It was long considered a practical impossibility to extend the methods of laser cooling and trapping to diatomic molecules. Here, unlike in atoms, photon absorption can excite internal degrees of freedom (vibration and rotation), which both interrupts the optical cycling needed for motional cooling and leads to internal-state heating. We have recently demonstrated that, nevertheless, methods like those of standard atomic laser cooling and trapping can be applied to some molecules. We have achieved sub-Doppler cooling in 1-D, radiation pressure slowing and stopping of a molecular beam, and 3-D magneto-optical trapping of SrF molecules. This promises to open a wide range of scientific applications from precision measurements, to quantum information and quantum simulation, to precise control over chemical reactions.
David DeMille, Professor of Physics, Yale University