Controlling ultracold molecular reactions through nuclear spins

Controlling the quantum states of reactive systems has enabled the study of underlying interaction potentials and the alteration of reaction rates. However, control over the quantum states of reaction outcomes has remained challenging. In this talk, I discuss our recent work which utilizes the nuclear spin states of ultracold KRb reactant molecules prepared in their rovibronic ground state to control the quantum states of products formed through the reaction 2KRb → K₂ + Rb₂. This newly demonstrated form of control relies on the conservation of nuclear spin throughout the reaction. [Nat. Chem. https://doi.org/10.1038/s41557-020-00610-0 (2020)] Specifically, by performing resonance-enhanced multiphoton ionization spectroscopy, we find that the products retain the reactants’ nuclear spins almost perfectly, which is manifested as a strong parity preference for the rotational quantum states of the products. By applying an external magnetic field to change the initial nuclear spin state of the reactants, we then observe that the relative population in different product quantum states can be altered. These techniques could enable the study of quantum entanglement between reaction products.