New atomic clock could be 1000 times better than today's best

July 13, 2001

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

Researchers at the National Institute of Standards and Technology have demonstrated a new kind of atomic clock that has the potential to be up to 1000 times more accurate than today's best clock. They report the findings in a recent issue of Science Express, an online publication of Science.

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.

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.

In principal, a frequency standard or clock based on the new mechanism could be proportionately more accurate and stable than the current standard. Indeed, the new device already has demonstrated a short-term stability significantly better than any existing atomic clock. Researchers will continue work to determine its accuracy.