Photon correlations and collective phenomena with Rydberg superatoms

This thesis studies the interaction of light with atom-like emitters. A common problem lies within the weak interaction of single atoms with the light field, resulting in barely measurable effects. A well-established method to circumvent this is by confining light and emitters in an optical cavity or a waveguide. However, the confinement leads to additional effects that are not present in the free space setting. Here we follow a different route and study the interaction of light with Rydberg superatoms, which possess a strong coupling to the photons without the need for confinement. A Rydberg superatom is a dense ensemble of ultra-cold atoms, excited to high principal quantum numbers. The atoms collectively interact with the light field, resulting in a strong coupling of the superatom to photons. These enhanced interactions further lead to a highly directed emission of the photons. At the same time, the Rydberg blockade prevents the ensemble from absorbing more than one photon, such that the mesoscopic superatom possesses an atom-like absorption behaviour.