Physicists develop world's most accurate atomic clock

Washington, Feb 15 : Physicists have developed a new atomic clock that surpasses previous records for accuracy of current U.S. time standard, making it the world's most accurate atomic clock.

Developed by physicists at JILA, a joint institute of the Commerce Department's National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder, the new clock is based on thousands of strontium atoms trapped in grids of laser light.

In the JILA clock, a few thousand atoms of the alkaline-earth metal strontium are held in a column of about 100 pancake-shaped traps called an "optical lattice." The lattice is formed by standing waves of intense near-infrared laser light.

Forming a sort of artificial crystal of light, the lattice constrains atom motion and reduces systematic errors that occur in clocks that use moving balls of atoms.

Using thousands of atoms at once also produces stronger signals and eventually may yield more precise results than clocks relying on a single ion, such as mercury.

This experimental strontium clock is in fact now the world's most accurate atomic clock based on neutral atoms, more than twice as accurate as the NIST-F1 standard cesium clock located at the NIST campus in Boulder.

This new clock would neither gain nor lose a second in more than 200 million years, compared to NIST F-1's current accuracy of over 80 million years.

For the evaluation of the JILA strontium clock, researchers remotely compared it to a third NIST atomic clock, an experimental model based on neutral calcium atoms.

The best clocks can be precisely evaluated by comparing them to other nearby clocks with similar performance; very long-distance signal transfer, such as by satellite, is too unstable for practical, reliable comparisons of the new generation of clocks.

In the latest experiment, signals from the two clocks were compared via a 3.5-kilometer underground fiber-optic cable.

"This is our first comparison to another optical atomic clock," said NIST/JILA Fellow Jun Ye, who leads the strontium project.

The strontium and calcium clocks rely on the use of optical light, which has higher frequencies than the microwaves used in NIST-F1. Because the frequencies are higher, the clocks divide time into smaller units, offering record precision. ecause Ye's group is able to measure and control interactions among so many atoms with such exquisite precision, the JILA work is expected to lead to new scientific tools for quantum simulations that will help scientists better understand how matter and light behave under the strange rules governing the nanoworld.

ANI