Exploring Ultracold Matter Along the Complexity Axis

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Placing ordinary matter in extraordinary circumstances can create fascinating new phenomena and applications in physics. For example, it was realized some time ago that certain gases could be reduced to temperatures just a tiny bit above absolute zero, but without condensing into liquid drops. This new discipline of "ultracold" gases has led to a wealth of new understanding of quantum mechanical behavior of collections of simple atoms. Now, a new set of experiments seeks to enrich this discipline by introducing atoms and molecules with internal complexity. Doing so will lead to unprecedented detail in understanding and controlling chemical reactions, with applications yet to be dreamed of. Amazingly, it will in certain cases also allow for a deeper understanding of the fundamental rules of the universe than even the largest particle accelerator can provide. To carry out such experiments, it is necessary to thoroughly understand the dynamics of a complex, ultracold gas. This work will explore the role of complexity in the gas, considering phenomena such as basic thermodynamics, in which the propagation of heat or of sound can be different in different directions, or may depend on (and thus reveal) chemical reactivity. It will also consider the possibility, conjectured but not yet demonstrated, that molecules in the gas can stick to each other for brief amounts of time. Properties of this self-adhesive gas must be thoroughly understood before ultracold gases can be harnessed for applications. To do so, the work will investigate in detail the role of quantum chaos in the two-body collision dynamics. Chaos has already been demonstrated, or at least suspected, in ultracold collisions of lanthanide dimer atoms as well as alkali dimer molecules. The first steps have been taken, but a complete analysis, including the statistical distributions of energy levels and resonance widths, as well as the influence of magnetic fields, must still be undertaken. This analysis will be carried out using models of various degrees of complexity, to reveal the essential physics of the phenomena. Moreover, while the differential scattering cross sections of dipolar atoms and molecules are known, their complete influence on the thermodynamics of the gas remains largely unexplored. Dynamics of an ultracold dipolar gas will be undertaken, using Monte Carlo calculations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.