Experimental evaluation of the current‐phase relation of a Josephson junction

Abstract

PurposeJosephson junctions act as active elements in superconducting electronics. The behavior of this nonlinear element is characterized by the relation between current and the quantum mechanical phase‐difference. For an accurate device modeling, detailed knowledge about this relation is necessary. This paper aims to discuss these issues.Design/methodology/approachTo obtain detailed information, a method for DC measurement of the current‐phase relation suitable for all kinds of superconducting circuit elements was accomplished.FindingsThe authors developed a linear transformation algorithm to calculate the current‐phase relation from the measured data.Research limitations/implicationsIt turns out that in future designs additional connections and special test structures are required to gain more knowledge about inductance values required for the algorithm.Originality/valueBased on the inverse calculation of that algorithm, the authors found a 7 percent deviation of the current‐phase relation of a standard superconductor/insulator/superconductor Josephson junction from the predicted sine‐wave behavior. Furthermore, the paper suggests to use this method to evaluate the current‐phase relation of new Josephson elements such as a superconductor/ferromagnet/superconductor junction. Therefore, the authors will deposit the new element directly on the chip with the test setup fabricated with standard Nb‐technology.