May 18, 2005

Quintillion Clock Takes Lead in Race for Time

PARIS (AFP) -- Japanese scientists say they have made a technical breakthrough in the quest to perfect the world's most accurate clock, a timepiece that would lose only one-quintillionth (a million-million-millionth) of a second per day.

University of Tokyo researcher Hidetoshi Katori and colleagues devised a "pendulum" of strontium atoms that ride on the crest of highly stable laser-generated lightwaves, according to their study, which appears on Thursday in Nature, the weekly British science journal.

So-called optical clocks have a potential for accuracy of one in 10 to the power of 18, or 10 followed by 18 zeroes (one-quintillionth).

The best clocks today use caesium 133 atoms that absorb radio waves and have an accuracy of 10 to the power of 15 -- in other words, they lose a quadrillionth (a tenth of a billionth) of a second per day.

But caesium clocks have reached their limit because radio waves operate at a much lower frequency than optical waves.

The Japanese work is the latest step in an international race to develop a laser-powered atomic clock.

The first big announcement was made in 2001 by the US National Institute of Standards and Technology (NIST), which used a laser and a single mercury ion to provide the "tick."

This was leapfrogged last year by Britain's National Physical Laboratory (NPL), which claimed a big improvement in accuracy by trapping a strontium ion, a technique that is different from Katori's.

These prototype clocks are unlikely to appear on anyone's wrist or mantelpiece any time soon.

Their main outlets are satellite navigation and broadband networks which move information around the Internet, where precision timing is critical.

And they also have potential use for physicists testing the theories of relativity and quantum electrodynamics.