These light-matter hybrid PESs E ± (R), so-called polaritonic PESs, adapt their curvature from both the ground and the excited state PESs and depend on the light-matter coupling strength ℏg c and the cavity photon frequency ℏω c . Therefore, the excited state potential energy landscape, and consequently the photochemistry of the cavity-molecule system, is modified with ℏg c and ℏω c acting as tuning knobs to control the molecular excited state dynamics. Note that within the approximated JC model, the |g, 0⟩ state has the PES E g (R) + ℏωc 2 which is the same as the molecular ground state |g⟩ other than the irrelevant zero-point energy shift of ℏωc 2 . This change of PES landscape is the central idea of polariton photochemistry (in the single molecule coupled to a single radiation mode limit) which will be discussed in detail in Sec. 3-4. Details of the rigorous light-matter Hamiltonian, as well as various approximate ones (such as the JC model), and their applicability are discussed in Sec. 2.