Molecular polaritons for controlling chemistry with quantum optics

Abstract

This is a tutorial-style introduction to the field of molecular polaritons. We describe the basic physical principles and consequences of strong light-matter coupling common to molecular ensembles embedded in UV-visible or infrared cavities. Using a microscopic quantum electrodynamics formulation, we discuss the competition between the collective cooperative dipolar response of a molecular ensemble and local dynamical processes that molecules typically undergo, including chemical reactions. We highlight some of the observable consequences of this competition between local and collective effects in linear transmission spectroscopy, including the formal equivalence between quantum mechanical theory and the classical transfer matrix method, under specific conditions of molecular density and indistinguishability. We also overview recent experimental and theoretical developments on strong and ultrastrong coupling with electronic and vibrational transitions, with a special focus on cavity-modified chemistry and infrared spectroscopy under vibrational strong coupling. We finally suggest several opportunities for further studies that may lead to novel applications in chemical and electromagnetic sensing, energy conversion, optoelectronics, quantum control and quantum technology.

Polaritonic normal modes in transition state theory

“…Also, the effect on the kinetics has been observed to increase as the collective coupling intensifies, as a consequence of the large number of molecules present in a sample. 1 These observations are reminiscent of the description of light-matter coupling in terms of hybrid states known as polaritons, [7][8][9][10][11][12] which successfully explains the optical properties of these systems. [13][14][15][16][17] Recently, it has been suggested that a class of nonadiabatic charge transfer reactions would experience a catalytic effect from resonant collective coupling between high-frequency modes and infrared cavity modes; the mechanism relies on the formation of vibrational polaritons which feature reduced activation energies compared to the bare molecules.…”

On the SN2 reactions modified in vibrational strong coupling experiments: reaction mechanisms and vibrational mode assignments

“…8 These two works highlight the potential of the field of polaritonic chemistry to modify thermal reactions by taking advantage of the presence of polaritons. [9][10][11][12][13] These are the states formed when molecular transitions, such as those between vibrational states of the reactant in the case of these experiments, and confined light modes, such as those from Fabry-Pérot cavities, hybridize in the strong coupling regime. This vibrational strong coupling results in the splitting of the IR band of the coupled vibration.…”

Photoprotecting Uracil by Coupling with Lossy Nanocavities

“…The collection of models and experimental techniques aiming at controlling chemistry via coupling to quantum light goes by the name of polaritonic chemistry or molecular polaritonics. 19 − 24 In this framework the molecules are confined in optical cavities and are resonantly coupled to localized modes of the electromagnetic field. 25 − 28 Whether this coupling is strong enough to drive substantial chemical modifications depends on the specifics of the system: 29 the oscillator strength of the molecular excitation, the volume of the mode in the nanocavity, the number of molecular emitters, together with the lifetimes of the exciton and nanocavity mode.…”

“…When the coupling strength exceeds the decay rates of both the cavity mode and the exciton (strong-coupling regime), the states of the system can be suitably described as hybrids between light and matter: the polaritons. 24 Very recent theoretical works and experiments have proven that reaching the strong coupling regime is a useful way to catalyze photochemical reactions, 30 − 34 to modify the relaxation pathways of molecules, 35 − 37 and to mediate energy transport phenomena, 38 − 40 as well as to enhance the molecular optical response. 41 − 44 In the same fashion, Shegai and collaborators have shown that strong coupling to plasmonic nanoantennas can significantly increase the photostability of chromophores.…”