The Quantum and Classical Sides of a Chemical Reaction

Flasks and hotplates are too crude for ultracold chemists. Instead, they drive forward chemical reactions with lasers, which are used to control the quantum states of individual atoms and molecules at temperatures close to absolute zero. Tanya Zelevinsky and colleagues at Columbia University have now used this precision approach to determine when a simple reaction—the dissociation of a diatomic molecule—should be described quantum mechanically and when it should be described (somewhat) classically.