It’s the Atomic Air Force! Bizzare behavior startles scientists


Feb 06, 2006

PHYSICISTS at the U.S. Department of Commerce’s National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder (CU-Boulder) report the first sighting of atoms flying in formation. While a conventional aircraft-based air force and geese usually prefer a classic “V” formation, strontium atoms observed in an experiment with precision laser pulses and ultra-cold temperatures were recorded flying in the shape of a cube.

“This really bizarre behavior is believed to occur with all atoms under similar conditions,” says physicist Jun Ye of NIST, who led the research at JILA, a joint institute of NIST and CU-Boulder. “Atoms have not previously been seen flying in formation.”

The experiment was conducted with a dense gaseous cloud of 100 million strontium atoms. The atoms were held in a vacuum chamber with a magnetic field and six intersecting laser beams. The atoms, usually at a very hot 800 Kelvin (980 ºF), were trapped with the magnetic field and blue laser light, and cooled to 1 milliKelvin. Then, with red laser light, the atoms were rapidly cooled further to about 250 nanoKelvin, which is almost absolute zero, or -459 ºF.

The magnetic field then was turned off, and the red laser beams were tuned to a slightly higher frequency than strontium’s weak, red resonance frequency. This caused the atoms to fly apart in cubic formation. The flying structure, say the scientists, was created in part by a recoil effect. This was the momentum kick received by the atoms as they absorbed or emitted each particle of light, or photon. This effect is similar to the recoil received when shooting a gun, Ye says. The combined effect of the six incident beams makes the atoms fly away in cube-shaped clusters. The research team captured images of the atoms flying in clusters at speeds of about 10-15 cm/sec.


Strontium atoms form a “cube” pattern as the frequency of laser light used to manipulate them changes. (Left) Atoms become visible at the eight corners of a cube. (Middle) Atoms also appear at the midpoints of the lines forming each cube face and begin to appear at the center of each cube face. (Right) Atoms appear at the corners, as well as at the midpoints and more clearly at the centers of each cube face.