  We use the polarized Fock states to describe the coupled molecule-cavity
hybrid system in quantum electrodynamics. The molecular permanent dipoles
polarize the photon field by displacing its vector potential, leading to
non-orthogonality between the Fock states of two different polarized photon
fields. These polarized Fock states allow an intuitive understanding of several
new phenomena that go beyond the prediction of the quantum Rabi model, and at
the same time, offer numerical convenience to converge the results. We further
exploit this non-orthogonality to generate multiple photons from a single
electronic excitation (downconversion) and control the photochemical
reactivity.
