Absolute frequency measurement of a Lu$^+$ $(^{3}\rm D_1)$ optical frequency standard via link to international atomic time

Abstract: We report on an absolute frequency measurement of the ${\rm Lu}^{+}\,(^{3}\rm D_1)$ standard frequency which is defined as the hyperfine-average of $^{1}\rm S_0$ to $^{3}\rm D_1$ optical clock transitions in $^{176}{\rm Lu}^{+}$. The measurement result of $353\,638\,794\,073\,800.35(33)$Hz with a fractional uncertainty of $9.2 \times 10^{-16}$ was obtained by operating a single-ion $^{176}{\rm Lu}^{+}$ frequency standard intermittently over 3 months with a total uptime of 162 hours. Traceability to the International System of Units (SI) is realized by remote link to International Atomic Time. This is the first reported absolute frequency value for a ${\rm Lu}^{+}\,(^{3}\rm D_1)$ optical frequency standard.