Geonium atom

A geonium atom is a useful "atomic system" created in a magnetic Penning trap, named so because it is bound to the Earth. A Penning trap is a combination of a homogeneous magnetic field and an electrostatic quadrupole potential. A single charged particle can be trapped indefinitely. Hans Dehmelt of the University of Washington created the first geonium atom in 1973, stably trapping an electron.