title: Universality in three- and four-body bound states of ultracold atoms.
abstract: Under certain circumstances, three or more interacting particles may form bound states. Although the general few-body problem is not analytically solvable, the so-called Efimov trimers appear for a system of three particles with resonant two-body interactions. The binding energies of these trimers are predicted to be universally connected to each other, independent of the microscopic details of the interaction. By exploiting a Feshbach resonance to widely tune the interactions between trapped ultracold lithium atoms, we find evidence for two universally connected Efimov trimers and their associated four-body bound states. A total of 11 precisely determined three- and four-body features are found in the inelastic-loss spectrum. Their relative locations on either side of the resonance agree well with universal theory, whereas a systematic deviation from universality is found when comparing features across the resonance.
authors: Department of Physics and Astronomy and Rice Quantum Institute, Rice University, Houston, TX 77005, USA. scott.pollack@rice.edu
authors: Scott E
authors: SE
authors: Pollack
authors: Daniel
authors: D
authors: Dries
authors: Randall G
authors: RG
authors: Hulet