The cavity mode in the single excitation subspace is treated as a two-level system with states |0⟩, which is the vacuum 0-photon Fock state whose energy is set to 0 for convenience, and |1⟩, which is the 1-photon Fock state with energy hω c . In the combined molecule-cavity Hilbert space which is restricted to zero and single-excitation states (see Fig. ), we label the states in a condensed fashion (e.g., |G⟩ ⊗ |1⟩ ≡ |G, 1⟩). For brevity, further labels of excited molecular states without a Fock state label are assumed to have 0 photons (e.g., |A j ⟩ implies |A j , 0⟩).