Optical Magnetometer that is Insensitive to Magnetic Fields and What is it Good for?

The Global Network of Optical Magnetometers for Exotic physics searches (GNOME) has been using optical magnetometers to search for dark matter interaction with fermionic spins. Upgrading our sensors to so-called self-compensating comagnetometers is expected to improve network sensitivity by up to 4 orders of magnitude. The new sensors are based on simultanuous spin-polarization of alkali metal and noble gas atoms enclosed in the single hot vapour cell. When the experimental conditions are carefully tuned, the nuclear polarization of the noble gas atoms acts as a magnetic shield for the alkali atoms resulting in significant attenuation of magnetic noises in the sensor readout. Following a brief introduction to dark matter searches and a description of the current GNOME status I will discuss the experimental setup and the principle of comagnetometer operation.