A nuclear clock synchronized to 229 Th
This work demonstrates a nuclear clock using 229Th, leveraging its unique low-lying isomeric transition accessible by VUV lasers. The team developed a continuous-wave VUV source, a compact 229Th crystal platform, and fast phototube spectroscopy for frequency discrimination. They achieved a projected fractional frequency instability of $7 imes 10^{-12}$ and demonstrated reproducibility across different crystal types.