Superconducting quantum electronics

Abstract

Superconducting quantum electronics is formally born in 1911, three years after Heike Kamerlingh Onnes was able to liquefy helium at the University of Leiden in the Netherlands. Josephson junctions are simple devices made of two superconductors coupled through a thin barrier, which can be made of one of several layers of insulating, normal metal, or ferromagnetic material. This chapter discusses the surface impedance of superconductors and their behavior in the radiofrequency (RF) regime. After the Josephson junction discovery, many new applications surfaced and the Josephson junction has become to date the most versatile active element used for superconducting analogue, digital and quantum electronics. These applications include magnetometers and gradiometers based on RF and DC superconducting quantum interference devices (SQUIDs), Josephson voltage standards, analogue-to-digital converters, quasi-one-junction SQUIDs, digital logic circuits, quantum computing, quantum communication and quantum sensing. The chapter discusses some of its applications.