Optics Seminar

Ultracold molecules are promising for many applications including quantum simulation andcontrolled chemistry, but they often suffer from rapid collisional loss, even when there areapparently no energetically accessible loss channels. Here we investigate collisions of alkalimetaldiatoms with atoms, and the effects of different types of collision complexes that canbe formed. First we consider dense and chaotic short-range collision complexes, which arethought to drive collisional loss via laser excitation. These have previously been consideredin terms of a statistically averaged effect of a dense spectrum, but we show that even for theheaviest diatom+atom systems, ultracold collisions at around 1 μK instead see the effects ofindividual states; the corresponding features in the scattering are very broad on anexperimental scale. In a second study we analyze a large set of experimentally observedmagnetic Feshbach resonances for NaK+K. We conclude that they are not members of thechaotic bath of short-range states discussed in the first part of this talk. Instead, they are mostlikely simple long-range states with the character of the separated atom and molecule. Thesetwo studies highlight contrasting aspects of ultracold atom+diatom scattering and bring uscloser to understanding and ultimately harnessing ultracold molecular collisions.