This thesis documents the first realization of a nuclear clock, a promising next-generation platform for precision metrology and fundamental physics, based on a 8.4 eV transition in thorium-229. Using a vacuum ultraviolet frequency comb developed by the author, the narrow 229Th nuclear clock transition in a solid-state CaF2 host crystal was studied in high resolution spectroscopy, resulting in quantum state resolution to reveal the underlying nuclear structure and establishment of a direct frequency connection between the nuclear clock and an optical atomic clock. This work marks the start of nuclear-based solid-state optical clocks and demonstrates the first comparison of nuclear and atomic clocks for fundamental physics studies. The thesis represents a remarkable convergence of precision metrology, ultrafast strong-field physics, nuclear physics, and fundamental physics. The key results that comprise this thesis are: the unprecedented precision achieved for the measurement of the narrow nuclear transition (~100 kHz linewidth, ~600 s lifetime, and absolute frequency determination to 12 significant digits); a spectrum of nuclear quadrupole splitting peaks, and the direct determination of the ratio of quadrupole moments between the ground and isomeric states; and the detailed description and characterization of the world’s unique high resolution VUV frequency comb.

Chuankun Zhang received his PhD in 2025 from JILA, a joint institute of NIST and the University of Colorado Boulder, under the supervision of Jun Ye. His doctoral research focused on developing a nuclear clock using a VUV frequency comb. He is currently an IQIM Postdoctoral Scholar in Andrei Faraon’s group at Caltech, where he works on quantum-network technologies using rare-earth dopants in solids.