Monitoring energy flow in light-matter states

When a molecule is embedded inside a nanocavity and under certain conditions, new hybrid matter-light states appear, called polaritons. They result from the energy exchange between the optical field inside the nanocavity and the embedded molecules, similar to two coupled pendula exchanging energy.

This leads to changes in the optical properties of the resonator-molecule system. By engineering the properties of the optical field via the nanocavity design, and the way light couples to it, the properties and behavior of “polaritonic systems” can be modified at will and in a systematic fashion.

The energy flow between polaritonic states is crucial to understand for a wide range of applications. In a new article published in Communications Physics, the lab of Majed Chergui at EPFL within the Lausanne Centre for Ultrafast Science, in collaboration with the group of Karl Börjesson at the University of Gothenburg, has managed to gain unique new insights into the energy flow between light-matter states that are created when molecular excitations are coupled to an optical field.

The international team shows how excitation into the energetically higher-lying polaritonic state leads to population of the lowest within tens of femtoseconds. To achieve these results, the authors used state-of-the-art visible multidimensional spectroscopy (an optical domain analogue of nuclear magnetic resonance spectroscopy), which allows to overcome the typically encountered uncertainty between time and energy resolution in spectroscopy and is uniquely suited to study these light-matter interactions. These results demonstrate the ability to engineer light-matter states at will and to control the way energy flows in them. The team’s novel results are deemed to stimulate future experiments on similar systems and contribute to the development of novel applications.