this experiment is estimated to be 99.6-99.9%.
@article{arxiv.1308.0520,
title = {Autler-Townes splitting in a three-dimensional transmon superconducting qubit},
author = {S. Novikov and J. E. Robinson and Z. K. Keane and B. Suri and F. C. Wellstood and B. S. Palmer},
journal= {arXiv preprint arXiv:1308.0520},
year = {2013}
}