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New Ytterbium Atomic Clocks are the Most Stable Ever

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Aug 22, 2013 05:07 PM EDT
Ytterbium lattice atomic clock
NIST's ultra-stable ytterbium lattice atomic clock. Ytterbium atoms are generated in an oven (large metal cylinder on the left) and sent to a vacuum chamber in the center of the photo to be manipulated and probed by lasers. Laser light is transported to the clock by five fibers (such as the yellow fiber in the lower center of the photo).
(Photo : Burrus/NIST)

A new pair of experimental ytterbium atomic clocks at the National Institute of Standards and Technology (NIST) -- the agency responsible for keeping the official time in the US -- have set a new record for stability.

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Atomic clocks have a reputation for always being on time, accurate down to fractions upon fractions of a second -- intervals so small that their precision becomes insignificant in most peoples' day-to-lives. Yet atomic clocks are essential in many frequently-used technologies including GPS and to control the wave frequency of television broadcasts.

An atomic clock's stability can be thought of as how precisely the duration of each tick matches every other tick, the NIST said in a statement. Typical atomic clocks use atoms of cesium or rubidium to maintain accuracy. The atomic clock used for official time-keeping in the US, NIST F-1, is a cesium-based clock.

The new ytterbium clocks tick with even more stability than the NIST F-1, "stable to within less than two parts in 1 quintillion (1 followed by 18 zeros), roughly 10 times better than the previous best published results for other atomic clocks," the NIST said.

"The stability of the ytterbium lattice clocks opens the door to a number of exciting practical applications of high-performance timekeeping," said NIST physicist Andrew Ludlow.

Like other atomic clocks, the new ytterbium clocks rely upon cooling atoms down to near absolute zero. The atoms, frozen to just 10 millionths of a degree above absolute zero, are suspended in an optical lattice framework. A laser that "ticks" 518 trillion times per second provokes a measurable transition between energy levels in the atoms, of which there are about 10,000. The large number of atoms is key to the clocks' high stability, the NIST said.

To provide the best results, the ticks of any atomic clock must be averaged for some period. The new ytterbium clocks can achieve that average exponentially faster than other atomic clocks.

The NIST-F1 cesium fountain clock, for example, must be averaged for 400,000 seconds (about five days) to achieve its best performance.

The new ytterbium clocks achieve that same result in about one second of averaging time.

A research paper detailing the specifics and performance of the new atomic clocks is published in the journal Science.

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