Universal Few-Body Physics

Recent Physics Today review and an article in Physics highlight the research on few-body physics in ultracold atoms.

Few-body physics is universal when inter-particle interactions are insensitive to the microscopic details of the short-range interaction potentials and can be characterized by only one or few universal parameters. In the limit of zero collision energy the two-body interactions are determined by a single parameter, the s-wave scattering length a. Universality requires a to greatly exceed the two-body potential range. This can be achieved by a resonant enhancement of a, yielding the appearance of the peculiar quantum states known as quantum halos whose wavefunction acquires long-range properties and gives rise to loosely bound states of size ~a. In the case of three interacting bosons, universality means that the three-body observables show log-periodic behavior that depends only on the scattering length a and on a three-body parameter which serve as boundary conditions for the short-range physics. Such a behavior is associated with so called Efimov physics. In a series of theoretical papers Vitaly Efimov predicted and characterized an infinite set of weakly bound triatomic states (Efimov trimers) whose binding energies (in the limit of infinit a) are related in powers of the famous universal scaling factor ~1/(22.7)2.

See publications for our recent work.