Extreme measures: Atom interferometry's precision could make it the Swiss Army knife of physics

Science News,  Feb 16, 2008  by Ewen Callaway

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Such precision has become routine in lab experiments, but building an interferometer that can take the bumps of an airplane or helicopter ride demands changes to lab models, Lowell says. "We have systems that are now smaller and more compact and work with the flip of a switch, instead of a system that takes up massive chunks of tabletops and a rack of equipment, and takes armies of grad students to keep operating" he says.

A CONSTANT STRUGGLE On a sprawling 20-by-20-foot table at the National Institute of Standards and Technology (NIST) in Gaithersburg, Md., physicist Kris Helmerson shows off an instrument that does in fact demand an army of graduate students.

On one end of the gigantic table, the eerie glow of an orange laser dances around a dozen little lenses and mirrors set at different angles and orientations. The laser will chill sodium atoms to a hair above absolute zero. In this state, hundreds of thousands of atoms together act like one big wave, called a Bose-Einstein condensate.

Just creating the condensate earned Nobel prizes in 2001 for the three physicists who accomplished the feat in 1995. Helmerson, who works in NIST'S Advanced Measurement Laboratory, uses atom interferometry to measure more esoteric properties of Bose-Einstein condensates. In 2000, for instance, he and colleague Bill Phillips put a kind of sound wave, called a soliton, into their condensate. And in 2006, the team created a whirlpool-like vortex out of a condensate.

Less exotic pursuits keep other atom interferometers busy. The most common experiments are measurements of physical constants, the numbers describing gravity, electricity, and other forces that make the universe tick. Over the past two centuries, light interferometry refined these figures, and atom measurements will do the same, says physicist Steven Chu, director of the Lawrence Berkeley National Laboratory in California.

Chu, whose lab is based at Stanford, has shown that atom interferometry can achieve the same precision as conventional methods in measuring the acceleration due to gravity on Earth. With technological improvements, atom interferometry could do even better.

Atom interferometry could also refine another measure of gravity--the constant that describes the gravitational tug between any two objects, which physicists call "big G." Currently, G'S value is known only to one part in 10,000. That's equivalent to knowing the length of 100 meters (roughly a football field) down to a centimeter--not very precise by the usual standards for fundamental constants of nature. "It's kind of embarrassing," Cronin says.

In a paper in the Feb. 8 Physical Review Letters, a team of Italian physicists suggests that atom interferometry could improve the precision of G by at least a factor of l0. In another paper, the same team used atom interferometry to measure gravity between objects separated by a few millionths of a meter. Such measurements could reveal a breakdown in Newton's laws of gravity, which could have implications for theories suggesting the existence of extra dimensions of space.