  We highlight the importance of quantum fluctuations in organizing a
dissipative quantum phase transition for the driven Jaynes-Cummings interaction
with variable qubit-cavity detuning. The system response presents a substantial
difference from the predictions of the semiclassical theory, the extent of
which is revealed in the properties of quantum bistability, and visualized with
the help of quasi-distribution functions for the cavity field, subject to an
appropriate scale parameter. States anticipated by the neoclassical theory of
radiation coexist in the quantum picture, following the occurrence of
spontaneous dressed-state polarization and phase bistability at resonance.
