Clocks based on hyperfine and electronic transitions in laser-cooled atoms, with fractional inaccuracy and instability now reaching below 1e-18, have revolutionized positioning, navigation, and timekeeping (PNT) and serve as one of the experimental foundations on which the Standard Model of particle physics is built. A new type of clock based on the internal transitions of atomic nuclei, dubbed nuclear clocks, was proposed by Peik and Tamm in 2003. Among nuclei, the thorium-229 nucleus is unique in having a transition at low enough energy to be accessible with present-day laser technology, and laser spectroscopy of the 148 nm thorium-229 nuclear isomer transition was first demonstrated by three groups nearly simultaneously in 2024. Due to the higher energy scales and additional fundamental interactions present in the nucleus, nuclear transitions are much more sensitive to small deviations from the predictions of the Standard Model than atomic transitions. Thus, thorium nuclear clocks may offer insights about unification theories, the nature of dark matter, or other physics beyond the Standard Model.

I will begin this talk with a brief overview of the thorium-229 nuclear isomer transition and the two experimental approaches currently being pursued to build thorium nuclear clocks: one based on thorium doped into solid-state hosts and the other based on trapped and laser-cooled thorium ions. Next, I will present the design and current status of a trapped-ion thorium clock experiment under construction in my lab at UCLA. Finally, I will conclude with a discussion of the fundamental physics reach of this and other thorium nuclear clocks.

Bio: David Leibrandt is a Professor in the Department of Physics & Astronomy at UCLA. Prior to moving to UCLA in 2022, he led the trapped-ion optical atomic clock and precision measurement experiments within the Ion Storage Group at the National Institute of Standards and Technology in Boulder, CO. He received his Ph.D. in Physics from the Massachusetts Institute of Technology (MIT) in 2009 and his B.S.E. in Engineering Physics from the University of Michigan in 2004. David is a Fellow of the American Physical Society and a recipient of the EFTF Young Scientist Award and the Department of Commerce Gold Medal Award for the development of optical atomic clocks based on quantum-logic spectroscopy of aluminum ions with record fractional inaccuracy below 1e-18.