  Rabi oscillations is a key phenomenon among the variety of quantum optical
effects that manifests itself in the periodic oscillations of a two-level
system between the ground and excited states when interacting with
electromagnetic field. Commonly, the rate of these oscillations scales
proportionally with the magnitude of the electric field probed by the two-level
system. Here, we investigate the interaction of light with a two-level quantum
emitter possessing permanent dipole moments. The semi-classical approach to
this problem predicts slowing down and even full suppression of Rabi
oscillations due to asymmetry in diagonal components of the dipole moment
operator of the two-level system. We consider behavior of the system in the
fully quantized picture and establish the analytical condition of Rabi
oscillations collapse. These results for the first time emphasize the behavior
of two-level systems with permanent dipole moments in the few photon regime,
and suggest observation of novel quantum optical effects.
