Imperturbable Ytterbium Reverberates Superbly, Scientists Say

Article excerpt

Using lasers and a rare metal element called ytterbium, scientists at the US National Institute of Standards and Technology (NIST) say they have crafted a pair of the world's most stable timepieces.

According to research published in the current issue of the journal Science, the new clocks are stable to within one part in a quintillion (that's a one with 18 zeros after it). By comparison, your bog-standard quartz clock is stable to roughly six parts in a million, drifting off by about a second every two days. The new clock is roughly 10 times more stable than its predecessors, NIST says.

The stability of these clocks "opens the door to a number of exciting practical applications of high-performance timekeeping," says NIST physicist and co-author Andrew Ludlow, in a press release.

Atomic clocks, which are used to calibrate sensitive electronics such as those used by global positioning systems and to conduct sensitive experiments in fields as diverse as geology, particle physics, and radio astronomy, rely on the vibrations of atoms. Each element has its own natural vibration rate, and if you know what that rate is, you can use it to keep time.

For instance, the NIST-F1 cesium fountain clock, which establishes the official US time, works by zapping atoms of a stable isotope of the element cesium called cesium 133 with microwave beams and then measuring the rate at which these excited atoms emit photons. An international agreement in 1967 defined one second as exactly 9,192,631,770 vibrations of a cesium 133 atom. …


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