A Thorium-229 nuclear clock for precision metrology and fundamental physics

Optical atomic clocks, based on measurement and control of electronic states in atoms, are used to perform the most precise time/frequency metrology today and provide deep insights to fundamental physics. Recently, we extended precision laser spectroscopy to a low-energy nuclear isomeric state in thorium-229 for building a nuclear clock. Using a frequency comb laser source in the vacuum-ultraviolet (VUV), we coherently excite the thorium nuclear clock transition in solid state crystalline hosts. The nuclear excitation frequency is directly linked to today's most precise atomic clock using strontium-87. We resolve the individual nuclear quantum states and characterize state-dependent systematic clock frequency shifts with respect to temperature and doping concentration. The nuclear clock promises a portable solid-state platform with high stability and reproducibility for metrology applications. Precision nuclear spectroscopy also allows us to quantify the high sensitivity in nuclear-atomic clock comparisons for new physics beyond the Standard Model.