Equivalence Principle and Gravitational Redshift

We investigate leading order deviations from general relativity that violate the Einstein equivalence principle in the gravitational standard model extension. We show that redshift experiments based on matter waves and clock comparisons are equivalent to one another. Consideration of torsion balance tests, along with matter-wave, microwave, optical, and Mössbauer clock tests, yields comprehensive limits on spin-independent Einstein equivalence principle-violating standard model extension terms at the ${10}^{-6}$ level.

Figure 1

Mach-Zehnder clock or atom interferometer. Two otherwise freely falling clocks (or halves of an atomic wave packet) receive momentum impulses that change their velocity by $\pm v_r$. The dashed lines indicate trajectories without gravity.