Atom Interferometers and the Gravitational Redshift

TL;DR

This paper critically examines claims that atom interferometers can test gravitational redshift at the Compton frequency, arguing they cannot, and proposes a new experiment to measure the effect.

Contribution

It clarifies that atom interferometers do not function as clocks at the Compton frequency and proposes a novel experiment to test gravitational redshift.

Findings

Atom interferometers are not equivalent to clocks ticking at the Compton frequency.

Previous experiments do not provide sensitive tests of gravitational redshift.

A new interferometric experiment is proposed to measure gravitational redshift.

Abstract

From the principle of equivalence, Einstein predicted that clocks slow down in a gravitational field. Since the general theory of relativity is based on the principle of equivalence, it is essential to test this prediction accurately. Muller, Peters and Chu claim that a reinterpretation of decade old experiments with atom interferometers leads to a sensitive test of this gravitational redshift effect at the Compton frequency. Wolf et al dispute this claim and adduce arguments against it. In this article, we distill these arguments to a single fundamental objection: an atom is NOT a clock ticking at the Compton frequency. We conclude that atom interferometry experiments conducted to date do not yield such sensitive tests of the gravitational redshift. Finally, we suggest a new interferometric experiment to measure the gravitational redshift, which realises a quantum version of the classical clock "paradox".