Quantum encounters of the cold kind

Since the introduction of laser-cooling techniques for neutral atoms in the early 1980s, the study of collisional interactions between atoms and molecules has been extended to the regime of ultracold temperatures. With nanokelvin temperatures now attainable, our ability to probe the interactions, both experimentally and theoretically, has also progressed. Understanding of the subtle and often highly quantum-mechanical effects that are manifest at such low energies has advanced to the point where new precision measurements are matched by highly accurate theoretical calculations. Low-energy phenomena such as Bose-Einstein condensation and the photoassociation of atoms into bound molecules are now accurately described with no free parameters.