# Characterizing atomic magnetic gradiometers for fetal magnetocardiography

## TL;DR

This paper presents a new atomic magnetic gradiometer with high sensitivity and background suppression capabilities, enabling improved fetal magnetocardiography in challenging environments.

## Contribution

The development of a SERF vector atomic magnetic gradiometer with enhanced sensitivity, high CMRR, and a background suppression metric for optimal fetal heart signal detection.

## Key findings

- Sensitivity of 3 fT/cm/Hz^{1/2} achieved
- Common mode rejection ratio over 150
- Effective background suppression for fetal magnetocardiography

## Abstract

Atomic magnetometers (AMs) offer many advantages over superconducting quantum interference devices (SQUIDs) due to, among other things, having comparable sensitivity while not requiring cryogenics. One of the major limitations of AMs is the challenge of configuring them as gradiometers. We report the development of a spin-exchange relaxation free (SERF) vector atomic magnetic gradiometer with sensitivity of $3\, \rm{fT} \,{cm}^{-1}{Hz}^{-1/2}$ and common mode rejection ratio (CMRR) $> 150$ in the band from DC to 100 Hz. We introduce a background suppression figure of merit for characterizing the performance of gradiometers. It allows for optimally setting the measurement baseline, and for quickly assessing the advantage, if any, of performing a measurement in gradiometric mode. As an application, we consider the problem of fetal magnetocardiography (fMCG) detection in the presence of a large background maternal MCG signal.