spaceSpace and Physics

Atomic Clocks Have Reached A Never-Before-Achieved Level Of Accuracy


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockMar 24 2021, 16:00 UTC
time concept

The three clock measurements were so accurate that their uncertainties never exceeded 0.000000000000000008. Image Credit: CKA/

Researchers from the Boulder Atomic Clock Optical Network (BACON) Collaboration have achieved some incredible breakthroughs in timekeeping. The team was able to compare three atomic clocks with record accuracy over both optical fibers and air, paving the way to the eventual redefinition of the fundamental unit of time: the second.

The work, published in Nature, might not only change how we measure time, as it also reports the three most accurate measurements of natural constants ever made. And it all boils down to measuring frequencies, which humanity truly excels at.


The second is defined by a very specific frequency related to the cesium atom. This specific frequency is the underpinning physical phenomenon of the classic microwave-based atomic clocks. But the new generation of atomic clocks, based on different atoms, is 100 times more accurate than what can be achieved with cesium.

Three Optical Atomic Clocks were used in the experiment. The team compared the aluminum-ion clock and ytterbium lattice clock, located in different laboratories at the National Institute Of Standards And Technology (NIST), with the strontium lattice clock located 1.5 kilometers (just under a mile) away at JILA, a joint institute of NIST and the University of Colorado Boulder. The three clock measurements were so accurate that their uncertainties never exceeded 8 parts in 1018 (or 0.000000000000000008).

"These comparisons are really defining the state of the art for both fiber-based and free-space measurements--they are all close to 10 times more accurate than any clock comparisons using different atoms performed so far," NIST physicist David Hume said in a statement.

Schematic of the links between three optical atomic clocks used in the study. Hanacek/NIST

The team measured the relationship between the natural frequencies of the three atoms measured in pairs (ytterbium-strontium, ytterbium-aluminum, aluminum-strontium). These are the most accurate frequency measurements yet – the precision is outstanding and really opens up a whole new world of scientific explorations.

The focus is obviously first and foremost on the redefinition of the second. Not only are the optical atomic clocks are more precise, but they are also incredibly stable. They wouldn’t lose or gain a single second in a billion years. While these achievements are incredible, there are still steps necessary before the redefinition of the second can happen.

The optical atomic clocks are also so incredibly precise that they can be used by themselves to study the effect of gravity and even study physics beyond current theories, including trying to discover what dark matter is made of.


The work shows that it might be possible to synchronize the best atomic clocks across remote sites on Earth, even sending signals to spacecraft. A new type of atomic clocks might soon be the gold standard for time measurements.

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