Abstract
We compare two optical clocks based on the electric quadrupole (E2) and the electric octupole (E3) transition of and measure the frequency ratio , improving upon previous measurements by an order of magnitude. Using two caesium fountain clocks, we find , the most accurate determination of an optical transition frequency to date. Repeated measurements of both quantities over several years are analyzed for potential violations of local position invariance. We improve by factors of about 20 and 2 the limits for fractional temporal variations of the fine structure constant to and of the proton-to-electron mass ratio to . Using the annual variation of the Sun’s gravitational potential at Earth , we improve limits for a potential coupling of both constants to gravity, and .
- Received 13 October 2020
- Revised 23 November 2020
- Accepted 15 December 2020
DOI:https://doi.org/10.1103/PhysRevLett.126.011102
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society