  A universal characterization of interactions in few- and many-body quantum
systems is often possible without detailed description of the interaction
potential, and has become a defacto assumption for cold atom research.
Universality in this context is defined as the validity to fully characterize
the system in terms of two-body scattering length. We discuss universality in
the following three contexts: closed-channel dominated Feshbach resonance,
Efimov physics near Feshbach resonances, and corrections to the mean field
energy of Bose-Einstein condensates with large scattering lengths. Novel
experimental tools and strategies are discussed to study universality in
ultracold atomic gases: dynamic control of interactions, run-away evaporative
cooling in optical traps, and preparation of few-body systems in optical
lattices.
