Accurate measurements of quantum voltage steps on arrays of bicrystal Josephson junctions

Abstract

Quantum voltages of an array of YBa2Cu3O7 bicrystal junctions were calibrated against a programmable Josephson array voltage standard. We demonstrated that steps of the current–voltage characteristic of an array of bicrystal junctions at voltages of about 9 mV were flat over the current range of about 80 μA to within six parts in 108. The coincidence of quantum voltages on the array of high-temperature superconductor junctions at 64 K and the reference voltage on the array of niobium junctions at 4.2 K was measured with an uncertainty of two parts in 108. With the same uncertainty, we revealed the coincidence of the Josephson constant KJ≡h/2e in YBa2Cu3O7 and in metallic superconductors.