Atom-molecule coherence for ultralong-range Rydberg dimers

An important goal in quantum chemistry is the coherent control of reversible reactions between pure initial and final states of individual constituents. Recent examples of coherent control of such chemical reactions include the photoassociation of ultracold ground-state dimer molecules and of Feshbach molecules in highly excited vibrational states. Here, we extend coherent control of such reactions to the photoassociation of dimer states in highly excited electronic states. We demonstrate coherent transfer of initially free pairs of rubidium ground-state atoms to ultralong-range Rydberg molecules consisting of a highly excited Rydberg atom and a ground-state atom. The coherent evolution of the molecular system is monitored in echo and Ramsey-pulse sequences by measuring the timescales for the energy-conserving dephasing rate, T2, and for non-energy-conserving decay processes, T1. These experiments demonstrate an atom-molecule interferometer with Rydberg states.