Superconducting qubits acting as artificial two-level atoms allow for controlled variation of the symmetry properties which govern the selection rules for single and multiphoton excitation. We spectroscopically analyze a superconducting qubit-resonator system in the strong coupling regime under one- and two-photon driving. Our results provide clear experimental evidence for the controlled transition from an operating point governed by dipolar selection rules to a regime where one- and two-photon excitations of the artificial atom coexist. We find that the vacuum coupling between qubit and resonator can be straightforwardly extracted from the two-photon spectra where the detuned two-photon drive does not populate the relevant resonator mode significantly.
@article{arxiv.1107.0810,
title = {Selection rules in a strongly coupled qubit-resonator system},
author = {T. Niemczyk and F. Deppe and E. P. Menzel and M. J. Schwarz and H. Huebl and F. Hocke and M. Häberlein and M. Danner and E. Hoffmann and A. Baust and E. Solano and J. J. Garcia-Ripoll and A. Marx and R. Gross},
journal= {arXiv preprint arXiv:1107.0810},
year = {2011}
}