Precision clock traps atoms in light to keep time

"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)