Description
Validating $\bf ^{176}$Lu$\bf ^{+}$ Optical Frequency References at the $\bf{10^{-19}}$ level
K. J. Arnold,∗ M. D. K. Lee, Qin Qichen, Qi Zhao, Zhao Zhang, and N. Jayjong
Centre for Quantum Technologies, NUS
M. D. Barrett
Centre for Quantum Technologies, NUS and Department of Physics, NUS
The $^{176}\text{Lu}^+$ $^1\text{S}_0 \rightarrow {}^3\text{D}_1$ transition serves as a robust frequency reference due to its low sensitivity to blackbody radiation and electromagnetic perturbations, allowing for high-accuracy operation at room temperature without extensive shielding [1]. Building on recent advances in micromotion control [2], quadrupole shift assessment [3], and studies of background gas collision effects [4], we report a comprehensive evaluation of two independent $^{176}\text{Lu}^+$ single-ion optical frequency references, achieving total systematic uncertainties of $1.1 \times 10^{-19}$ and $1.4 \times 10^{-19}$ [5]. The two systems were directly compared using correlation spectroscopy with Ramsey times of up to 10 seconds, yielding a measurement instability of $4.8 \times 10^{-16}(\tau/s)^{-1/2}$. After 200 hours of averaging, the clocks demonstrated a relative frequency agreement of $[-2.4 \pm (5.7)_{\text{stat}} \pm (1.0)_{\text{sys}}] \times 10^{-19}$ [5]. While other individual clocks have reported assessed uncertainties below $10^{-18}$, this work represents the first demonstrated agreement of optical clock performance with total uncertainty below this level. These results open the way for new applications in millimeter-scale relativistic geodesy and tests of fundamental physics at the $10^{-19}$ frontier of accuracy.
[1] K. Arnold, R. Kaewuam, A. Roy, T. Tan, and M. Barrett,
Nature communications 9 (2018).
[2] K. Arnold, N. Jayjong, M. Kang, Q. Qichen, Z. Zhang,
Q. Zhao, and M. Barrett, Physical Review A 110, 033115
(2024).
[3] M. Lee, Q. Zhao, Q. Qichen, Z. Zhang, N. Jayjong,
K. Arnold, and M. Barrett, Physical Review A 113,
012805 (2026).
[4] M. Barrett and K. Arnold, arXiv preprint
arXiv:2512.05474 (2025).
[5] K. Arnold, M. Lee, Z. Qi, Q. Qin, Z. Zhao, N. Jayjong,
and M. Barrett, arXiv preprint arXiv:2512.07346 (2025).