Frank Deppe, Matteo Mariantoni, E. P. Menzel, A. Marx, S. Saito, K. Kakuyanagi, H. Tanaka, T. Meno, K. Semba, H. Takayanagi, E. Solano, R. Gross: Two-photon probe of the Jaynes-Cummings model and controlled symmetry breaking in circuit QED. 2008Nature Physics: 4. ISBN 1745-2473 http://dx.doi.org/10.1038/nphys1016