Quantum Dynamics Simulations of Polariton Transport in a Bloch Surface Wave Cavity.

Coupling excitons to quantized cavity photonic modes can significantly enhance the spatial and temporal range of excitonic transport. The formation of hybrid light-matter states, known as polaritons, plays a central role in this enhancement. Polaritons, owing to their photonic character, can greatly amplify coherent energy flow in excitonic systems and prolong their lifetime, and lead to ultrafast ballistic excitonic transport, which is typically diffusive outside a cavity. In Bloch surface wave (BSW) cavities, the group velocity of these polaritonic wavepackets has been theoretically predicted to approach the speed of light in the medium, though experiments suggest a renormalized value. In this work, we use quantum dynamics simulations with theoretical analysis on group velocity renormalization and wavepacket evolution to elucidate the transport dynamics in a Bloch Surface Wave Cavity. We show that polaritonic states facilitate ballistic flow directly through their photonic character, and that below a critical photonic fraction the ballistic component is suppressed-yet even then, transport remains four to eight orders of magnitude faster than purely excitonic diffusion. These results show qualitative, and in some cases near-quantitative agreement with experimental trends, providing microscopic insight into the origin of fast transport in BSW polariton systems.