Atom-Interferometry Measurement of the Fine Structure Constant

Using an atom interferometer to measure the quotient of the reduced Planck's constant and the mass of a cesium-133 atom h/m(Cs), the most accurate measurement of the fine structure constant alpha = 1/137.035999046(27) is recorded, at an accuracy of 0.20 parts per billion (ppb). Using multiphoton interactions (Bragg diffraction and Bloch oscillations), the largest phase (12 million radians) of any Ramsey-Borde interferometer and controlled systematic effects at a level of 0.12 ppb are demonstrated. Comparing the Penning trap measurements with the Standard Model prediction of the electron gyromagnetic anomaly a(e) based on the a measurement, a 2.5 sigma tension is observed, rejecting dark photons as the reason for the unexplained part of the muon's gyromagnetic moment discrepancy at a 99% confidence level according to frequentist statistics. Implications for dark-sector candidates (e.g., scalar and pseudoscalar bosons, vector bosons, and axial-vector bosons) may be a sign of physics beyond the Standard Model. A future upgrade of the cesium fountain atom interferometer is also proposed to increase the accuracy of h/m(Cs) by 1 to 2 orders of magnitude, which would help resolve the tension.