The positron is the antimatter counterpart of the electron, identical in mass but carrying an equal and opposite electric charge. Like the electron, it also behaves like a tiny bar magnet, and according to a key prediction of the Standard Model of particle physics, its magnetic moment should be exactly equal and opposite to the electron’s.

Through new research published in Physical Review Letters, Gerald Gabrielse and colleagues at Northwestern University in Illinois have unveiled a promising new way to test this assumption, by trapping a single positron in a “quantum cyclotron.”