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arXiv · 2607.07044

Absolute frequency measurement of the $^{176}$Lu$^+\,(^{3}\mathrm{D}_1)$ standard against the NRC-FCs2 fountain with $2.6\times10^{-16}$ uncertainty

K. J. Arnold·Bin Jian·Zhao Zhang·Qi Zhao·Qin Qichen·N. Jayjong·M. D. K. Lee·Scott Beattie·M. D. Barrett
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Abstract

We report an improved absolute frequency measurement of the $^{176}$Lu$^+\,(^{3}\mathrm{D}_1)$ optical frequency standard, evaluated via a remote link to the NRC-FCs2 caesium fountain primary frequency standard. Operating a single ion clock with 94.2% uptime over 10 days, and using an ambiguity-resolved precise point positioning (PPP-AR) link over the Global Positioning System (GPS), we determine an absolute frequency of $353\,638\,794\,073\,800.33(9)\,$Hz at a fractional uncertainty of $2.6 \times 10^{-16}$. This agrees with our previous result, which underpins the CIPM recommended frequency value, and reduces the uncertainty by a factor of 3.6.

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K. J. Arnold, Bin Jian, Zhao Zhang, Qi Zhao, Qin Qichen, N. Jayjong, M. D. K. Lee, Scott Beattie, M. D. Barrett. 2026-07-08. Absolute frequency measurement of the $^{176}$Lu$^+\,(^{3}\mathrm{D}_1)$ standard against the NRC-FCs2 fountain with $2.6\times10^{-16}$ uncertainty. https://arxiv.org/abs/2607.07044

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