Observation of the $^1$S$_0$ to $^3$D$_1$ clock transition in   $^{175}$Lu$^+$
  We report the first laser spectroscopy of the $^1$S$_0$ to $^3$D$_1$ clock transition in $^{175}$Lu$^+$. Clock operation is demonstrated on three pairs of Zeeman transitions, one pair from each hyperfine manifold of the $^3$D$_1$ term. We measure the hyperfine intervals of the $^3$D$_1$ to 10 ppb uncertainty and infer the optical frequency averaged over the three hyperfine transitions to be 353.639 915 952 2 (6) THz. The lifetime of the $^3$D$_1$ state is inferred to be $174^{+23}_{-32}$ hours from the M1 coupling strength. 
Kyle J. Arnold, R. Kaewuam, A. Roy, E. Paez, S. Wang, M. D. Barrett
physics.atom-ph physics.optics quant-ph