Sticky collisions

Ultracold molecules can be stable against chemical reactions, yet experiments have found that they can still be lost when they collide. What causes this loss? One intriguing possibility is that two molecules undergo "sticky collisions"; At ultracold temperatures they can form unusually long-lived collision complexes, which perhaps mediate the loss. This raises the question what happens microscopically during these collisions and how the complex is ultimately lost.

We develop theory to study these long-lived collision complexes and explore their possible role by exotic processes such as photo-excitation by the trapping laser. Subsequent experiments have observed sticking and trap-photo-chemistry in semi-quantitative agreement with our predictions. Other experimental observations remain unexplained, and the microscopic origin of collisional loss is not yet fully understood. Understanding what happens when ultracold molecules collide - and how this loss can be controlled - remains an active research direction.