Theoretical Advances in Polariton Chemistry and Molecular Cavity Quantum Electrodynamics

When molecules are coupled to an optical cavity, newlight-matterhybrid states, so-called polaritons, are formed due to quantum light-matterinteractions. With the experimental demonstrations of modifying chemicalreactivities by forming polaritons under strong light-matterinteractions, theorists have been encouraged to develop new methodsto simulate these systems and discover new strategies to tune andcontrol reactions. This review summarizes some of these exciting theoreticaladvances in polariton chemistry, in methods ranging from the fundamentalframework to computational techniques and applications spanning fromphotochemistry to vibrational strong coupling. Even though the theoryof quantum light-matter interactions goes back to the midtwentiethcentury, the gaps in the knowledge of molecular quantum electrodynamics(QED) have only recently been filled. We review recent advances madein resolving gauge ambiguities, the correct form of different QEDHamiltonians under different gauges, and their connections to variousquantum optics models. Then, we review recently developed ab initioQED approaches which can accurately describe polariton states in arealistic molecule-cavity hybrid system. We then discuss applicationsusing these method advancements. We review advancements in polaritonphotochemistry where the cavity is made resonant to electronic transitionsto control molecular nonadiabatic excited state dynamics and enablenew photochemical reactivities. When the cavity resonance is tunedto the molecular vibrations instead, ground-state chemical reactionmodifications have been demonstrated experimentally, though its mechanisticprinciple remains unclear. We present some recent theoretical progressin resolving this mystery. Finally, we review the recent advancesin understanding the collective coupling regime between light andmatter, where many molecules can collectively couple to a single cavitymode or many cavity modes. We also lay out the current challengesin theory to explain the observed experimental results. We hope thatthis review will serve as a useful document for anyone who wants tobecome familiar with the context of polariton chemistry and molecularcavity QED and thus significantly benefit the entire community.

Automated summary

This article summarizes some of the theoretical advances in polariton chemistry, covering fundamental frameworks, computational techniques, and applications in fields such as photochemistry and vibrational strong coupling. It highlights the importance of the theory of quantum light-matter interactions and discusses recent progress in resolving challenges in quantum electrodynamics.