A cryogenic ion-trap apparatus for laser excitation of the Th-229 nuclear isomer

Thorium-229 hosts the only known nuclear transition with an excitation energy in the optical domain, enabling the prospect of a nuclear optical clock of unprecedented performance and sensitivity to new physics. While direct nuclear excitation and high resolution vacuum ultraviolet (VUV) spectroscopy has been achieved in thorium-doped crystals, realizing a nuclear clock of the highest accuracy requires isolating thorium atoms in an ion trap. We present our ongoing efforts to trap multiply charged ²²⁹Th³⁺ in an extremely high vacuum (XHV) cryogenic apparatus and excite the nuclear transition using a two-photon scheme that mitigates the technical challenges associated with VUV radiation. We discuss the evaluation of systematic uncertainties, including light shifts unique to this excitation scheme, and present our compact trap architecture that allows direct laser-ablation loading of multiply charged ions.