Observation of Resonant Monopole-Dipole Energy Transfer between Rydberg Atoms and Polar Molecules

Resonant energy transfer (RET) between the equal parity 1s65s ^{3}S_{1} and 1s66s ^{3}S_{1} Rydberg levels in helium has been observed in low-temperature (∼80  mK) collisions with ammonia molecules that undergo inversion transitions in their X ^{1}A_{1} ground electronic state. This hybrid Rydberg-atom-polar-molecule resonant energy transfer represents a monopole-dipole energy exchange reaction that necessarily requires spatial overlap of the Rydberg-electron and molecular wave functions. Calculations that account explicitly for the charge-dipole interaction between the Rydberg electron and the molecule provide a quantitative explanation of the observations. Total parity is conserved in the reaction through the mixing of collisional angular momentum in the atom-molecule complex. This work opens opportunities to expand the toolbox for quantum science with charge-dipole-mediated energy exchange in hybrid atom-polar-molecule platforms.