World's most accurate timepiece

Physicists have built the world's most accurate timepiece, based on an advanced version of an experimental atomic clock relying on a single aluminum atom.

It is more than twice as precise as the previous pacesetter based on a mercury atom. The new aluminum clock would neither gain nor lose one second in about 3.7 billion years, according to measurements.

The new clock is the second version of National Institute of Standards and Technology (NIST) "quantum logic clock," because it borrows the logical processing used for atoms storing data in experimental quantum computing.

"This paper is a milestone for atomic clocks" for a number of reasons, says NIST postdoctoral researcher James Chou, who developed most of the improvements.

In addition to demonstrating that aluminum is now a better timekeeper than mercury, the latest results confirm that optical clocks are widening their lead - in some respects - over the NIST-F1 cesium fountain clock, the US civilian time standard, which currently keeps time to within one second in about 100 million years.

Because the international definition of the second (in the International System of Units, or SI) is based on the cesium atom, cesium remains the "ruler" for official timekeeping, and no clock can be more accurate than cesium-based standards such as NIST-F1.

The logic clock is based on a single aluminum ion (electrically charged atom) trapped by electric fields and vibrating at ultraviolet light frequencies, which are 100,000 times higher than microwave frequencies used in NIST-F1 and other similar time standards around the world, says a NIST release.

Optical clocks thus divide time into smaller units, and could someday lead to time standards more than 100 times as accurate as today's microwave standards. Higher frequency is one of a variety of factors that enables improved precision and accuracy.

These findings are slated for publication in Physical Review Letters.