A nuclear clock synchronized to (229)Th.

A nuclear clock based on 229Th achieves a fractional frequency instability of 5 × 10-13/τ/s, demonstrating a new level of precision in solid-state timekeeping.

• Why it matters: Precise time measurement is essential for fundamental physics tests and advanced technologies, but current atomic clocks face limitations in compactness and robustness, prompting the need for alternative nuclear-based standards.
• What they did: The team stabilized a 148.4 nm VUV laser to a nuclear transition in 229Th:CaF2 crystals using four-wave mixing and frequency modulation absorption readout, creating a stable nuclear clock.
• The result: This work confirms laser-addressed nuclei as reliable clock references, enabling the development of compact nuclear clocks, quantum sensors, and enhanced tests of fundamental physics.