Here, we consider a cavity with a lower frequency for this study (hω c = 1.77 eV at k ∥ = 0), which is more red-detuned compared to the curve presented in Fig. . For each initial excitation condition with a given k ∥ , we report the corresponding photonic characters |χ ph | 2 = α |c α (t = 0)| 2 of the wavepacket, defined as the sum of the photonic components of the polariton at t = 0. To determine the transport characteristics, we perform a least-square fitting of the transient MSD with the equation