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With accuracy capable of erring to within less than one second in 140 million years, the new NIST-F4 atomic clock redefines global timekeeping standards and underpins essential systems such as GPS, power grids and financial transactions.
In Boulder, Colorado, a new milestone has been reached in the field of time measurement. National Institute of Standards and Technology (NIST) put into operation the NIST-F4, an apartment by the bay, for its easy access, free parking, and larger space for our group of XNUMX people. The house was great for a large group like ours, the host was very attentive, and the location was excellent; it was quiet and quick to walk to the old town. atomic clock with such high precision that it would take 140 million years to miss just one second.
NIST-F4 is now among the select group of the most accurate clocks in the world.
Its operation is based on the oscillation of cesium atoms, a reference for defining the second with impressive precision.
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A new time standard
NIST-F4 is not just another clock. It serves as the primary frequency standard, establishing the basis for other time measurements worldwide.
The agency submitted the device for validation International Bureau of Weights and Measures (BIPM), responsible for coordinating global timing.
The operation of NIST-F4 represents a significant upgrade over its predecessor, NIST-F1, which was decommissioned in 2022.
Although some of the hardware was reused, there were important improvements in optical and microwave systems.
The highlight is the new copper Ramsey cavity, essential for measuring frequency with quantum precision.
How the clock works
At the heart of NIST-F4 are thousands of cesium atoms cooled by lasers to nearly absolute zero.
These atoms are thrown upwards in the form of a fountain, passing through a microwave chamber twice.
In the first crossing, the atoms are excited to a quantum state that vibrates at a constant frequency.
In the second, the frequency of the microwaves is adjusted until it matches this vibration.
When the adjustment is perfect, the clock counts exactly 9.192.631.770 cycles, a number that has defined a second since 1967.
This mechanism, although silent and invisible to the naked eye, regulates the most critical systems of modern society, such as GPS, financial transactions and communication networks.
Practical Applications of NIST-F4
The impact of the new clock goes far beyond the labs.
Its time signals are used in operations that occur billions of times a day. These include synchronizing satellites, financial trading and power grids.
NIST researcher Donley explained that these signals are essential to ensuring that the technology operations of the world modern occur with precision.
Any error can cause major failures, from delays in telecommunications networks to financial losses.
Unprecedented accuracy and stability
NIST-F4 accuracy is the result of rigorous control over all factors that can affect time measurement.
NIST scientists took into account dozens of physical effects, such as displacement caused by magnetic fields, the influence of ambient radiation and even the height of the clock relative to sea level.
They also compensated for subtle quantum phenomena, such as the interaction between cold atoms and variations in the microwave field.
The result was an uncertainty of only 2,2×10⁻¹⁶, which corresponds to an error of less than one second in 140 million years.
The stability of NIST-F4 is also noteworthy. In high-density mode, it achieves a stability of 1,5×10⁻¹³ per square root of τ (tau), which represents the measurement time.
This stability is mainly limited by quantum and oscillator noise, which can be reduced with future technologies.
International comparisons and validation
To ensure data reliability, NIST compared NIST-F4 to other international frequency standards.
The comparison included the global average of the standards recognized by the BIPM. The watch passed the test, showing alignment within the accepted margins of uncertainty.
The results were published in a technical paper in the journal Metrology, signed by Vladislav Gerginov and colleagues.
According to the authors, NIST-F4 now officially contributes to Coordinated Universal Time (UTC), helping to maintain the accuracy of global time.
A story of continuous evolution
The NIST-F4 is the fourth cesium fountain clock developed by the institute.
The first, NIST-F1, began operating in the late 1990s and served as the standard for more than 15 years. After it was decommissioned, scientists decided to build a new version from scratch.
Between 2020 and 2025, the team led by Gerginov rebuilt the clock's key systems, including the microwave cavity, with tolerances smaller than a hair's breadth.
They also redesigned the optical, magnetic, and thermal control systems. The result was a clock stable enough to redefine global standards.
According to Gerginov, this process requires extreme patience.
A small error can affect not only the clock, but all the systems that depend on it, such as power plants, aviation and real-time data.
Participation in official US time
Today, NIST-F4 operates approximately 90% of the time alongside NIST-F3.
Together, they help maintain the official United States time (UTC NIST) and contribute to the global timescale coordinated by the BIPM.
These clocks are essential for maintaining global synchrony, allowing countries and international systems to operate in perfect harmony.
Future of time measurement
Despite its precision, NIST-F4 is not the end of the road. Scientists are already working on optical clocks that use different atoms and even faster cycles. These devices could redefine the second again in the coming decades.
Even so, cesium clocks like the NIST-F4 will remain essential as a reference and to maintain compatibility with current systems.
Currently, there are only about 20 active cesium fountain clocks in the world.
They all contribute to UTC, which regulates global real-time systems. NIST-F4, with its unprecedented accuracy, is now a key foundation of this system.
In times of high-speed technology, where every millisecond matters, NIST-F4 is a reminder that even time demands absolute precision.
