Atoms on a Wire

Physicists have coaxed ultracold atoms to migrate along the outside of a wire by sending a current through it, opening a new way to move such atoms around. The technique, to be described in the 8 March Physical Review Letters, could be used to manipulate atoms in small nanostructures in the same versatile ways as electrons whiz around integrated circuits. Ultimately such "atom optics" might even help make components for quantum computers.

It's not easy to manipulate individual atoms. First, you must confine them in an magneto-optical trap--a device that confines a small cloud of atoms in a magnetic field and cools them down to almost absolute zero. Only two tricks have been feasible so far for moving atoms around after they have been caged: tweak the magnetic field, or allow them to drop under gravity. Now, experimental physicist Jörg Schmiedmayer and his colleagues at Innsbruck University in Austria have demonstrated a new addition to the toolbox of atom opticians: current-carrying wires that can "guide" atoms just as optical fibers transmit light.

The current sets up a magnetic field that attracts the small magnetic fields of the atoms. Because of its quantum properties, the atom's magnetic field can align itself with or against the wire's magnetic field. When the magnetic fields were opposite, Schmiedmayer observed atoms moving toward the wire. This attraction also steered them down the wire. To guide atoms with magnetic fields parallel to that of the wire, the researchers superimposed an additional magnetic field on the wire. This created a sort of tunnel along one side in which the magnetic field was minimized. In this "side wire" approach, the atoms entered the tunnel to escape the wire's repellent magnetic field. The team snapped charge-coupled device camera pictures of the atoms moving along the wire by briefly illuminating them with the lasers.

Schmiedmayer envisions applications resembling integrated circuits in electronics, ones that might be used for quantum computation. "You could mount the side-guide wire on a surface and use nanofabrication technology to produce very small wires and structures," he says. "In fact, we are trying to make such small structures now."

This research is a "step in the right direction" toward the creation of integrated atom optics, says physicist Wolfgang Ketterle of the Massachusetts Institute of Technology. He also thinks that wires may have advantages as magnetic traps for atoms over the more bulky systems now in use.