Nuclear clocks: What is their importance and are they becoming more attainable?

 

Nuclear clocks

Nuclear clocks: What is their importance and are they becoming more attainable?

Nuclear clocks represent the latest advancement in ultra-precise timekeeping. Recent publications in the journal Nature have proposed two new methods and techniques for constructing these clocks.

Timekeeping has become more precise as humans have developed more efficient clocks; however, a standard quartz wristwatch can lose a minute in a week. This remarkable accuracy is essential for the functioning of mobile phone networks and many other aspects of our daily lives.

What are atomic and nuclear clocks?

The most accurate method of measuring time currently in use is what is known as the atomic clock, which takes advantage of the natural oscillations of the atom.
To measure an atom's oscillations, researchers stimulate it with laser energy and can track the oscillations during the laser pulse, using these oscillations as "clicks" to determine the passage of time. The best atomic clocks guarantee that they won't advance or fall behind by a single second over the estimated age of the universe, which is 14 billion years.

For the past two decades, Andrei Derevyanko, a theoretical physicist at the University of Nevada, Reno, has contributed to the development of unprecedented timekeeping accuracy through his research on atomic clocks. Recently, Derevyanko joined two large teams of theoretical and experimental physicists working on nuclear clocks, according to the University of Nevada News website.

He performed calculations that enabled researchers to understand the observed clock signal and helped determine the development paths for nuclear clocks. "Nuclear clocks, when completed, can be incredibly accurate, even more accurate than atomic clocks," Derevyanko said.

Derevyanko explained that nuclear clocks operate similarly to atomic clocks, but they measure the nucleus of the atom instead of the atom itself. This makes them virtually immune to external forces that could affect the accuracy of an atomic clock, thus greatly improving their precision.

He said: "It is much more difficult to examine the nucleus of an atom than to examine the atom itself, and that is why we have atomic clocks and not nuclear clocks."
Examining the nucleus requires lasers that humans have not yet been able to develop, with the exception of a unique and rare isotope, thorium-229, which is a promising candidate for timekeeping. Thorium-229 is produced by the decay of uranium-233, which is used in nuclear reactors. An isotope is a variant of the same chemical element that differs in the number of neutrons in its nucleus.

Derevyanko contributed to the development of a new method for processing thorium-229 and converting it into a thin layer for use in watches, reducing the amount of this rare and radioactive material and thus making it cheaper and safer. He said, "This will open up this new field of scientific research."

The thinness of these layers also leads to the emergence of new quantum effects, which Derivianko is interested in studying in depth. The decay of thorium-229 may provide new methods for studying thorium compounds, potentially contributing to research on nuclear power generation.

Derevyanko's latest work, published in the journal Nature, expands efforts to develop the atomic clock by demonstrating, for the first time, the successful use of laser spectroscopy—a method previously only theoretical. Laser spectroscopy is a scientific technique that uses lasers to study the properties of atoms or molecules.

Physicists have long used Mössbauer spectroscopy to observe the atom's nucleus and its sensitivity to its surrounding environment, information that is crucial for understanding the limits of clock accuracy.

In his latest publication, Derevyanko returns to thorium-229, this time paired with two oxygen atoms, to use Mössbauer laser spectroscopy for the first time. Previously, materials had to be transparent to light to record nuclear transitions, but with Mössbauer laser spectroscopy, opaque materials can be used, allowing for the study of an entirely new class of materials using this technique. This method improves the spectrometer's ability to detect nuclear transitions in a variety of materials.

Development of nuclear clocks

Over the past two decades, Derevyanko has worked on innovating, developing, and improving several categories of clocks. In 2012, he published an article proposing an atomic clock, in collaboration with Alex Kuzmich, currently at the University of Michigan, demonstrating that an atomic clock would greatly improve timekeeping accuracy, and proposing a specific platform capable of achieving this precision.
A research paper published in 2012 provided a major impetus for the search for a rare, narrow spectral line resembling a "needle in a haystack"—a spectral line that could excite the thorium-229 nucleus. This line was finally found within the ultraviolet part of the light spectrum in 2024.

More recently, Derevyanko has been working on the theory of solid-state nuclear clocks in close collaboration with experimental teams at UCLA and the JILA Institute. This work led to the first detection of a nuclear clock signal in 2024 and has developed ideas that could change the course of this field for years to come.

Derivianko said, "If we understand the complex mechanisms, we will not only be able to invent the watch mechanism, but also improve its performance."
The theory has helped to greatly improve the accuracy of watches and reduce their size.
Derevyanko says: "One of the dreams of this community is to have ultra-precise, portable watches. Currently, the best portable watches are the size of a large cabinet. Our research paper suggests the possibility of making an ultra-precise watch the size of a smartphone, which can be carried by hand."

There are many applications for more precise clocks. Nuclear clocks can be used in satellites for global positioning and communications systems, where many atomic clocks are employed, as well as in geodetic measurements of gravity, which varies around the planet.

Geodetic measurements—the science of measuring the shape and size of the Earth and precisely determining the location of points on it—can also identify potential mineral resources based on the unique densities of minerals. Nuclear clocks can also aid in the search for dark matter.