where q 2 c , one may notice that the QED Hamiltonian is simply shifted in the position coordinate qc by the value -q 0 ν (R) and is hence a shifted harmonic oscillator (or "polarized Fock state" since the field is polarized by the molecular electric multipole), unique for each MH electronic state (|φ ν ⟩). At zero light-matter coupling or infinitely large cavity frequency, the original MH and un-shifted (or "vacuum") Fock states are returned. The light-matter Hamiltonian (Eq. 22) can be now block-diagonalized using the polarized Fock state basis (PFS) { |n ν (R) ⟩ } for each MH state |φ ν ⟩, which is defined as,