Measurement of a false electric dipole moment signal from $^{199}$Hg atoms exposed to an inhomogeneous magnetic field

TL;DR

This study measures a false electric dipole moment signal in $^{199}$Hg atoms caused by magnetic field gradients, which mimics an EDM but is P- and T-conserving, using a neutron magnetic resonance spectrometer.

Contribution

It provides the first detailed measurement and analysis of a false EDM signal arising from magnetic field inhomogeneities in mercury atoms.

Findings

The measured frequency shift matches theoretical predictions.

The effect is P- and T-conserving, unlike true EDM signals.

Results improve understanding of systematic effects in EDM experiments.

Abstract

We report on the measurement of a Larmor frequency shift proportional to the electric-field strength for $^{199}{\rm Hg}$ atoms contained in a volume permeated with aligned magnetic and electric fields. This shift arises from the interplay between the inevitable magnetic field gradients and the motional magnetic field. The proportionality to electric-field strength makes it apparently similar to an electric dipole moment (EDM) signal, although unlike an EDM this effect is P- and T-conserving. We have used a neutron magnetic resonance EDM spectrometer, featuring a mercury co-magnetometer and an array of external cesium magnetometers, to measure the shift as a function of the applied magnetic field gradient. Our results are in good agreement with theoretical expectations.