Abstract
The following two lectures deal with diffusion resonances, and more specifically with Fano-Feshbach resonances. These are an essential tool in quantum gas physics, paving the way for the regime of strong interactions, which is reached when the diffusion length becomes of the order of the distance between particles in the gas. They also make it possible to prepare gases with near-zero interaction (a=0), thus realizing the perfect gas model. They are also a source of highly accurate data on dimer structure and thus on interatomic potentials. Finally, they have enabled the development of highly original research into few-body systems, including the study of Efimov states.
