Overview
- Researchers published two Nature papers on Wednesday, October 7, 2026, reporting independent prototype nuclear clocks built in Vienna (TU Wien/PTB) and Beijing (Tsinghua).
- Both devices use the rare isotope thorium-229 embedded in calcium fluoride crystals and are driven by narrow-linewidth ultraviolet lasers that lock the laser frequency to a nuclear transition at about 148 nm.
- The Vienna/PTB prototype demonstrated a precision near 10⁻15 (about one second every 30 million years) and was used in an initial search for ultralight scalar dark matter that set limits without detecting a signal.
- The Tsinghua/Beijing prototype showed roughly six times better short-term stability in early tests, but neither clock yet beats the best optical atomic clocks.
- Key technical hurdles remain: observed nuclear resonance linewidths are around 30 kHz versus the expected sub-hertz natural linewidth, thorium-229 supply is scarce, and teams plan upgrades in crystal quality, UV laser power, and alternative trapped‑ion designs to improve accuracy.