Exploring the limits of light-matter coupling at the nanoscale

The interplay between light and matter encompasses a stunning spectrum of phenomena, from photosynthesis to the captivating colors of rainbows and butterfly wings. Diverse as these manifestations may be, they involve very weak light-matter coupling—in essence, light interacts with the material system but does not change its basic properties. A distinctively different set of phenomena arises, however, for systems that are artifically engineered to maximize light-matter coupling. Then intriguing quantum states can emerge that are neither light nor matter, but a hybrid of the two. Such states are of high interest from a fundamental point of view as well as for creating novel functionalities, for instance for enabling interactions between photons. The strongest couplings to date have been realized with semiconductor materials confined to tiny photonic cavities. In these devices the coupling is typically increased by making the cavity ever smaller. But even if associated fabrication challenges can be addressed, the approach is about to encounter fundamental physical limits, as a team led by Professors Giacomo Scalari and Jérôme Faist at the Institute of Quantum Electronics report in a paper published today in Nature Photonics. With this work, they set quantitative limits to the miniaturization of such nanophotonic devices.