Precision 10∶1 capacitance ratio measurement using a Josephson impedance bridge

Josephson impedance bridges have been reported to provide uncertainties close to that from the best conventional bridges when comparing 1:1 impedance ratios. For a 10:1 capacitance ratio (100 pF to 10 pF) a type A uncertainty accuracy of a few parts in 10⁷ has been achieved with 1-V programmable Josephson arrays. The accuracy can be significantly improved when using 10-V Josephson arrays. Preliminary measurements are also presented with type A uncertainties at the level of parts in 10⁸ (k = 1).