Motion System Design

Quantum logic clock is world's best timekeeper

Move over, mercury. Physicists at the National Institute of Standards and Technology (NIST) have built an enhanced version of an experimental atomic clock based on a single aluminum atom. The new timepiece — more than twice as precise as the previous pacesetter based on a mercury atom — would neither gain nor lose a second in about 3.7 billion years, according to scientists.

This clock is the second version of NIST's “quantum logic clock,” so named because it borrows the logical processing used for atoms storing data in experimental quantum computing. In addition, this clock operates optically — using ultraviolet-scale vibrations — to widen the lead over NIST-F1 cesium fountain clocks (the U.S. civilian time standard), and the cesium-based SI definition of a second, both only accurate to within 1 second in about 100 million years.

In contrast, NIST's logic clock is based on a single aluminum ion trapped by electric fields and vibrating at UV light frequencies, which are 100,000 times higher than microwave frequencies used in NIST-F1 and similar time standards around the world. Because it divides time into smaller units, it could lead to standards more than 100 times as accurate as today's microwave-scale standards.

Besides aluminum, NIST scientists are working on experimental optical clocks based on other atoms. A second version of the logic clock would prove that laboratories could replicate the clock should it spawn a new standard.

Why care? The extreme precision offered by optical clocks is already providing record measurements of possible changes in the fundamental constants of nature, which has important implications for testing the laws of physics, such as Einstein's theories of relativity. Next-generation clocks might also lead to new types of gravity sensors for exploring underground natural resources and fundamental studies of Earth. Other applications may include ultra-precise autonomous navigation, such as landing planes by GPS. This work was supported in part by the Office of Naval Research. For more information, visit

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