First nuclear clock ticks with thorium-229
A nuclear clock synchronized to 229Th
Physicists have built the first nuclear clock by locking a vacuum-ultraviolet laser to a transition in thorium-229. Using a cadmium vapor source to generate 148.4-nm light and a home-grown 229Th:CaF2 crystal, they stabilized the laser to a narrow nuclear absorption line. The clock's frequency was reproducible across independently fabricated crystals, marking a shift from atomic electron transitions to the atomic nucleus for timekeeping.
Converting nuclear laser spectroscopy into clock operation requires combining, in a single system, a traceable narrow-linewidth VUV probe, a 229Th-containing reference and a high-bandwidth, high-signal-to-noise readout of weak nuclear response, together with a demonstration of nuclear-transition-frequency reproducibility in independently prepared references.