Tsinghua Demonstrates 229Th Nuclear Clock at 5x10^-13 Instability, Matching Crystals to 10^-13
Updated
Updated · Nature.com · Oct 7
Tsinghua Demonstrates 229Th Nuclear Clock at 5x10^-13 Instability, Matching Crystals to 10^-13
3 articles · Updated · Nature.com · Oct 7
Summary
Tsinghua researchers locked a 148.4-nm vacuum-ultraviolet laser to a thorium-229 transition in CaF2 crystals, producing an operating nuclear clock with fractional frequency instability of 5x10^-13/√τ.
A 10-μW continuous-wave VUV source, phototube-based absorption readout and feedback to the laser frequency let the system approach the photon-shot-noise limit and average down to the 10^-15 level.
The best performance came from a bubble-free TS1 crystal grown from just 1.4 μg of 229Th; higher transmission and roughly threefold stronger absorption lifted signal-to-noise about 20-fold versus the initial setup.
Clock-transition frequencies in two independently fabricated crystals differed by 5.6x10^2 Hz—2.8x10^-13 fractionally—and both were consistent with earlier JILA measurements, supporting reproducible solid-state nuclear references.
The result, published alongside a near-simultaneous TU Wien report, moves 229Th clocks from spectroscopy to operational devices for compact timekeeping and precision tests of fundamental physics.
What hidden secrets about dark matter might these revolutionary solid-state nuclear clocks finally unlock as they redefine global timekeeping?
Could the quest for the world's most precise nuclear clock accidentally disrupt the supply of a critical life-saving cancer treatment?
The First Operational Thorium-229 Nuclear Clocks (2026): Physics, Applications, and the Race for Ultimate Precision
Overview
In October 2026, scientists at TU Wien and Tsinghua University announced the first operational thorium-229 nuclear clocks, marking a major breakthrough in timekeeping. These clocks use the thorium-229 nucleus, which has a uniquely low-energy state, allowing precise control with vacuum ultraviolet lasers. Because the atomic nucleus is about 100,000 times smaller than the electron shell and highly isolated from environmental disturbances, nuclear clocks promise unprecedented stability. Their sensitivity to changes in fundamental constants makes them powerful tools for probing dark matter. However, the technology faces challenges, including the extreme scarcity of thorium-229 and technical hurdles in crystal engineering and laser operation.