A submicroscopic conveyor belt can transport individual atoms as far as a centimeter, researchers report in the 14 June issue of Science Express. The breakthrough, which relies on an interaction between two opposing laser beams, may open a route toward building quantum computers out of neutral atoms.
For the past 15 years, physicists have trapped atoms with laser beams and more recently they've learned how to move them in groups. They align two overlapping and oppositely directed beams with the same frequency so that the waves' interference creates a pattern of electrical field intensities that resembles the corrugations in a washboard. The field exerts a force that pulls the neutral atoms to the high intensity peaks.
The system works well for moving several atoms at a time--although they can't count exactly how many--but isolating and transporting a few at a time is difficult, a bit like trying to carry a thimble full of water through a raging storm on a boat. And counting them is even harder. "They never knew exactly how many atoms were there," explains Harold Metcalf, a physicist at the State University of New York, Stony Brook.
Now, a team led by physicist Stefan Kuhr of Bonn University in Germany has pushed this basic technique to its highest level of precision yet, capturing and carrying a single cesium atom. One key feature is a magnetic trap, which can be opened to spit a single cesium atom into the crossed laser beams. The beam pair traps the atoms and then the team can change the frequency of one laser slightly to shift the interference pattern along the light path, carrying along the trapped cesium atoms. "We can use this as a conveyor belt to place individual atoms where we want them," Kuhr says.
A second improvement--an optical system that counts trapped atoms by measuring fluorescent light emitted by the cesium--has convinced other physicists that the team can catch a single atom. "Their results are conclusive," Metcalf says. Kuhr's next step is to place two atoms between a pair of mirrors and let them exchange photons. The simple two-atom system could become a model for the basic building blocks of a quantum computer, which uses photons to exchange information stored in single atoms.