Thorium-229 Study Paves Way for Ultra-Precise Nuclear Clocks

Physicists have now demonstrated all the crucial components that make up a nuclear clock—a device that tells time by measuring tiny energy changes within atomic nuclei. Such a clock could significantly enhance measurement precision and offer new insights into fundamental physics.

Researchers measured the frequency of light that causes the atomic nucleus of the rare isotope thorium-229 to transition to a higher energy state, the "tick-tock" of the nuclear clock, with an accuracy 100,000 times greater than the best previous timing devices. They achieved this by synchronizing energy conversions with the world's most precise clocks. This study, led by the Joint Institute for Laboratory Astrophysics (JILA) in the United States, was recently published in the journal Nature.

This breakthrough stems from the use of a laser device called a "frequency comb" to probe the thorium-229 nucleus. Strictly speaking, this device is not yet a clock as it has not been used for actual timekeeping. However, this impressive result indicates that the development of a nuclear clock is within reach.

Currently, the most precise clocks are atomic clocks, which employ laser timing—where the laser frequency is precisely modulated to match the energy transfer between two internal levels of an atom. The most accurate atomic clocks would only lose a second every 400 billion years. The functioning principle of a nuclear clock is slightly different, timing through energy transfers of protons and neutrons, with its tick-tock coming from transitions between excited states of these particles, not electron transfers.

This energy transfer requires higher frequency ultraviolet light, resulting in a faster tick rate that could potentially surpass the precision of atomic clocks. However, the greatest potential advantage of a nuclear clock lies in its combined precision and stability. Particles within the atomic nucleus are less sensitive to external disturbances like electromagnetic fields compared to electrons, making nuclear clocks potentially more portable and robust.