World's first working nuclear clocks built with thorium-229

Two independent teams in Vienna and Beijing have built prototype nuclear clocks based on thorium-229, using laser-tuned transitions inside the nucleus instead of electron jumps. The results were published in Nature; the Chinese clock is about six times more stable than the Vienna one but still trails cesium atomic standards.

• Prototypes built at Vienna University of Technology and Tsinghua University in Beijing
• Clocks use a laser tuned to thorium-229 nucleus transitions between two energy states
• Chinese version is roughly 6 times more stable than the Vienna clock
• Current drift is about 1 second per 30 million years, 10 times worse than cesium standards