Test of Einstein Equivalence Principle by frequency comparisons of optical clocks

TL;DR

This paper proposes a novel method using high-precision optical clock comparisons to test Einstein's Equivalence Principle and constrain violations predicted by the standard model extension, achieving significant limits with existing experiments.

Contribution

It introduces a new frequency comparison scheme with optical clocks to simultaneously test the weak equivalence principle and gravitational redshift, providing tighter constraints on Lorentz violation.

Findings

Determined Earth-dependent parameter β_E at 10^{-5} level.

Measured clock-dependent parameter ξ_Sr at 10^{-5} level.

Set limits on Lorentz violation coefficients in standard model extension.

Abstract

The Einstein Equivalence Principle (EEP) carries a pivotal role in understanding theory of gravity and spacetime. It guarantees the gravity to be understood as geometric phenomenon. Considering gravitational coupling of matter in the standard model extension, we propose a novel scheme using frequency measurements to limit the equivalence principle violations in normal matter. The proposal consists of the comparison of high-precision clocks, comoving with the freely falling frame. The experimental comparison of identical kind of clocks on Earth surface can be used to carry out the proposed test, which allows performing simultaneous tests of weak equivalence principle and gravitational redshift. From the existing experiments of Sr optical clocks, we present a simultaneous determination of Earth-dependent parameter $\beta_{\text{E}}$ and clock-dependent parameter $\xi_{\text{Sr}}$ at the level of $10^{-5}$, and in combination with the gravitational redshift experiments and lunar laser ranging, we also obtain a limit on standard model extension coefficients for Lorentz violation. This work provides another important fundamental physics application for the continuous-improvement accuracy of atomic or optical clocks.