Quantum Theories of Atomic and Molecular Interactions and their Applications

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Since the world is made of atoms, it is not surprising that most of the important questions in science and technology can be put under the category of understanding a few-atom or a many-atom quantum system. This includes both the "big questions" such as the origin of life, and the more practical questions such as the everyday chemistry, biology, and medicine. While this atomic picture of the world is sound and natural, its implementation at the quantum level is so difficult that it has barely started. Both the brute-force approach of quantum chemistry and the often-over-simplified models of quantum many-body theory have key limitations with no clear path towards resolution. While some scientists are starting to pin their hopes on a future quantum computer, computation alone, even when realized, never brings the true understanding that has always been the symbol and the aspiration of science. This project is a part of a long-term program that intends to develop a new theoretical framework for the atomic picture of the world at the quantum level. It is from the perspective of atomic and molecular physics and is based on new and most efficient characterization of atomic interactions. The theory hopes to enable systematic understanding of complex quantum systems that are impossible to treat in the quantum chemistry approach and capture much essential physics that has been missing from simplified many-body models.The foundation of the proposed framework is a new effective theory of atomic interactions, to be developed as a part of this project. It is a substantial generalization of the more traditional quantum defect theories, previously developed and formulated mostly for single-scale isotropic interaction potentials, to electromagnetic interactions of all types including anisotropic potentials and potentials with multiple length scales. This is one of the key ingredients that will enable the quantitative understanding of atom-molecule and molecule-molecule interactions, which are both where quantum complexity first emerges and the foundation for the understanding of more complex quantum systems made of more atoms and/or molecules.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.