# Application of Spin-Exchange Relaxation-Free Magnetometry to the Cosmic Axion Spin Precession Experiment

## TL;DR

This paper explores using a SERF magnetometer with high sensitivity for detecting axion-induced nuclear spin precession in the CASPEr experiment, addressing dynamic range limitations with flux transformers.

## Contribution

It demonstrates a highly sensitive SERF magnetometer suitable for CASPEr and proposes a flux transformer method to overcome dynamic range constraints.

## Key findings

- Achieved sensitivity of approximately 1 fT/√Hz with the SERF magnetometer.
- Identified the limited dynamic range of SERF magnetometers as a challenge.
- Suggested flux transformer technique to extend dynamic range for higher axion frequencies.

## Abstract

The Cosmic Axion Spin Precession Experiment (CASPEr) seeks to measure oscillating torques on nuclear spins caused by axion or axion-like-particle (ALP) dark matter via nuclear magnetic resonance (NMR) techniques. A sample spin-polarized along a leading magnetic field experiences a resonance when the Larmor frequency matches the axion/ALP Compton frequency, generating precessing transverse nuclear magnetization. Here we demonstrate a Spin-Exchange Relaxation-Free (SERF) magnetometer with sensitivity $\approx 1~{\rm fT/\sqrt{Hz}}$ and an effective sensing volume of 0.1 $\rm{cm^3}$ that may be useful for NMR detection in CASPEr. A potential drawback of SERF-magnetometer-based NMR detection is the SERF's limited dynamic range. Use of a magnetic flux transformer to suppress the leading magnetic field is considered as a potential method to expand the SERF's dynamic range in order to probe higher axion/ALP Compton frequencies.