Optical clock frequency ratios with uncertainty ≤ 3.2 × 10^−18

Published

January 6, 2026

Author(s)

Alexander Aeppli, Willa Arthur-Dworschack, Kyle Beloy, Caitlin Berry, Tobias Bothwell, Angela Folz, Tara Fortier, Tanner Grogan, Youssef Hassan, Zoey Zimeng Hu, David Hume, Benjamin Hunt, Kyungtae Kim, Amanda Koepke, Dahyeon Lee, David Ray Leibrandt, Ben Lewis, Andrew Ludlow, Mason Marshall, Nicholas Nardelli, Harikesh Ranganath, Daniel Rodriguez Castillo, Jeffrey Sherman, Jacob Siegel, Suzanne Thornton, William Warfield, Jun Ye

Abstract

We report high-precision frequency ratio measurements between optical atomic clocks based on 27Al+, 171Yb, and 87Sr. With total fractional uncertainties at or below 3.2 × 10−18, these measurements meet the milestone criteria for redefinition of the second in the International System of Units. Discrepancies in 87Sr ratios at 1 × 10−16 and the Al+/Yb ratio at 1.5 × 10−17 in fractional units compared to our previous measurement underscore the importance of repeated, high-precision comparisons by different laboratories. A key innovation in this work is the use of a common ultrastable reference delivered to all clocks via a 3.6 km phase-stabilized fiber link between the institutions. Derived from a cryogenic single-crystal silicon cavity, this reference improves comparison stability by a factor of 2 to 3 over previous systems, with an optical lattice clock ratio achieving a fractional instability of 1.3×10−16 at 1 second. By enabling faster comparisons, this stability will improve sensitivity to non-white noise processes and other underlying limits of state-of-the-art optical frequency standards.

Citation

arXiv

Pub Type

Journals

Keywords

atomic clocks, time and frequency, metrology, precision measurement, atomic clock frequency ratios, atomic, molecular, and optical physics

Citation

Aeppli, A. , Arthur-Dworschack, W. , Beloy, K. , Berry, C. , Bothwell, T. , Folz, A. , Fortier, T. , Grogan, T. , Hassan, Y. , Hu, Z. , Hume, D. , Hunt, B. , Kim, K. , Koepke, A. , Lee, D. , Leibrandt, D. , Lewis, B. , Ludlow, A. , Marshall, M. , Nardelli, N. , Ranganath, H. , Rodriguez Castillo, D. , Sherman, J. , Siegel, J. , Thornton, S. , Warfield, W. and Ye, J. (2026), Optical clock frequency ratios with uncertainty ≤ 3.2 × 10^−18, arXiv (Accessed January 8, 2026)