Dynamics of two-level systems beyond the rotating-wave approximation J. Song, Y. Xia, X.D. Sun, Y. Zhang, B. Liu and H.S. Song Eur. Phys. J. D, 66 4 (2012) 90 Published online: 19 April 2012 DOI: 10.1140/epjd/e2012-20523-9