Condensed Matter + Quantum light = QED materials

An important goal of modern condensed-matter physics involves the search for states of matter with emergent properties and desirable functionalities. In particular, the hunt for new materials that show strong light-matter interaction is a very active field. When the interaction is enhanced to be stronger than the dissipation of light and matter entities, typically by embedding materials into optical microcavities (QED regime), one approaches the ultra-strong coupling regime resulting in the formation of hybrid half-light half-matter bosonic quasiparticles called microcavity polaritons. Ultra-strong quantum light–matter interaction, which goes beyond weak and strong coupling to make the coupling strength comparable to the transition frequencies in the matter system has, in the last 2 decades, evolved from a theoretical idea to an experimental reality. These achievements have led to increased control of quantum systems and to applications such as lasers, quantum sensing and quantum information processing.

In this talk, we review the state of the art of cavity platforms and highlight recent theoretical proposals and first experimental demonstrations of cavity control of collective phenomena in quantum materials such as cavity superconductivity, cavity phononics and ferroelectricity, light–magnon coupling and cavity quantum Hall effect. Finally, some recent theoretical results from our group about cavity topological matter systems will be outlined.