European Conference on Trapped Ions (ECTI)

Singly ionized lutetium (${}^{176}$Lu${}^{+}$) has a unique level structure that provides multiple clock transitions. In combination with hyperfine averaging, two of these transitions (${}^1{S}_0$ – ${}^3{D}_1$ & ${}^1{S}_0$ – ${}^3{D}_2$) present both a long lifetime and low sensitivity to the electromagnetic environment, which allows high performance clock operation on both transitions. Recently we have demonstrated clock comparison on the ${}^1{S}_0$ – ${}^3{D}_1$ at the low ${10}^{-18}$ level limited by clock stability, with an error budget that supports the capability to go well beyond ${10}^{-18}$.

The relative ease at which we are able to establish agreement between two independent frequency references is attractive both for applications and establishing a laboratory frequency reference. We discuss the advantages that lutetium offers with an emphasis on the unique possibilities afforded by the existence of two transitions within the one system. In particular, a frequency ratio measured within the one system provides an independent metric that can validate performance claims made on a single transition.