Josephson Junction Yields Fundamental Constants

The first low‐temperature physics experiment to determine a fundamental constant has yielded new values for e/h (ratio of electron charge to Planck's constant) and α (fine‐structure constant). Until now the most reliable determination of α has utilized measurements by Willis Lamb, Sol Triebwasser and Edward Dayhoff on the fine‐structure splitting in deuterium; the value is $1/137.0388±0.0006.$ The new experiments (reported in the 20 Feb. issue of Phys. Rev. Letters), which use the ac Josephson effect to measure e/h directly, when combined with the measured values of other fundamental constants, yield for α the value $1/137.0359±0.0004.$ This new value may remove the discrepancy between theoretical and experimental values for the hyperfine splitting in hydrogen.