Grant: Discovery Grants Program - Individual

Funding is requested for a theoretical research program that will explore quantum dynamics of binary, few-body and many-body molecular systems in electromagnetic fields. Specifically, the proposed research will be on three topics: (i) low-temperature dynamics of complex polyatomic molecules and controlled chemistry; (ii) polarons in new interaction regimes; and (iii) controlled energy transfer in open quantum systems. Within each of these topics, we will address the most pressing questions at the forefront of current research in physics and chemistry and only consider molecular systems that have been or can soon be experimentally realized. **The goal of research direction (i) will be to study the feasibility of buffer gas cooling of hydrocarbon molecules to subKelvin temperatures and to develop tools to explore the unique features of bimolecular chemical reactions of cold molecules in electromagnetic fields. This work will be closely related with the experiments on buffer gas cooling of molecules, an emerging research direction aiming to create new technologies for sensitive detection of trace molecules and the production of high-flux beams of polyatomic molecules slowly moving in the laboratory frame. **The research of topics (ii) and (iii) is motivated by the spectacular recent experiments which demonstrated the possibility of synthesizing molecules at temperatures below 1 microKelvin. It was found that ultracold molecules can be very reactive, undergoing chemical reactions at fast rates. It was also demonstrated that ultracold molecules can be trapped in a periodic potential of an optical lattice. Current experiments are focused on improving the trapping fidelity to minimize the effect of disorder, in an effort to produce a periodic, crystal-like system, where molecules are suspended by the laser field potential and intermolecular interactions can be controlled by electromagnetic fields. **We will study the realization of the polaron Hamiltonians with molecules trapped in laser fields. Polarons are quasi-particles appearing in the excitation spectra of particles (such as electrons or excitons) coupled to a bosonic field (such as phonons). We will calculate the phase diagram of polarons in the previously unexplored range of particle - field interaction parameters and study the possibility of observing non-linear polaron interactions in the excitation spectra of cold molecules. We will develop computer codes to study the feasibility of the experimental realization of controlled open quantum systems with molecules trapped in optical lattices. The goal will be to propose an experimental system that could be used to study (a) the dynamics of quantum particles coupled to a finite-size bath near a transition between the Markovian and non-Markovian environment; and (b) control mechanisms of energy transport in open quantum systems with controllable, finite-size baths. **If our results show that complex organic molecules can be cooled to ultracold temperatures, the research field of cold molecules will greatly expand. Within reach will be the possibility to study tunnelling reactions of biological interest without thermal averaging as well as many fundamental phenomena that cannot yet be studied. Examples include effects of the geometric phase and tunable resonances in chemical dynamics, effects of fine structure on chemical transformations and the role of quantum statistics, or lack thereof, in chemical reactivity. Our study of novel polaron problems will connect molecular spectroscopy and condensed-matter physics in new ways, providing a new stimulus to both research fields. The realization of controllable open systems with trapped molecules may become a new paradigm in the study of few-particle dynamics under dissipation.