Abstract
WHAT do you get if you cross light with matter? It is a question that fascinates today's researchers in quantum optoelectronics, who want to see how far the physical states of the world can be intertwined. Although we have a good understanding of the quantum ingredients of optics and solids – photons and atoms – it turns out that assembling these building blocks in deliberately unfamiliar ways can lead to what is new and often quite unexpected behaviour.