Ultracold atomic comagnetometer joins the search for dark matter

A device will use the ‘fifth state of matter’ to search for axions, a relatively neglected candidate for dark matter. The ‘comagnetometer’ consists of two extremely sensitive magnetic-field detectors made from rubidium-87 atoms. The atoms are cooled to near absolute zero to create a Bose–Einstein condensate, so each essentially acts as a single atom. Because they have different spin states that respond differently to magnetic fields, any variation measured by the two detectors could signal the presence of axions.