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

TL;DR

The new measurement has an uncertainty that is about six times smaller, and it shifts the values by 1.7 standard deviations, so the lowest quantum levels of the spin and cyclotron motion are resolved, and the cycle frequencies as well as spin frequencies are determined using quantum jump spectroscopy.

Abstract

A measurement using a one-electron quantum cyclotron gives the electron magnetic moment in Bohr magnetons, g/2 = 1.001 159 652 180 73 (28) [0.28 ppt], with an uncertainty 2.7 and 15 times smaller than for previous measurements in 2006 and 1987. The electron is used as a magnetometer to allow lineshape statistics to accumulate, and its spontaneous emission rate determines the correction for its interaction with a cylindrical trap cavity. The new measurement and QED theory determine the fine structure constant, with alpha^{-1} = 137.035 999 084 (51) [0.37 ppb], and an uncertainty 20 times smaller than for any independent determination of alpha.

Figures (5)

• Figure 1: Most accurate measurements of the electron $g/2$ (a), and most accurate determinations of $\alpha$ (b).
• Figure 2: Cylindrical Penning trap cavity used to confine a single electron and inhibit spontaneous emission.
• Figure 3: Electron's lowest cyclotron and spin levels.
• Figure 4: Quantum-jump spectroscopy lineshapes for cyclotron (left) and anomaly (right) transitions, with maximum likelihood fits to broadened lineshape models (solid), and inset resolution functions. Vertical lines show the 1-$\sigma$ uncertainties for extracted resonance frequencies. Corresponding un-broadened lineshapes are dashed. Gray bands indicate 68% confidence limits for distributions about broadened fits.
• Figure 5: Modes of the trap cavity are observed with synchronized electrons (a) HarvardMagneticMoment2006, as well as with a single electron damping rate $\gamma_0$ (b) and its amplitude dependence $\gamma_2$ (c). Offset of $g/2$ from our result in Eq. \ref{['eq:g']} without (open circle) and with (points) cavity-shift corrections, with an uncertainty band for the average (d).