Two Teams Build the First Working Nuclear Clocks Using Thorium-229
Two independent groups reported the first working nuclear clocks in Nature on 7 October 2026, both embedding the radioactive isotope thorium-229 in a calcium fluoride crystal and locking a laser to its nuclear transition frequency. Unlike atomic clocks, which count transitions of electrons between energy levels, a nuclear clock counts a transition inside the nucleus - far smaller and better shielded from stray electromagnetic fields, so potentially far more stable. The teams, led by Thorsten Schumm and Shiqian Ding, already used their clocks to search for dark matter at a sensitivity rivalling the best atomic clocks.
The SI second is defined by the caesium-133 hyperfine transition frequency of 9,192,631,770 Hz | Thorium has atomic number 90 and is a weakly radioactive actinide; India holds among the world's largest monazite-based thorium reserves | Optical atomic clocks commonly use strontium or ytterbium atoms