Collision phenomena at ultra-low energies
The precision control over collisional phenomena in ultracold atomic gases has revolutionized the investigation of quantum many-body systems. In particular, the stimulating interplay between theory and experiment has led to the discovery of a variety of new quantum gases with unconventional properties. The aim of the course is to understand how quantum collisions affect the basic properties of a gas. For this purpose, a systematic introduction is given in the physics of atomic collisions at ultra-low energy. Emphasis is put on the physical picture rather than the formal theory of scattering. We discuss how atoms differ from point scatterers and how collisional types can be distinguished by introducing characteristic length scales. We explain why collisions are not only important from the kinetic point of view but also affect the stability of quantum gases. In the last part we show how collisions properties can be manipulated with the aid of a magnetic field using so-called Feshbach resonances.