Chemical reactions at ultracold temperatures are expected to be dominated byquantum mechanical effects. Although progress towards ultracold chemistry hasbeen made through atomic photoassociation, Feshbach resonances and bimolecularcollisions, these approaches have been limited by imperfect quantum stateselectivity. In particular, attaining complete control of the ground or excitedcontinuum quantum states has remained a challenge. Here we achieve this controlusing photodissociation, an approach that encodes a wealth of information inthe angular distribution of outgoing fragments. By photodissociating ultracold88Sr2 molecules with full control of the low-energy continuum, we access thequantum regime of ultracold chemistry, observing resonant and nonresonantbarrier tunneling, matter-wave interference of reaction products and forbiddenreaction pathways. Our results illustrate the failure of the traditionalquasiclassical model of photodissociation and instead are accurately describedby a quantum mechanical model. The experimental ability to produce well-definedquantum continuum states at low energies will enable high-precision studies oflong-range molecular potentials for which accurate quantum chemistry models areunavailable, and may serve as a source of entangled states and coherent matterwaves for a wide range of experiments in quantum optics.
展开▼
