A storage ring for neutral atoms

Generally, a storage ring not only stores charged particles but also defines their energy and trajectory; particles with the wrong energy simply fly away from their magnetically guided route. Neutral atoms don’t have a net charge for magnets to act on, but they can have a net magnetic dipole moment. If the atom moves slowly enough, its dipole is sufficient for magnetic guidance, and several such neutral atom guides have already been built. Physicists at Georgia Tech have now built a ring only 2 cm across, consisting of two concentric current-carrying wires, separated by 840 µm. They also built a wire “funnel” to transfer neutral rubidium atoms from a magneto-optic trap to the ring, where the atoms moved at only 85 cm/s, corresponding to kinetic energies of about 100 neV. The researchers thus dubbed their device the “Nevatron.” The image shows an atom cloud after having completed two full circuits between the two ring wires. So far, swarms of 1 million atoms have made as many as 10 circuits around the ring. The physicists are extending the work to include ring-based atom interferometry and cold-beam generation. ( J. A. Sauer , M. D. Barrett , M. S. Chapman , Phys. Rev. Lett. 87, 270401, 2001.)