Chilling an atom in solitary confinement.

Chilling an atom in solitary confinement 

Just as human behavior can turn into a soap opera as the number of participants increases, atom behavior gets more complicated as the atomic crowd grows. Seeking a clearer understanding of how atoms behave, some scientists isolate individual atoms and try to calm their normally dizzying motions to a standstill (SN: 6/21/86, p.388).

Isolating atoms and rendering them motionless might lead to more precise atomic clocks and better satellite navigational systems, researchers say.

Physicists at the University of Washington in Seattle now propose a way of isolating electrically charged barium atoms and completely stopping the frenetic twirls and vibrations these ions normally perform at room temperature and pressure. Eventually, they hope to monitor how stilled, solitary atoms respond to probes such as precise jolts of energy from lasers.

So far the group has succeeded in isolating single ions for up to four days but has yet to cool them to a motionless state, says Warren Nagourney, who works on the project with Hans Dehmelt and Nan Yu. As the barium ion relaxes to lower energy states, it emits photons in the visible region of the electromagnetic spectrum. "You can see the atom blinking," notes Nagourney, who describes the experiment in the August PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES (Vol.86, No.15).

Earlier this year, four other physicists became the first to trap single mercury ions and cool them in this way to about 50 millionths of a kelvin above absolute zero, the coldest and stillest an atom can be. "These [two] experiments are very similar," says David J. Wineland, who led the effort at the National Institute of Standards and Technology in Boulder, Colo.

Nagourney concurs but says his group will use a modified ion trap (now undergoing initial tests), which cancels stray electrical fields that otherwise gently jostle a confined atom, and a novel method of verifying that the trapped ion actually cools to absolute zero.

Both teams use an electric field oscillating at radio frequencies to trap individual ions within a metal loop enclosed in a near-perfect vacuum. In a back-of-the-envelope calculation, Nagourney estimates that the distance between the confined ion and atoms outside the loop is analogous to the distance between a person in Boston and one in Washington, D.C. Even so, the ion performs a lively dance, which scientists quell with a laser that makes the ion absorb and reemit photons, each of which carries away a bit of the ion's energy (SN: 7/23/88, p.52).