Why Are Cold Molecules So Hot?

Abstract

The development of techniques to cool/slow and trap atoms and molecules brought about a revolution in atomic and molecular physics, with an impact on physics in large. When slowed/cooled down, atoms and molecules become matter waves whose properties differ vastly from those of thermal matter. In particular, close to absolute zero temperature, the interaction range of atoms or molecules increases far beyond their dimensions, imparting to them highly desirable collective and collisional properties. The latter have been predicted to give rise to a novel ultracold chemistry. The article describes the main techniques of producing cold molecules, both the indirect ones (photoassociation of cold atoms, collisional association of cold atoms controlled via Feshbach resonances) and the direct techniques (buffer-gas cooling, Stark deceleration and others). Ongoing and anticipated future experiments with cold molecules are reviewed, including pioneering ventures aimed at radiative lifetime measurements, reduction of transit time broadening, measurements of ultracold collisional cross-sections, and testing of fundamental symmetries in nature, such as the time-reversal symmetry and parity.