New Atomic Clock Could Be 1,000 Times Better Than Today's Best

Media Contact: Fred McGehan (Boulder), (303) 497-3246

Researchers at the Commerce Department's National Institute of Standards and Technology have demonstrated a new kind of atomic clock that has the potential to be up to 1,000 times more accurate than today's best clock. They reported the findings July 12, 2001 in Sciencexpress, an online publication of Science Magazine.

The new clock is based on an energy transition in a single trapped mercury ion (a mercury atom that is missing one electron). Building a clock based on such a high-frequency transition was previously impractical because it requires both "capturing" the ion and holding it very still to get accurate readings, and having a mechanism that can "count" the ticks accurately at such a high frequency.

The new optical clock brought together recent advances in three areas of physics: the trapping and cooling of atoms and ions with lasers, frequency-stabilized lasers, and a new optical frequency "comb" that combines a femtosecond laser with non-linear optical fibers to provide a simple, direct, and exact linkage between microwave and optical frequencies. It is the last development that enables the device to count individual cycles of such a high frequency without skipping any, and thus permits the readout of time.

Precise time-keeping underlies much of the structure of modern civilization, including navigation, electric power management, and communications. It also has made possible significant advances in astronomy and physics. Today the best clocks are based on a natural atomic resonance of the cesium atom -- the atomic equivalent of a pendulum. For example, NIST-F1, one of the world's most accurate time standards, neither gains nor loses a second in 20 million years.

How good a clock is depends on stability and accuracy -- whether the clock provides a constant, unchanging output frequency, and how close the measured frequency is to the fundamental atomic resonance that provides the clock's "tick." One advantage of the new clock is that it ticks much faster.

Today's international time and frequency standards, such as NIST-F1, measure an atomic resonance of about 9 billion cycles per second. By contrast, the new NIST device monitors an optical frequency more than 100,000 times higher or about 1 quadrillion cycles per second.