Electromagnetic cavity tests of Lorentz invariance on Earth and in space

TL;DR

This paper reports a high-precision Michelson-Morley type experiment testing the isotropy of light speed using cryogenic sapphire and ultra-low-expansion glass cavities, setting new upper limits on anisotropy.

Contribution

It introduces a novel experimental setup combining cryogenic sapphire and ultra-low-expansion glass cavities for testing Lorentz invariance.

Findings

Upper limit for anisotropy of light in sapphire: Δc/c < 1 x 10^-16

Frequency stability limited the measurement precision

Demonstrates feasibility of space-based optical cavity tests

Abstract

We present a Michelson-Morley type experiment for testing the isotropy of the speed of light in vacuum and matter. The experiment compares the resonance frequency of an actively rotated monolithic optical cryogenic sapphire resonator against the resonance frequency of a stationary evacuated optical cavity made of ultra-low-expansion glass. The results yield an upper limit for the anisotropy of the speed of light in matter (sapphire) of Delta(c)/c < 1 x 10^-16, limited by the frequency stability of the sapphire resonator.