Catch the atom

Two groups have independently succeeded in confining single atoms in microscopic traps (N. Schlosser et al., Nature 411, 1024–1027; 2001, and S. Kuhr et al., Science, 14 June 2001, 10.1126/science.1062725). This feat opens the way to designing experiments in which various quantum-mechanical effects can be exploited. Several techniques already exist to manipulate individual particles, such as photons and ions, but it has been notoriously difficult to pin down neutral atoms.

The two groups developed methods to attract cooled-down atoms towards spots of high electric-field intensity in traps formed by laser beams. Schlosser et al. find that the individual rubidium atoms entering their traps scatter enough photons to image them with a CCD camera. The images show that the traps are occupied by either no atoms or just one at a time. Moreover, once an atom is caught, it can be kept trapped for up to 2 seconds — a veritable lifetime in quantum mechanics.

Kuhr et al. exerted their control over chilled caesium atoms and designed traps that can catch any desired small number of atoms. Intriguingly, they also found that these atoms can be catapulted into free flight from the trap, raising prospects of an 'atom on demand' delivery service.

As a final flourish, Schlosser et al. have positioned two traps, each containing a single atom, close to each other as shown here in the CCD image. In this set-up, the internal states of the two atoms can be intimately related to each other, or 'entangled'. Such entangled states can be used as logic elements for efficient computation tasks.