Precise determination of h/ me using a rotating, superconducting ring

Abstract

A precise determination of h/${m}_{e}$ (Planck's constant divided by the free-electron mass) using a rotating, superconducting ring is in progress. The measurement is based on flux quantization and the London moment---two manifestations of the macroscopic quantum nature of superconductivity. Here we report the first results from a precision, thin-film niobium ring. These data have a statistical error of 10 parts per million (ppm). A systematic error exists at the level of 2500 ppm, due to the presence of electric charge on the rotor. A model for the charge distribution is suggested and used to adjust the results and obtain a value of h/${m}_{e}$. This work has determined h/${m}_{e}$ directly to an accuracy of 100 ppm, a higher level of precision than previously reported. Recent theoretical calculations have predicted a relativistic mass increase of 150 ppm for electrons in superconducting niobium, but the uncertainty in our final results prevented the clear identification of this effect.

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