Control of reactive collisions by quantum interference

In this study, we achieved magnetic control of reactive scattering in an ultracold mixture of 23Na atoms and 23Na6Li molecules. In most molecular collisions, particles react or are lost near short range with unity probability, leading to the so-called universal rate. By contrast, the Na + NaLi system was shown to have only ~4% loss probability in a fully spin-polarized state. By controlling the phase of the scattering wave function via a Feshbach resonance, we modified the loss rate by more than a factor of 100, from far below to far above the universal limit. The results are explained in analogy with an optical Fabry-Perot resonator by interference of reflections at short and long range. Our work demonstrates quantum control of chemistry by magnetic fields with the full dynamic range predicted by our models. Description Magnetic control of chemistry There is a considerable interest in realizing control of molecular reactions at ultracold temperatures because of unprecedented opportunities in the ultimate quantum regime. Son et al. discovered an ideal system, a sodium atom and a sodium–lithium molecule, in which the combination of Feshbach resonances and low short-range loss probability allows for the significant suppression or enhancement of reactive collisions, controlled by external magnetic fields (see the Perspective by Cornish and Hutson). This work presents a method for manipulating the reactivity of ultracold molecules that is qualitatively different from previous experiments. At the same time, this method is highly dependent on the distinctive short-range properties offered by the sodium/sodium–lithium complex and is subject to further testing in other systems. —YS Short-range properties of Na–NaLi enable precise control of chemical reactivity using magnetic fields and quantum interference.