Major step forward for nuclear clock paves the way for ultra-precise timekeeping

The world moves to the rhythm of atomic clocks, but a new type of clock under development – ​​a nuclear clock – could revolutionize the way we measure time and study fundamental physics.

An international research team led by scientists from JILA, a joint institute of the National Institute of Standards and Technology (NIST) and the University of Colorado Boulder, has demonstrated the key elements of a nuclear clock. A nuclear clock is a new type of time-measuring device that uses signals from the nucleus of an atom.

The team presents the results in the September 4 issue of the journal Nature as a cover story.

The team used a specially designed ultraviolet laser to precisely measure the frequency of an energy jump in thorium nuclei embedded in a solid crystal. They also used an optical frequency comb, which acts like an extremely precise light ruler, to count the number of cycles of ultraviolet waves that create this energy jump. While this lab demonstration is not a fully developed nuclear clock, it contains all the basic technology to create one.

Nuclear clocks could be much more accurate than current atomic clocks, which provide official international time and play a major role in technologies such as GPS, internet synchronization and financial transactions.

For the general public, this development could eventually mean even more accurate navigation systems (with or without GPS), faster Internet speeds, more reliable network connections and more secure digital communications.

Beyond everyday technologies, nuclear clocks could improve tests of fundamental theories about how the universe works, potentially leading to new discoveries in physics. They could help detect dark matter or test whether the constants of nature are truly constant, allowing theories of particle physics to be tested without the need for large-scale particle accelerators.

Laser precision in timing

Atomic clocks measure time by tuning laser light to frequencies that cause electrons to jump between energy levels. Nuclear clocks would use the energy jumps in the tiny central region of an atom, known as the nucleus, where particles called protons and neutrons pack together.

These energy jumps are a bit like flipping a switch. By shining a laser light with the exact amount of energy needed for that jump, you can flip that nuclear “switch.”

A nuclear clock would have major advantages in terms of accuracy. Compared to electrons in atomic clocks, the nucleus is much less affected by external disturbances such as stray electromagnetic fields. The laser light needed to cause energy jumps in nuclei is much higher in frequency than that required for atomic clocks.

This higher frequency, which means more wave cycles per second, is directly related to a greater number of “ticks” per second and therefore leads to more accurate timekeeping.

But creating a nuclear clock is very difficult. To achieve energy jumps, most atomic nuclei must be hit with coherent X-rays (a form of high-frequency light) that have much higher energy than current technology can produce. So scientists focused on thorium-229, an atom whose nucleus has a smaller energy jump than any other known atom, requiring ultraviolet light (which has less energy than X-rays).

In 1976, scientists discovered this energy jump in thorium, known as a “nuclear transition” in physics parlance. In 2003, scientists proposed using the transition to create a clock, and they didn’t observe it directly until 2016. Earlier this year, two different research teams used ultraviolet lasers they had created in the lab to flip the nuclear “switch” and measure the wavelength of light needed to do the trick.

In this new work, the JILA researchers and their colleagues create all the essential elements of a clock: the nuclear transition of thorium-229 to provide the clock’s “ticks,” a laser to create precise energy jumps between different quantum states of the nucleus, and a frequency comb for direct measurements of these “ticks.”

This measurement achieved a level of precision one million times higher than that of the previous measurement based on wavelength. In addition, the researchers directly compared this ultraviolet frequency to the optical frequency used in one of the most accurate atomic clocks in the world, which uses strontium atoms, thus establishing the first direct frequency link between a nuclear transition and an atomic clock.

This direct frequency link and increased accuracy represent a crucial step in the development of the nuclear clock and its integration into existing timekeeping systems.

The research has already yielded unprecedented results, including the ability to observe details in the shape of the thorium nucleus that no one has ever observed before – it’s like seeing individual blades of grass from an airplane.

Towards a nuclear future

While this is not yet a working nuclear clock, it is a crucial step toward creating such a clock that could be both portable and extremely stable. The use of thorium embedded in a solid crystal, combined with the reduced sensitivity of the core to external disturbances, opens the way to potentially compact and robust timing devices.

“Imagine a wristwatch that wouldn’t lose a second even if you let it run for billions of years,” said Jun Ye, a physicist at NIST and JILA. “While we’re not quite there yet, this research brings us closer to that level of precision.”

The research team included researchers from JILA, a joint institute of NIST and the University of Colorado Boulder, the Vienna Center for Quantum Science and Technology, and IMRA America, Inc.

This article is republished with kind permission from NIST. Read the original article here.