  The coherent evolution of the atom-cavity state in bimodal (cavity)
experiments has been analyzed for a realistic time-dependence in detuning the
atomic transition frequency. Apart from a `smooth switch' of the atomic
resonance from one to the second mode of a bimodal cavity, we considered also
an additional (effective) interaction between the field modes of the cavity,
known as `communication channel'. Comparison of our model computations has been
made especially with the measurements by Rauschenbeutel et al., [2001 Phys.
Rev. A 64 050301] who demonstrated for the first time the entanglement of the
field modes in a bimodal cavity. It is shown that the agreement between the
(theoretically) predicted and experimental phase shifts can be improved by
allowing a `communication' between the two field modes during a short but
finite switch of the atomic transition frequency from one mode to the other. We
therefore suggest that the details of the atom-cavity detuning should be taken
into account for the future interpretation of bimodal cavity experiments.
