A solid-state nuclear clock based on VUV absorption spectroscopy of ${}^{229}$Th

Abstract

We demonstrate sustained operation of a solid-state thorium-229 nuclear clock using continuous-wave absorption at 148.4 nm. In a ${}^{229}\mathrm{Th}:{\mathrm{CaF}}_2$ crystal, we resolve four quadrupole components of the D center and a broader O-center resonance. Feedback on the strongest narrow component is updated approximately every 10 s and remains active throughout a 30-h record. A hydrogen-maser-referenced frequency comb measures the output. Its fractional frequency instability follows approximately $1.29\times 10^{-11}(\tau /\mathrm{s}{)}^{-1/2}$ and reaches $1.24\times 10^{-13}$ at $10^4$ s. A separate 6.6-h run demonstrates feedback on a second quadrupole component. These measurements connect the resolved absorption spectra with sustained nuclear-clock operation and frequency comparisons between crystal segments.

12 pages total (5-page main manuscript and 7-page Supplemental Material), 3 figures