By and large, physicists have succeeded in their quest to tame the atom. These days, atoms can be laser cooled to their ground states, stored in traps for minutes, and switched between internal states virtually at will. (See the article by Ignacio Cirac and Peter Zoller in Physics Today, March 2004, page 38.)
Molecules, however, are wilder beasts. They are all but impervious to laser cooling, which demands a closed optical loop—that is, a sequence of photoexcitation and decay that can be repeated ad infinitum. Due to the additional degrees of freedom afforded by rotational and vibrational modes, molecules tend to decay unpredictably, often to states that can’t be optically addressed. Inevitably, the loop breaks.
Over the years, experimenters have devised strategies to overcome the optical-loop problem: creating cold molecules in situ from cold, trapped clouds of reactive atoms (see the article by Debbie Jin and Jun Ye,...
