From: Reuters
Published February 15, 2008 03:59 PM

Precision clock traps atoms in light to keep time

By Julie Steenhuysen

CHICAGO (Reuters) - U.S. physicists have made a clock so accurate it will neither gain nor lose even a second in more than 200 million years, a finding sure to please even the most punctually minded.

The clock, described in the Friday issue of the journal Science, outperforms the official atomic clock used by the U.S. Commerce Department's National Institute of Standards and Technology, which promises to keep accurate time down to the second for 80 million years.

The new atomic clock is vying for the title of world's most accurate with another experimental clock developed in the same lab at the Joint Institute for Laboratory Astrophysics, a collaboration between NIST and the University of Colorado in Boulder.

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"These clocks are improving so rapidly that it is impossible to tell which one will be the best," said Tom 0'Brian, head of the Time and Frequency Division at NIST.

Such highly precise clocks are critical for deep space navigation, where even a slight error can make or break a space mission.

The secret to making an extremely accurate clock is speeding up how fast it ticks. "If you make a mistake, you can know about that mistake very fast," said Jun Ye, who developed the atomic clock at JILA.

Ye's clock has 430 trillion "ticks" per second.

Its pendulum uses thousands of strontium atoms suspended in grids of laser light. This allows the researchers to trap the atoms and measure the movement of energy inside.

"Essentially, we are probing the energy structure of the atom. We are probing how electrons make transitions between a set of energy levels," Ye said in a telephone interview.

"This is the time scale that was made by the universe. It is very stable."

To test his clock's accuracy, Ye and colleagues compared it with another optical atomic clock -- this one measuring calcium atoms. This calcium clock is highly stable only over short periods of time, so the researchers had to make fast measurements for their comparisons.

Next Ye wants to take on a clock that measures a single ion, or charged particle, of mercury. This clock, also developed at JILA, was accurate to about 1 second in 400 million years in 2006. Because Ye's clock measures thousands of atoms at once, it produces stronger signals, something Ye thinks may give him an edge.

"These clocks are among the best in the world," John Lowe, leader of the atomic standards group at NIST, said in a telephone interview. "Longer-term experiments will prove which of these clocks may end up becoming the next standard of international agreement."

Ye said pushing for ever more accurate clocks will allow physicists to test some of the basic questions about the nature of the universe.

It also can be used to synchronize telecommunications networks and might some day lead to things like hands-free driving in satellite-guided cars.

"If we can navigate a vehicle on Mars and ask it to settle down on a particular runway, I'm sure we can navigate all the cars on Earth with satellites," Ye said.

(Editing by Maggie Fox and Jackie Frank)

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