which corresponds to a generalized diffusion equation. The constant D represents the generalized diffusion coefficient, while the exponent γ characterizes the transport properties. For γ = 1, the transport is diffusive, for γ = 2, the transport is ballistic, 1,3 and for γ < 1, the transport is subdiffusive. Fig. presents the time-dependent MSD (Eq. 7). We find that there are two separate transport stages, one at early times with γ ≈ 2 (with black solid lines as the fitting lines) and one at later times, with γ ≈ 1 (red solid lines as fitting lines). The duration of the ballistic stage depends on the photonic character of the wavepacket at t = 0. For small photonic characters (|χ ph | 2 = 0.45), the ballistic stage lasts for up to 50 fs while for large photonic characters (|χ ph | 2 = 0.75), the ballistic stage lasts for a longer duration of up to 100 fs. Further, the wavepacket transitions from purely ballistic (|χ ph | 2 = 0.75) to purely diffusive (|χ ph | 2 = 0.35) transport as |χ ph | 2 decreases. This suggests that for the initial polariton wavepacket, the transport is ballistic for a duration (with v g being renormalized by exciton-phonon coupling and cavity loss), before gradually becoming diffusive. This observation is in close agreement with recent experiments (e.g., Fig. Note that even under the diffusive transport stage (γ ≈ 1) the group velocity is still much larger than the expected gradient of matter dis-persion (which is 0 in the current model). Also, the absolute value of MSD depends on the group velocity, and with a large photonic contribution |χ ph | 2 = 0.75, the gradient of the LP dispersion is relatively small (close to a small k ∥ value in FP cavity as indicated in Fig. ). As such, for |χ ph | 2 = 0.75, even though the transport is ballistic for the longest time (for t < 100 fs) compared to the other cases investigated here, the MSD is not necessarily the largest.