Fig. and Fig. present intensities of the lower diagonal and upper cross-peaks as a function of t 2 , with Γ = 0 meV, and various light-matter coupling strengths g c . The orange curve corresponds to the 2DES peak intensities of a molecular system outside the cavity (or g c = 0). As we can see, there is no apparent coherent oscillation in the system due to the large reorganization of the phonon bath that causes fast decoherence. When coupling to the cavity, we see that with an increase in the light-matter coupling, the coherence oscillations become more prominent and last for more than 200 fs at room temperature. This is caused by the polaron decoupling mechanism, as explained by Eq. 46. This is because by coupling to the photonic DOFs, the effective coupling between the polariton state and the phonon (nuclei) is reduced. Therefore, coupling molecules to an optical cavity can provide a way to prolong the coherence of the hybrid system compared to the bare molecules. Similar enhanced electronic coherence has been experimentally observed by collectively coupling organic molecules with the optical cavity. Again, the characteristic phonon frequency ω 0 = 200 cm -1 used in this model is much smaller than the Rabi splitting created in this case, so the oscillation observed in Fig. is less likely due to the vibrational coherence as often observed in natural light-harvesting systems. Fig. and Fig. present the intensities of the lower diagonal and upper cross peaks, respectively, as a function of t 2 with the light-matter coupling strength of ℏg c = 500 cm -1 (62 meV) for various cavity loss rates. As can be suspected, adding cavity loss causes an equivalent effect to adding a dissipative bath for the cavity mode. Thus, with an increased cavity loss, one observes an increase in the decoherence among polariton states. It should be noted that even for an experimentally accessible cavity loss rate of Γ = 10 meV and Rabi splitting Ω R = 2ℏ c ≈ 124 meV) we still observe a long-lived polaritonic coherence (for t > 200 fs) at room temperature, much longer than the typical electronic decoherence of the molecule (see the orange curve in Fig. ) whose exciton-phonon re-organization energy is λ = 24.8 meV (200 cm -1 ). Similar experimental conditions for the λ, Γ and Ω R have been recently achieved when coupling CdSe nanoplatelets to a dielectric optical cavity.