Fig. depicts the potential energy surface for the photon dressed adiabatic states |Φ α , n , as well as the polariton potential associated with the ground state |Ψ 0 . Near the barrier region (R ≈ 0), the ground adiabatic state coincides with the covalent diabatic state |C , where the ground state potential is nearly identical to MH diabatic potential V C (R) for R ≈ 0. Thus, for this three-level Shin-Metiu system even in the infinite light-matter coupling limit, the ground state potential near the barrier region will not be modified as it is already very close to the MH diabatic state. In contrast, the ground state potential can be expected to get significantly modified near the donor and acceptor wells as the ground state is formed by hybridiz-ing the |D or |A with the |C states through a diabatic coupling. Increasing light-matter coupling effectively decreases the diabatic coupling 0 C |0 D • V DC due to the decreasing 0 C |0 D (with a similar effect for 0 C |0 A • V AC ). Thus, it will bring the ground state potential closer to the MH diabats' potential energy surface, as suggested in Eq. 17. This means that near ground state potential minima (for R ≈ -5.5 and R ≈ 5.5), the ground state polariton potential will be pushed upwards as it approaches the MH diabats lying above, thus effectively reducing the ground state barrier height.