Gravitational Redshift Tests with Atomic Clocks and Atom Interferometers

TL;DR

This paper explores how atomic clocks and atom interferometers can test the gravitational redshift and the universality of matter-energy coupling to gravity, including potential violations of the equivalence principle, by analyzing their sensitivities and limitations.

Contribution

It provides a comprehensive quantum treatment of gravitational redshift tests using atomic systems, highlighting new configurations and mechanisms for enhanced sensitivity.

Findings

Trapped atomic clocks can detect non-linear potential contributions.

Modified atom interferometer setups can mimic gravitational redshift tests.

Internal atomic transitions enable light-pulse interferometers to test redshift violations.

Abstract

Atomic interference experiments can probe the gravitational redshift via the internal energy splitting of atoms and thus give direct access to test the universality of the coupling between matter-energy and gravity at different spacetime points. By including possible violations of the equivalence principle in a fully quantized treatment of all degrees of freedom, we characterize how the sensitivity to gravitational redshift violations arises in atomic clocks and atom interferometers, as well as their underlying limitations. Specifically, we show that: (i.) Contributions beyond linear order to trapping potentials lead to such a sensitivity of trapped atomic clocks. (ii.) While Bragg-type interferometers, even with a superposition of internal states, with state-independent, linear interaction potentials are at first insensitive to gravitational redshift tests, modified configurations, for example by relaunching the atoms, can mimic such tests tests under certain conditions. (iii.) Guided atom interferometers are comparable to atomic clocks. (iv.) Internal transitions lead to state-dependent interaction potentials through which light-pulse atom interferometers can become sensitive to gravitational redshift violations.