Clock Tells Time at Such Speed
That Reading It Becomes Challenge

The newest atomic clock is so accurate that its creators theorize that it will neither lose nor gain a second in 4.5 billion years. And, they note that their clock is so promising, it's being tested for use in navigating Global Positioning System satellites and to time minute biological processes, such as protein folding.

But how do you read the time on such a fast clock?

The scientists who designed the new "all-optical-atomic clock" will describe their efforts to count faster and faster things, as the division between "pulses" becomes smaller and smaller.

Using a femtosecond laser to measure time intervals too tiny to be measured in nanoseconds, Scott A. Diddams, a researcher with the National Institute of Standards and Technology in Boulder, Colorado, and his colleagues were able to keep time with greater precision than can be done with existing atomic clocks, by five orders of magnitude. At the American Association for the Advancement of Science (AAAS) Annual Meeting, the researchers will discuss improvements in the femtosecond laser technology, and their efforts to make counters for the new optical clocks.

The optical clock was made possible by technological advances in measuring optical frequencies, and in capturing and cooling single ions to very low temperatures. The clock uses non-linear optical fibers to generate optical-frequency "combs," which are used to determine frequencies by counting the number of "teeth" in the comb.

"We know the clock is very stable, so now our research is focused on seeing exactly how accurate it is," Diddams said.

Diddams and his colleagues developed the optical clock based on a single trapped mercury ion, and they promise that their research may someday end the reign of the microwave atomic clocks, which use cesium 133 atoms to determine the time. Cesium atoms resonate exactly 9,192,631,770 times per second, when irradiated by a magnetic microwave field. So clocks that adhere to that frequency are extremely accurate. The cesium clock is thought to be able to maintain the correct time for 20 million years—a mere blink of an eye, however, when compared to the 4.5 billion years of accuracy claimed for the optical timekeeper.

14 February 2003