Direct VUV Laser Search for the $^{229}$Th Transition

The nucleus of $^{229}$Th has an exceptionally low-energy isomeric transition in the vacuum-ultraviolet (VUV) spectrum around 8.338(24) eV [1] that, if measured with spectroscopic precision, holds much promise for future timekeeping and quantum logic operations. Our group has pursued the development of thorium-doped crystals [2], both as a way to search for the transition, as well as a potential platform for a solid state nuclear clock. Here we will present the results of an ongoing direct VUV laser search for the isomeric transition, during which fluorescence has been observed that may provide evidence of optical driving and quenching of the nuclear transition in the crystal environment. Possible interpretations will be discussed.

[1] Kraemer, S., et. al. Observation of the radiative decay of the ²²⁹Th nuclear clock isomer. Nature (2023).

[2] Tkalya, E. V. et al.: Phys. Rev. C 92, 054324 (2015)