New NIST Atomic Clock Achieves Landmark Precision, Poised for Global Role in Timekeeping

A newly developed atomic clock, NIST-F4, has been confirmed as one of the most accurate timekeepers in the world, positioning it to become a designated primary frequency standard—a key component in maintaining global time synchronization. Developed by the National Institute of Standards and Technology (NIST), the clock enhances the stability of official U.S. time and strengthens the international timekeeping network.

The cesium-based NIST-F4 clock, which operates on a “fountain” design, measures time by detecting a specific, constant frequency produced by cesium atoms. This method, internationally recognized since 1967, defines the duration of one second. In tests recently published, NIST-F4 demonstrated such precision that it would be off by less than a second even after 100 million years. Its performance matches a select group of similar devices used by only ten countries worldwide.

NIST-F4 contributes directly to UTC(NIST), the U.S. version of Coordinated Universal Time, by calibrating it with extreme accuracy. This makes it essential for applications requiring exact time, including data center operations, financial transactions, and global communications. The clock supports the hydrogen maser clocks that keep national time signals, which are broadcast via radio and internet systems and used billions of times each day.

Fountain clocks like NIST-F4 are extremely rare, with fewer than 20 in operation globally, and are typically constructed and maintained by national measurement institutes. The process of building NIST-F4 began after researchers determined that the original fountain clock, NIST-F1, required significant refurbishment. A complete rebuild of the core measurement component, the microwave cavity, was carried out to achieve the necessary tolerances for precision. The team then conducted extensive evaluations to rule out influences from environmental variables and ensure measurement stability.

Following the rebuild, NIST-F4’s performance was documented in the journal Metrologia, showing a frequency accuracy within 2.2 parts in 10^16. This level of precision qualifies the clock for submission to the International Bureau of Weights and Measures (BIPM), which oversees the certification of global time standards. The BIPM is currently reviewing NIST-F4 for formal recognition.

NIST-F4 now runs alongside NIST-F3 and is operational around 90% of the time, with at least one fountain clock active at all times to support the U.S. time scale. These clocks periodically submit data to BIPM for inclusion in the calculation of Coordinated Universal Time. The success of NIST-F4 has reinforced NIST’s role in global timekeeping and renewed its leadership in developing high-precision frequency standards.

Article by multiple RFHC contributors, based upon information from the National Institute of Standards and Technology (NIST) press release.

Video Spotlight