Universal four-body resonances in ultracold atomic and molecular gases

We study the manifestations of universal four-body physics in ultracold, strongly interacting, atomic and molecular gases. We find that ultracold scattering observables such as four-body recombination and dimer-dimer relaxation, display resonant structure caused by the emergence of universal four-boson states. Such resonant effects enable the control of few-body interactions and potentially enrich the range of experimentally accessible phenomena. We also demonstrate the close relationship between universal four-body physics with Efimov physics. Our analysis shows that $B_{2}+B_{2}\rightarrow B_{3}+B$ rearrangement reactions offers a path for an efficient trimer formation, building the bridge between three- and four-body universal physics. Our analysis of the temperature dependence of this reaction provides an interpretation of the available experimental data and sheds light on the possible experimental realization of rearrangement processes in ultracold gases. This work was supported by the National Science Foundation.