MATHLOCCA · Many-body Theory of Local Chemistry in Cavities

Multiple experiments have demonstrated that chemical reactivity can be modified by collectively coupling molecules to electro-magnetic vacuum-modes of a cavity. This has led to a new interdisciplinary research field, often denoted as ""polaritonic chemistry"". Despite great effort, even key underlying theoretical mechanisms are not understood today. This has recently led to controversies about fundamental origins of the observations in the collective strong coupling regime.The main goal of MATHLOCCA is to develop a first verifiable quantum many-body theory for the problem. The theory will be truly many-body, discovering new physics in molecular models with a large number of coupled electronic, nuclear, and photonic degrees of freedom. Recent breakthrough findings of the applicant will lead to an unconventional ansatz: The theory explains polaritonic chemistry without polaritons. Instead it relies on the concept of collectively modified local dark states. This ""dark state chemistry"" will explain how collective strong coupling can modify chemistry on the single-molecule level, a long-standing open question. MATHLOCCA is multi-disciplinary, discovering fundamental new quantum many-body physics in new types of electro-vibro-photonic models. This will lead to applications also in cold atom platforms.A second main objective is to introduce a new numerical theory for general open quantum many-body simulations, in terms of an entanglement optimized density matrix unravelling. The key new paradigm is to dynamically optimize the unravelling of a density matrix into pure state trajectories, making the trajectories more amenable to classical representation. This new concept will radically shift capabilities for numerical simulations in polaritonic chemistry and beyond, while giving fundamental new insight on entanglement dynamics in open quantum many-body theory.""