A single-beam, potassium SERF magnetometer for the Global Network of Optical Magnetometers to search for Exotic physics (GNOME).

Ultralight axion-like particles are a candidate for dark matter. These particles can form topological defects that can be detected through their coupling with the spins of elementary particles. This coupling results in a pseudo-magnetic interaction. The Global Network of Optical Magnetometers to search for Exotic physics (GNOME) searches for transient signals caused by the Earth going through these topological defects using several magnetometers located throughout the world to differentiate true signals from false positives. At Oberlin College, we have developed a single-beam spin exchange relaxation-free (SERF) magnetometer using potassium atoms with a helium buffer gas. We look at the absorption of circularly polarized light going through the vapor cell housed within four layered magnetic shields. The magnetic field dependence of the absorption is used to measure the magnetic field. We present the characterization of our magnetometer and discuss the development of a future co-magnetometer with improved sensitivity.