A theoretical investigation of few-body systems

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Few-body collisions are playing an increasingly important role in experiments on ultracold quantum gases. This work addresses some of the most important outstanding questions about such collisions: What happens when three bodies collide in the reduced dimensions of an optical lattice? What happens when four bodies collide? What, if any, is the role of Efimov physics in these collisions? Recent theoretical progress suggests that Efimov physics underlies most ultracold three-body collisions, determining the dependence of the associated elastic and inelastic rate coefficients on energy, mass, and scattering length. Extending this understanding to answer these open questions is the focus of this work. Given the importance of few-body collisions in ultracold experiments, gaining a more complete theoretical understanding is essential. Theoretical input can help both in the design of better experiments and in interpreting what has been measured. Ultracold experiments in optical lattices - and thus in reduced dimensions - are becoming especially important for potential technological applications of ultracold atom physics. By interacting with experimentalists and answering the questions important for them, this work can thus advance the broader efforts in ultracold physics. Even more broadly, few-body physics lies at the overlap of atomic, chemical, and nuclear physics. For instance, the process of three-body recombination, where three free atoms collide to form a diatomic molecule, is one of the simplest reactions that forms molecules from atoms. They thus play an important role in the chemistry of interstellar clouds and planetary atmospheres. At higher temperatures, these reactions also become important for combustion.