From single-excitation to many-body physics in disordered cold atom clouds

The interaction of light with a single atom has been explored in great detail, with optical cavities allowing one to select which and how each optical mode couples to the atom. Such setups have been used to investigate fundamental effects such as vacuum Rabi splitting to measure the light-atom coupling, the antibunching of photons, or Rabi oscillations as the atom periodically exchanges energy with the light fields.

The difficulty in venturing into the many-body case stems from the interference as the light scatters over many atoms. The light mediates a long-range dipole-dipole interaction between the particles, which stimulates a cooperative emission, as illustrated by the superradiance effect. On the other hand, Anderson localization which arises from the atomic disorder rather prevents this coupling, blocking the propagation of light. The competition between local (localized) and global (super/subradiance) effects leads to a rich physics, from the single-excitation to the many-body regime.

In this presentation, I will discuss the interaction of light with a large cloud of atoms, from the single-excitation regime where Anderson localization for light turns to be much richer than for scalar waves (acoustic, matter waves), to the several-excitation regime, where blockade and memory states can be generated through dipole-dipole interactions.