  We show that the saturation of a multiphoton transition is accompanied by a
gradual collapse of quantum multimodality in the strong-coupling limit of the
weakly driven Jaynes-Cummings (JC) model. By means of a perturbative method, we
illustrate the prominent role of quantum fluctuations by focusing on the two
and three-photon resonance operation in a regime where the steady-state average
photon number is below or marginally above unity. We also reveal two coexistent
quantum beats in the intensity correlation function of the forwards scattered
photons. These beats, originating from the states mediating the cascaded decay,
arise as a direct consequence of the distinct JC spectrum. Their interference
coordinates with the alternation of positive and negative values of the Wigner
function around the phase-space origin in the transient conditioned on a
photodetection.
