Engineering Polyatomic Molecules with Optical Cycling Centers for Quantum Science Applications

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Laser cooling and trapping of atoms has revolutionized atomic and molecular physics and led to breakthroughs in several disciplines of science and technology. The advances enabled a novel generation of atomic clocks, simulation of exotic phases of matter, the development of highly-sensitive sensors, and atom-based quantum information science. Laser cooling of atoms has also made possible the assembly of ultracold, sub microkelvin diatomic molecular samples that are sufficiently dense for quantum degeneracy effects to be important. These molecules are confined by electric and magnetic fields as well as optical traps or tweezers, where they are isolated from their environment and can be carefully studied. Achieving similar control with larger polyatomic molecules remains challenging. Such molecules have more complex electronic, vibrational, and bending motion into which energy can be inadvertently transferred. It is then far from obvious whether there exist polyatomic molecules with a nearly-closed optical cycling transition needed for successful laser cooling. These transitions can then repeatedly scatter photons so that the molecular center-of-mass motion can be cooled below a milli-Kelvin or less equivalent kinetic energy. A list of promising applications unique to polyatomic molecules does exist. This includes performing precision spectroscopy to test the Standard Model of particle physics, and, excitingly, the promise of quantum control of chemical reactions as each ultracold molecule can be prepared in a unique vibrational state. As the de-Broglie wavelength of the molecules is much larger than the range of intermolecular forces, the dynamics of the breaking and making chemical bonds promises to be even more interesting.This project will improve understanding of the electronic and vibrational structure of the "relatively-simple" triatomic molecules M-OH, where the metal-cation M is an alkaline-earth or rare-earth atom. They have a usable optical cycling transition located on the metal cation. The researchers will then study the effect of replacing the hydrogen atom in M-OH by a larger ligand or chains of molecules. Adding alkaline-earth or rare-earth atoms with their cycling transitions to prospective polyatomic molecules is another research direction. In either approach the valence electron of the metal-cation should not be significantly disturbed, and optical cycling and cooling might remain possible. The ultimate dream is to design polyatomic molecules with more than one optical cycling center. Scientifically, the research will advance understanding of metal-ligand couplings and elucidate the role of molecular complexity on the diagonal character of Franck-Condon factors, the quantitative measure for the quality of optical cycling transitions. The shape of potential energy surfaces will be characterized for atomic geometries, where all atoms are close to each other and, when feasible, where one of more atoms has dissociated and is far away. The researchers will locate their minima, saddle points as well as conical intersections, where two potential surfaces of the same electron symmetry touch. Renner-Teller effects will also be studied for the M-OH trimer near linear geometries. This work is jointly supported by the Theoretical Atomic, Molecular and Optical Physics Program and the Quantum Information Science Program within the Division of Physics, as well as by the Chemical Theory, Models and Computational Methods Program in the Division of Chemistry.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.