Light-matter interactions: Ultrastrong routes to new chemistry

The demonstration of strong coupling between electromagnetic fields and excited molecular states represents a powerful new strategy for controlling quantum-mechanical states and chemical reaction dynamics. Advances in nanotechnology have revived the interest in interactions between matter and localized optical phenomena. When molecules or any other quantum emitters are placed onto a plasmonic surface or into an optical cavity, changes to the molecules' optical response are known to happen, for example, causing quenching or enhancement of their optical properties. Theoretical work has shown that when Rabi splitting of an optical state exceeds about 15% of the total transition, a new regime occurs: ultrastrong coupling. This type of coupling holds numerous intriguing properties ranging from the generation of correlated photons to room-temperature Bose-Einstein condensation.