Strong coupling of molecules with light leads to two remarkable features: modified energy levels and the delocalization of energy. Strong coupling may enable the creation of an entirely new class of materials. We will build on a series of recent ground-breaking experiments pioneered by Thomas Ebbesen in Strasbourg that have highlighted the power of the strong coupling concept. Although some of these reports are still controversial, changes in energy levels are predicted to: modify chemical reactions, manipulate phase transitions, change material work-functions, and control intermolecular energy transfer, whilst the delocalization of energy might even help control the conduction of electricity. These dramatic results have recently been strengthened by new theoretical work.
Incredibly, strong coupling involves virtual rather than real photons. Virtual photons are vacuum fluctuations associated with Heisenberg’s uncertainty principle. It is the exchange of quanta between molecules and the virtual photons inside a cavity that leads to strong coupling. Radical changes to molecular properties are thus possible by placing molecules in an optical cavity, e.g. they could be placed next to a nanostructured metal film. This simple approach is in stark contrast to existing methods of controlling the states of molecules, methods that rely on carefully sculpted ultra-short pulses of light from complex laser systems.