Ref. 123 investigates ballistic transport in excitonpolaritons by tuning the polariton-phonon through light-matter interactions. The polariton-phonon coupling can be modified because the exciton couples to the phonon but the cavity excitation does not, and as a result, the phonon coupling strength directly depends on the excitonic character of the polariton which can be modulated by detuning. They find that the ballistic motion of polariton propagation can be observed even at high exciton content (∼ 25% excitonic) but with a reduced group velocity. Their quantum dynamics simulations indicate that the origin of this group velocity re-scaling originates from a transient localization process induced by the weak interactions to phonon. 123