Taking atoms for a tunnel-of-light ride.

When it comes to moving atoms from one place to another, light can lead the way.

Researchers have succeeded in getting a string of atoms to thread a hollow glass fiber by filling the tube with laser light. The resulting optical forces pull the atoms in and steer them through the fiber, even when the tube is bent.

M.J. Renn, Dana Z. Anderson, Eric A. Cornell, and their coworkers at the University of Colorado in Boulder describe their use of lasers to guide atoms along optical fibers in the Oct. 30 Physical Review Letters.

This technique offers a potentially convenient and flexible method of controlling the paths of atoms. The transparency of the optical fiber walls also allows researchers to use another laser to manipulate atoms as they travel down the tube.

"Fiber-guided atoms may facilitate many atomic physics experiments," the researchers say.

For example, at sufficiently low temperatures, atoms confined to narrow enough tubes begin to behave like waves. "This presents the exciting prospect of fiber-atomic interferometry in analogy with fiber-optic interferometry," they note.

To guide atoms along a hollow-core optical fiber, Renn and his colleagues make the laser light brightest at the tube's center and tune its frequency to a value just below that at which rubidium atoms absorb the maximum amount of light. This light enters the fiber's hollow core, glancing off the inner surface as it propagates from one end to the other.

The electric fields created inside the fiber attract atoms to the core's central region and keep them confined as they travel along the glass tube.

The Colorado team has already guided atoms in short fibers with holes as small as 10 micrometers in diameter. Guiding atoms down smaller fibers is feasible, though more challenging, the researchers say.