Clocks in the News

U.S. Scientists Create World's Most Precise Clock

July 2, 2001 - Reuters

Using sophisticated laser technology and a lone atom of mercury, U.S. government scientists have created the world's most precise clock -- a device that ticktocks circles around the best previous timepieces, according to research published on Thursday.

Scientists at the National Institute of Standards and Technology (NIST) in Boulder, Colorado, developed a new type of atomic clock that produces about 1 quadrillion ``ticks'' per second and promises to be far more accurate than the current top standard in time measurement -- cesium-based microwave atomic clocks.

``We've demonstrated for the first time the next generation of atomic clocks, which have the potential to be 100 to 1,000 times more accurate than the current cesium-based microwave clocks,'' physicist Scott Diddams, who led the research appearing in the journal Science, said in an interview.

The new all-optical atomic clock -- so named because of its reliance on laser technology -- measures the shortest intervals of time ever recorded. In fact, those intervals are 100,000 times shorter than those observed by the best current clocks.

The new atomic clock could improve navigation technology, as well as communications technology such as cellular telephones and fiber optics, Diddams said.

The new clock also may help provide answers to some exotic scientific questions relating to Albert Einstein's theory of general relativity and the plasticity of time, Diddams added.

``Some of those (issues) are related to the very idea that maybe time is not constant as our universe evolves,'' he said.

All clocks since the sundial have consisted of two major components: a device that produces a regular tick, such as a pendulum; and some means to count, accumulate and display the passage of time, such as gears driving a pair of clock hands.

Atomic clocks, first developed about 50 years ago, add a third component -- an atom that responds to light or electromagnetic radiation at very specific frequencies in order to control the ``pendulum.''


In the best current atomic clocks, the shining of microwave radiation at a million atoms of the liquid metal cesium controls the tick. These clocks tick about 10 billion times per second. A clock with more ticks can be much more precise.

But the high-speed electronics technology used in the cesium clocks was not equipped to count many more ticks.

``We needed a new clockwork,'' Diddams said.

The new atomic clock does not use cesium atoms, but rather a single cooled ion of the liquid metal mercury (a mercury atom with one electron stripped off) linked to a laser oscillator functioning as a pendulum. The frequency of the mercury ion is 100,000 times higher than the frequency on the cesium atoms.

But by employing another laser to add, in effect, another wheel to the gears, Diddams and his colleagues conjured up a way to keep track of all the ticking.

Ultra-precise clocks have proven very useful. Satellites in the global-positioning system used for navigation are equipped with atomic clocks. The clocks are used in communications systems for synchronizing networks. In fact, the electrical grid for the United States is timed with atomic clocks.

Diddams said advances in timekeeping technology tend to spur leaps forward in a lot of other fields. ``As clocks get better and better, the applications that people dream up just keep getting better and better,'' Diddams said.

He said he envisioned future uses for the new clock in regulating precise orbits for satellites, deep-space navigation and linking together spacecraft. ``You need very precise navigational tools for this,'' Diddams added.

Diddams said the clock exists as components in two of his agencies laboratories in Boulder. ``It's not neatly packaged up in a box that says 'NIST All-Optical Clock.' An outsider would have no idea that it was a clock. We don't have a display on it that says 11 p.m. or whatever.''