Ref. 212 shows that chemical reactions in an ensemble of molecules can be triggered by a single photon when all molecules are coupled to a cavity photon mode. They represent each molecule with a one-dimensional reaction coordinate resembling an isomerization reaction. The ground state potential (blue solid line in Fig. ) is characterized by a double-well potential with a large barrier between the left and the right wells corresponding to the product and reactant, respectively. As also explained before (such as in Fig. ), the excited state potential energy landscape for a single molecule can be modified by coupling to cavity (with a specific photon frequency) such that photo-excitation leads to 100% product which is shown in Fig. . In such a scenario, the initially photo-excited molecule emits a photon inside the cavity as it reaches the local minima on the product side (the minima originates from the |G, 1⟩ state which is the ground state with 1 photon in the cavity) on the polaritonic potential energy surface. When multiple molecules are present in the cavity, the photon emitted at the end of one molecule reacting (reaching the local minima in the polariton potential energy surface) can be reabsorbed by another molecule, which then can undergo chemical reactivity. This is illustrated in Fig. where the polariton potential energy surface for two molecules coupled to a cavity mode is shown. The potential energy surface in Fig. reveals that the formation of the two product molecules follows a downhill process, and this photochemical reactivity can be triggered using just one photon. Thus, the quantum yield, defined as the number of products created per photon consumed, goes beyond unity. The same has also been shown beyond two molecules in Ref. 212. Thus, the photon here acts as a catalyst that is recycled between successive molecules that undergo chemical reactivity.