Systematic errors in high-precision gravity measurements by light-pulse atom interferometry on the ground and in space

TL;DR

This paper identifies a systematic linear error in high-precision gravity measurements using light-pulse atom interferometry, which impacts experiments in space and ground-based geodesy, gravitational constant measurement, and gravitational wave detection.

Contribution

It reveals a previously unnoticed systematic error in atom interferometry measurements caused by limited data points per drop, affecting various fundamental physics experiments.

Findings

The gravity gradient effect is systematically overestimated due to measurement limitations.

The error cancels out when testing the universality of free fall with isotopes using a single laser.

Different atomic species and laser frequencies introduce large phase shift differences even without violations.

Abstract

We focus on the fact that light-pulse atom interferometers measure the atoms' acceleration with only three data points per drop. As a result, the measured effect of the gravity gradient is systematically larger than the true one, an error linear with the gradient and quadratic in time almost unnoticed so far. We show how this error affects the absolute measurement of the gravitational acceleration $g$ as well as ground and space experiments with gradiometers based on atom interferometry such as those designed for space geodesy, the measurement of the universal constant of gravity and the detection of gravitational waves. When atom interferometers test the universality of free fall and the weak equivalence principle by dropping different isotopes of the same atom one laser interrogates both isotopes and the error reported here cancels out. With atom clouds of different species and two lasers of different frequencies the phase shifts measured by the interferometer differ by a large amount even in absence of violation. Systematic errors, including common mode accelerations coupled to the gravity gradient with the reported error, lead to hard concurrent requirements --on the ground and in space-- on several dimensionless parameters all of which must be smaller than the sought-for violation signal.