Electron magnetic moment from geonium spectra: Early experiments and background concepts

Abstract

The magnetic moment of a free electron has been measured by observing both its low-energy spin and cyclotron resonances (at ${\nu }_s$=${\omega }_s$/2π and ${\nu }_c$=${\omega }_c$/2π, respectively) by means of a sensitive frequency-shift technique. Using radiation and tuned-circuit damping of a single electron, isolated in a special anharmonicity-compensated Penning trap, also cooled to 4 K, the electron’s motion is brought nearly to rest, thus preparing it in a cold quasipermanent state of the geonium ‘‘atom.’’ The magnetic-coupling scheme, described as a continuous Stern-Gerlach effect, is made possible through a weak Lawrence magnetic bottle which causes the very narrow axial resonance, at ${\nu }_z$=${\omega }_z$/2π for the harmonically bound electron, to change in frequency by a small fixed amount δ per unit change in magnetic quantum number.