  he effect of the counter-rotating terms in the Jaynes-Cummings model is
investigated with an extended coherent-state approach. The counter-rotating
terms greatly modify the vacuum Rabi splitting. Two peaks with different
heights in the weak coupling regime and more than two peaks in the intermediate
coupling regime are predicted. The collapses and revivals in the evolution of
the atomic population inversion disappear in the intermediate coupling regime,
but reappear in the strong coupling regime. This reappearance is similar to
that under the rotating-wave approximation, attributed to the summation of
periodic cosine functions of the evolution.
