Our group plans to join the GNOME project. To date, this international collaboration lacks a magnetometer in the southern hemisphere. We have the parts required to build one, the task will be to assemble the parts, characterise the performance of the device and then attach the magnetic field readout to a GPS synchronised data logger to compare with other devices in the global network.
An Rb atomic magnetometer works by shining a laser beam through a gas cell containing some Rb atoms. When properly prepared, the Rb vapour is sensitive to the magnetic field. A change in the magnetic field will induce a shift in the polarisation of the light that passes through the gas cell. To measure the magnetic field, therefore, all we have to do is measure the polarisation of the light that has interacted with the atoms.
Atomic magnetometers are ultra-sensitive devices. They can measure fields at the femto-Tesla level, which is about 40 billion times weaker than the Earth magnetic field. Unlike SQUID sensors, atomic magnetometers work at room temperature.
To use a magnetometer for GNOME, you have to avoid accidentally measuring a magnetic field since you are actually looking for something quite different! So, the experiment is heavily shielded and uses an atomic transition that is insensitive to magnetic fields. The thing you are looking for is actually exotic spin coupling with an axion-like field. This field is a proposed dark matter candidate. The GNOME network will place limits on the coupling strength and therefore limits on the plausibility of this proposed field.