New Measurement of the Electron Magnetic Moment and the Fine Structure Constant

A new measurement resolves the cyclotron and spin levels for a single‐electron quantum cyclotron to obtain a dimensionless electron magnetic moment, g, to 7.6 parts in 10¹³ (nearly six times better than in the past) and shifted by 1.7 standard deviations. The new g, with a quantum electrodynamics (QED) calculation, determines the fine structure constant with a 0.7 ppb uncertainty — ten times smaller than for atom‐recoil determinations. Remarkably, this 100 mK measurement probes for internal electron structure at 130 GeV.