Quantum dynamics methods for fluctuating systems in quantum environments: Development and application

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Seogjoo J. Jang of Queens College, City University of New York, is supported by an award from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry for developing and applying quantum dynamics methods for fluctuating systems in quantum environments. For example, think of a molecular substance, like sugar, dissolved in a glass of water. One could think of the electrons in the sugar molecule as the quantum system and the vibrations of the atoms in the sugar molecule as the quantum environment. The fluctuations are caused by the motions of the solvent molecules. Because of the counter-intuitive nature of quantum mechanics, it can be difficult to predict or understand the behavior of quantum systems without elaborate calculations. However, even after almost a century since the theory of quantum mechanics was founded, reliable quantum dynamics calculations beyond simple models and systems remain notoriously difficult to solve. Building on their earlier computational research, Professor Jang and coworkers are establishing systematic computational approaches appropriate for very large systems in realistic environments. Accurate descriptions of the dynamic behaviors of such quantum systems has significant implications for designing novel energy conversions, imaging, and information processing devices. Applications of these methods can elucidate quantum effects that remain important in noisy environments and can help develop new kinds of novel quantum devices. Professor Jang is working on a book on molecular excitons, which are important for solar energy conversion and imaging, and a review article on quantum dynamics methods. He is also dedicated to organizing conferences on cutting edge topics, and is developing new types of undergraduate level classes integrating experiments and computation.Professor Jang's group is developing and applying theories and computational methods for the dynamics calculation of quantum systems subject to general time dependent fluctuations while interacting with quantum environments. Accurate descriptions of the interplay of these two complicating factors has significant implications for long-range energy and charge transfer processes in complex molecular environments, and is one of central issues in quantum thermodynamics, information processing, and conductance. On one hand, this theory is pursued through master equation approaches, by combining the polaron transformation or modular coarse-graining with systematic higher order expansions. On the other hand, path-integral based theories and simulation methods are generalized for fluctuating systems. These methods are then applied and tested for the dynamics of delocalized excitons in light harvesting complexes and nanotubes, and for proton or proton-coupled electron transfer reactions in dynamic molecular environments. Outcomes of this research can elucidate spatio-temporal dynamics of delocalized excitons in complex environments and can provide key insights into the interplay between the effects of quantum environments and time dependent fluctuations in the dynamics of protons and loose electrons Professor Jang is working on a book on the dynamics of molecular excitons and a comprehensive review article on quantum master and Fokker-Planck equations. He continues organizing conferences and workshops on topical issues such as excitons, quantum information, machine learning, and chemical sensing, and is also designing new small group chemistry courses that can integrate experiments and computation/modeling.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.