Quantum Bits with Josephson Junctions

Abstract

Already in the first edition of this book [1], 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. At the time of writing, the most recent and comprehensive reviews of this field, which has grown rapidly in the past two decades, are Refs. [2,3]. We also recommend the reviews in Refs. [4][5][6][7][8][9][10][11][12] for additional perspectives on the field. 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. What is a qubit?As the name suggests, the field of QIP is concerned with information in quantum rather than classical systems. In a classical computer, the most basic unit of information is a bit, which can take two values: 0 and 1. In a quantum computer, the laws of quantum physics allow phenomena like superposition and entanglement. When discussing information processing in a quantum world, the most basic unit is therefore a quantum bit, usually called qubit, a two-level quantum system with a ground state |0 and an excited state |1 . Unlike a classical bit, which only has two possible

Engineering high-coherence superconducting qubits

“…[16][17][18][19] The design space for superconducting qubits is thus very rich, with many possible circuit variants. 20,21 The basic oscillatory circuit described above can be integrated with additional reactive elements to modify its characteristic impedance and associated coupling to the environment. 19 Furthermore, the area of the JJs, as well as the size and dimensionality of the passive microwave frequency elements embedding them, can be adjusted to trade between free-space radiation loss and surface loss.…”

Circuit centric quantum architecture design

“…Here, the information is stored in quantum degrees of freedom of nanofabricated and harmonic oscillators constructed from superconducting circuit elements. The superconducting qubits [3][4][5][6][7] are macroscopic in size and lithographically defined when compared with other technologies where information is stored in microscopic quantum systems. Among several other advantages of the superconducting qubits, the most significant advantage is the ease of production of such qubits.…”

Perfect state transfer on hypercubes and its implementation using superconducting qubits

“…Especially in large-scale quantum information processing (QIP), this is an important task, connecting two sites that may belong to the same or different quantum processors. The latter is nontrivial for many QIP realizations, such as solid state quantum computing and superconducting quantum computing [2][3][4][5][6][7][8]. It is also very important to find the systems that support this quantum information exchange between distant sites to realize this phenomenon.…”