Optical atomic clocks use electronic energy levels to keep track of time precisely. They measure time by tuning laser light to frequencies that cause electrons to jump between energy levels.
An international research team led by scientists at JILA, a joint institute of the National Institute of Standards and Technology (NIST) and the University of Colorado Boulder, has unveiled the world’s first nuclear clock prototype. Scientists have demonstrated critical elements of a nuclear clock.
Using a specially designed ultraviolet laser, scientists accurately measured the frequency of an energy jump in thorium nuclei embedded in a solid crystal. They also harnessed an optical frequency comb as a highly accurate light ruler to count ultraviolet wave cycles that generate energy jump.
World’s first optical atomic clock with highly charged ions
What is the nuclear clock?
A nuclear clock is a timekeeping device that uses signals from the nucleus of an atom. These devices are expected to be more accurate than existing atomic clocks. This development will prompt more precise navigation systems (with or without GPS), faster internet speeds, more reliable network connections, and more secure digital communications.
Also, it will improve tests of fundamental theories describing the workings of the universe, detect dark matter, and verify whether the constants of nature are truly constant, allowing for verification of theories in particle physics without the need for large-scale particle accelerator facilities.
How nuclear clock will work?
As mentioned, a nuclear clock uses energy jumps generated by ultraviolet wave cycles within an atom’s nucleus. These energy jumps act like flipping a light switch. Shining laser light with the exact amount of energy needed for this jump can flip this nuclear “switch.”
However, the laser light for this should be high-frequency, meaning more wave cycles per second. This higher frequency is directly related to a greater number of “ticks” per second, leading to more precise timekeeping.
Superposition can impact timekeeping in high-precision clocks
Making a nuclear clock is very hard
Making energy jumps requires atomic nuclei to be hit by high-energy coherent X-rays. Thus, scientists considered thorium-229, an atom whose nucleus has a smaller energy jump than any other known atom, requiring ultraviolet light (which is lower in energy than X-rays).
In this study, scientists reported that they have created all the essential parts of a clock: the thorium-229 nuclear transition to provide the clock’s “ticks,” a laser to create precise energy jumps between the individual quantum states of the nucleus, and a frequency comb for direct measurements of these “ticks.”
They achieved a level of precision that is one million times higher than the previous wavelength-based measurement. When they compared the ultraviolet frequency directly to the optical frequency used in one of the world’s most accurate atomic clocks, they found that they had established the first direct frequency link between a nuclear transition and an atomic clock.
This direct frequency link and increase in precision are a crucial step in developing the nuclear clock and integrating it with existing timekeeping systems.
“The research has already yielded unprecedented results, including the ability to observe details in the thorium nucleus’s shape that no one had ever observed before,” noted scientists.
Journal Reference:
- Zhang, C., Ooi, T., Higgins, J.S. et al. Frequency ratio of the 229mTh nuclear isomeric transition and the 87Sr atomic clock. Nature 633, 63–70 (2024). DOI: 10.1038/s41586-024-07839-6