Ultracold Few-Body Systems

Recent advances in controlling interatomic interactions, coupled with new techniques for producing and interrogating exotic regimes in ultracold quantum gases, have resulted in the emergence of ultracold systems as a natural and inspiring playground for few-body physics, feeding the robust and interdisciplinary growth of this field. Both theory and experiment have benefitted from this interplay and have pushed the study of fundamental, universal few-body physics forward more rapidly than at any time during the previous few decades. The non-pertubative nature of these strongly correlated few-body systems makes them extremely challenging, but at the same time is responsible for interesting and counterintuitive phenomena the Efimov effect being one of the most prominent examples. In this paper, we review the fundamentals of strongly correlated few-body physics for ultracold systems, much of which is related to three-body Efimov physics, and we survey the current state of experimental achievement. We do not, however, restrict our exploration to the three-body Efimov effect and analyze several few-body systems that fall outside this now-canonical Efimov scenario. We discuss systems with more than three particles a natural extension of Efimov physics and we discuss systems in which the interactions are not short-ranged, therefore violating a fundamental condition for Efimov physics, but with equally universal properties.