Number 235 (Story #1), July 28, 1995 by Phillip F. Schewe and Ben Stein|
A MAGNETIC MIRROR FOR CHILLY ATOMS has been demonstrated, allowing researchers to manipulate cold atoms in a new way, and possibly bringing about a novel method for exploring the wavelike nature of atoms. Edward Hinds (203-432-3826) and his coworkers at Yale built their mirror using a commonplace material: strips of audio tape recorded with a sinusoidally varying magnetic field pattern. A supply of atoms--a rubidium-85 gas--is trapped and cooled with a combination of laser light and magnetic fields in a configuration similar to that used to create Bose-Einstein condensation (Update 233). The magneto-optic trap not only helps to cool the atoms but also orients the atoms' magnetic moments (the atoms can be thought of as tiny bar magnets). Cooled to a temperature of about 30 millionths of a degree above absolute zero, the atoms are then dropped onto the tape from a height of one inch. The magnetic interaction between the atom and the tiny domains in the tape causes the atoms to bounce back up in an orderly way. In fact, the atoms can bounce repeatedly (or even be recaptured in the trap). Such mirrors are needed for carrying out "atom optics," the manipulation of atoms just as light waves are manipulated by lenses and mirrors in conventional optics. Unlike a previously demonstrated atom mirror (Update 149), the Yale mirror does not use laser light to reflect the atoms. (T.M. Roach et al, Physical Review Letters, 24 July 1995.) At a June laser spectroscopy meeting in Capri, Italy, Hinds announced that the Yale team is now using a new medium for magnetic mirrors, floppy disks, from which they made a converging mirror. The researchers sealed the disk across the open end of a tube, and evacuated the air from the tube. The suction made the disk bow inward, forming a concave surface able to focus reflected atoms into a single point. Future possibilities also include using magnetic mirrors to construct a "reflection grating" for atoms in order to study their wavelike properties.