Recent demonstrations of macroscopic quantum coherence in Josephson junction based electronic circuits have opened an entirely new dimension for research and applications in the established field of Josephson electronics. In this article we discuss basic Josephson circuits for qubit applications, methods of quantum description of these circuits, and circuit solutions for qubit couplings. Principles of manipulation and readout of superconducting qubits are reviewed and illustrated with recent experiments using various qubit types.
Already in the first edition of this book (Barone and Paterno,"Fundamentals and Physics and Applications of the Josephson Effect", Wiley 1982), a great number of interesting and important applications for Josephson junctions were discussed. In the decades that have passed since then, several new applications have emerged. This chapter treats one such new class of applications: quantum optics and quantum information processing (QIP) based on superconducting circuits with Josephson junctions. In this chapter, we aim to explain the basics of superconducting quantum circuits with Josephson junctions and demonstrate how these systems open up new prospects, both for QIP and for the study of quantum optics and atomic physics.
The reasons for the failure to develop a successful Josephson tunnel junction made from high-temperature superconducting cuprates is discussed. The difficulties in developing a theoretical analysis of even simple-to-make cuprate Josephson devices are pointed out. The development of alternative Josephson devices based on the fabrication of engineered microbridges is addressed, and an overview is given of successful YBCO microbridges. Emphasis is given to focused ion beam and step-edge microbridges.