Cavity Quantum Electrodynamics of Molecular Systems Polarization Effects, Multiple Excitations, and Vibrational Selectivity

by Lucas Garcia Borges (Stockholm University)

Monday 8 Dec 2025, 13:00 → 16:00 Europe/Stockholm

FA32 (AlbaNova Main Building)

Abstract
The field of Polaritonic Chemistry studies molecules strongly coupled to the light field of optical cavities. The resulting
modification of the potential energy landscape has been demonstrated to enable control over the chemical and physical
properties of materials and molecular ensembles.
This thesis extends the Tavis–Cummings model to describe molecules under strong light–matter coupling, incorporating
static dipole moments and dipole self-energy contributions derived from the Pauli–Fierz Hamiltonian. These additional
terms are shown to be essential for reproducing cavity-modified molecular dynamics and spectra. Simulations on the nuclear
wavefunction propagation of MgH+ molecules demonstrate the impact of these terms, while an effective two-level system
model accurately captures the behavior of large ensembles.
Beyond single excitations, the thesis also explores the higher excitation manifolds of the Tavis-Cummings model, which
reveals that allowing for more than a single excitation makes the reaction of the involved polaritons entropically more
favorable. Open-system simulations highlight how the coherence of the system's initial state governs decay pathways and
enables long-lived energy storage.
Finally, a multilevel vibrational model coupled to a two-mode cavity is introduced, where a Raman scheme enables
selective mixing of vibrational states. The simulation results show that continuous pumping can drive molecules into
specific vibrational states while suppressing electronic excitation, both for single molecules and small ensembles.
Together, these results provide new theoretical insights into the mechanisms by which optical cavities reshape molecular
energy landscapes. The results suggest approaches for controlling photonic, electronic, and vibrational dynamics in strongly
coupled systems, contributing to the theoretical foundation of polariton chemistry.