Laser Stops Bose-Einstein Cold

Michael Van Belle

Physicists at Massachusetts Institute of Technology have broken new ground in Bose-Einstein condensate research by trapping the condensate with light and tuning its behavior with magnetic fields. Both accomplishments clear the way for new work in the manipulation of ultracold atoms.
The researchers' trap relied strictly on optical forces from a laser -- in effect an optical tweezer for condensates. "Through optical means, we can confine Bose-Einstein condensates and achieve extremely precise measurements and manipulation, which was never possible using magnetic fields to insulate the condensate from the room-temperature walls of the apparatus it was formed in," said Wolfgang Ketterle, leader of the MIT team.
This limitation removed, the MIT team has confined Bose-Einstein condensates using an IR laser beam that brings the condensate into focus. "The laser creates a dipole, which is trapped in the alternating electric field of the laser beam," Ketterle said.
Although the team thought the subsequent heating of the ultracold atoms would destroy the condensate, nothing happened. "What we essentially achieved is an optical tweezer for these condensates," Ketterle said. "This tweezer, or trap, can be steered with a laser beam that is comparable in power to a common laser pointer."
Although much has to be done before ultimate control of atoms is achieved, Ketterle sees the developments as a harbinger of things to come, particularly with the atom laser, which emits atoms rather than photons.
"It's one more parameter of control. Atoms are spreading out partially because of unavoidable fuel-point energy. The atom laser has a divergency, which is basically a knob that can be used to switch off the repulsion when atoms meet. In principle, we have shown that there might be a way through an atom laser beam to control an atom's behavior," Ketterle said.