"Making hot atoms interact:
The research and the spectroscopy of hot vapors carry great potential, ranging from fundamental research to robust applications in the context of quantum technologies. Although spectroscopy of atomic and molecular gases is known since Gustav Robert Kirchhoff’s times recent developments in cell engineering, laser technology and electronics opens the field to new and surprising research activities. In this talk I will focus on optical non-linearities induced by atom-atom interactions, either by highly excited Rydberg states or for low lying states via the resonant dipole-dipole interaction. These non-linearities are manifest at the single photon level and can be exploited to generate and process quantum states of light fields. As a platform we us a variety of cell types and excitation schemes, where the most advanced ones involve integrated photonic waveguides, micro-resonators and/or Rydberg states.