Co-Operative External Synchronization in Josephson Series Arrays for the Cryogenic Voltage Standard

Abstract

The modern cryogenic Josephson array voltage standard takes advantage of two important principles. The first one is to use highly hysteretic Josephson junctions with overlapping Shapiro steps near zero current bias. This allows to obtain a stable quantized reference voltage in the volt region without an individual dc biasing of each junction. The second principle is to integrate the Josephson junctions into a superconducting microwave transmission line. This proves as an effective method to achieve a nearly uniform rf excitation of a very large number of junctions essential for a maximum voltage output² . In the last few years these two principles were successfully be used to realize Josephson arrays and, finally, a quantized voltage level of about 12 V was reached³ . In the present paper we study in detail the formation of the Josephson oscillations along the array.