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Ultracold matter

Ultracold matter

Molecular storage ring makes its debut

01 Jul 2001

For almost two decades laser radiation has been used first to slow, then to cool and finally to trap atoms. But until now, there has been no technique to do the same for molecules.

The multitude of energy levels found in molecules has so far defeated the use of laser-based techniques, which rely on exciting transitions that can spontaneously radiate and return to the original levels. Many other ingenious methods have been invented to slow, cool or trap molecules. Paramagnetic molecules have been cooled to sub-kelvin temperatures in a cold helium buffer gas and then magnetically trapped. Ultracold alkali molecules have been formed by the photoassociation (the reverse of photodissociation) of trapped ultracold atoms. What is missing, however, is a single technique for slowing, cooling and trapping any species of molecule.

Now Gerard Meijer and co-workers at the University of Nijmegen and the FOM Institute for Plasma Physics in the Netherlands have taken an important step towards this goal by developing a device that slows and confines polar molecules (F Crompvoets et al. 2001 Nature 411 174). They recently slowed bunches of deuterated ammonia molecules (ND3) from 275 m s-1 to 80 m s-1, and then confined them in a storage ring about the size of a dinner plate.

In the July issue of Physics World, Harvey Gould of Lawrence Berkeley National Laboratory, USA, examines the state-of-the-art in molecular storage and speculates where it may lead.

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