New Experimental Atomic Clock Surpasses Accuracy Of Current U.S. Standard Time Clock (2/15/2008)

JILA Fellow Jun Ye with new atomic clock. Photo courtesy JILA

A next-generation atomic clock developed by researchers from the National Institute of Standards and Technology and the University of Colorado at Boulder has been shown to be accurate to within one second over 200 million years, surpassing the accuracy of the current U.S. time standard atomic clock more than two-fold.

The new atomic clock, which is based on the resonance of thousands of strontium atoms trapped in grids of laser light, surpasses the accuracy of the NIST F-1 cesium clock used as the U.S. time standard, according to a team of researchers at JILA, a joint institute of NIST and CU-Boulder. The experimental strontium clock is now the world's most accurate atomic clock that uses neutral atoms, as opposed to charged atoms. The NIST-F1 cesium clock is accurate to within a second over 80 million years.

Atomic clocks keep time by counting the high-speed electronic "ticks" generated by oscillations of atoms as they jump back and forth between different energy states. The resonance of the atoms serves the same purpose as a pendulum on a clock, although the ticks in the new JILA strontium clock occur at about 430 trillion times per second.

The JILA strontium clock was evaluated remotely by comparing it to a third NIST atomic clock, an experimental model based on neutral calcium atoms. In the latest experiment, signals from the two clocks were compared using a two-mile underground fiber-optic cable.

A paper on the subject by scientists from JILA and NIST appears in the Feb. 14 online edition of Science.

"This is our first comparison to another optical atomic clock," says NIST/JILA Fellow Jun Ye, who leads the strontium project. "As of now, Boulder is in a very unique position. We have all the ingredients, including multiple optical clocks and the fiber-optic link, working so well. Without a single one of these components, these measurements would not be possible. It's all coming together at this moment in time."

The development and testing of a new generation of optical atomic clocks is important because highly precise clocks are used to synchronize telecommunication networks and deep-space communications, as well as for navigation and positioning, said Ye, who is an adjoint professor in CU-Boulder's physics department. The race to build even better clocks is expected to lead to new types of gravity sensors, as well as new tests of fundamental physical laws to increase understanding of the universe.

The strontium and calcium clocks rely on the use of optical light, which has higher frequencies than the microwaves used in the NIST-F1 clock. Because the frequencies are higher, the clocks divide time into smaller units, Ye said. The work reported in Science is the first optical atomic clock comparison over that long a distance, an important step for worldwide development of future standards.

NIST and JILA are home to optical clocks based on a variety of atoms, including strontium, calcium, mercury, aluminum and ytterbium, each offering different advantages. Ye and his team plan to compare the strontium clock to the world's most accurate clock, NIST's experimental mercury ion clock. The mercury ion clock was accurate to about 1 second in 400 million years in 2006, and has improved since then.

The JILA research is supported by the Office of Naval Research, NIST, the National Science Foundation and the Defense Advanced Research Projects Agency.

In addition to Ye, co-authors on the Science paper included JILA's Andrew Ludlow, Tanya Zelevinsky, Gretchen Campbell, Sebastian Blatt, Martin Boyd, Marcio de Miranda, Michael Martin, Jan Thomsen and Seth Foreman. NIST co-authors included Tara Fortier, Jason Stalnaker, Scott Diddams. Yann Le Coq, Zeb Barber, Nicola Poli, Nathan Lemke, Kristin Beck and Chris Oates.

Note: This story has been adapted from a news release issued by the University of Colorado at Boulder

Post Comments: