This appendix provide a self-contained presentation of the open systems and quantum optics methods used in other parts of the book (e.g., studying the relaxation of a microwave cavity or a qubit, the driving of a quantum amplifier, etc.). Half of the appendix is devoted to the derivation of master equations for small systems that are in contact with Markovian environments. The other half of the appendix is devoted to the development of an alternative input–output description of how those systems absorb information from the environment and reflect it back.

In this chapter, we discuss the notion of a quantum simulator as a device that emulates a complex quantum many-body Hamiltonian, and a quantum annealer as an extension of such a paradigm that focuses on the preparation of the ground state in those Hamiltonians. Starting from the Landau–Zener processes and the adiabatic theorem, we illustrate how such ground states can be prepared by slow (adiabatic) deformations of a Hamiltonian. We discuss how this results in an adiabatic quantum computing algorithm and how, depending on the Hamiltonian we apply it to, we can solve problems of different classical and quantum complexity. The chapter closes with a thorough discussion of the D-Wave quantum annealer as a real-world superconducting quantum simulator of Ising-type models. This discussion centers both on the design of the superconducting annealers as well as on the conclusion from the literature on how this device works in practice, including how quantum operations are still possible even in the pressence of decoherence. We close the chapter with an outlook on the challenges that need to be overcome for making coherent quantum annealers and universal adiabatic quantum computers.

We discuss the building blocks of a universal quantum computer within the circuit model of computation and how this is implemented using superconducting quantum circuits. In particular, we discuss, one by one, the creation of quantum registers, resetting of quantum bits, qubit measurements, single-qubit operations, and universal two-qubit gates, and how these are all implemented using the tools from earlier chapters. We discuss how to calibrate the errors in the qubits and in the operations, assigning them complete descriptions via positive maps. We explain how these errors can be corrected and how to implement a fault-tolerant quantum computer, focusing on the paradigm of stabilizer codes and the surface code in particular. We close with a discussion on the outlook for quantum computers in the near term and the NISQ paradigm of computation.

In this chapter, we develop the conditions to observe quantum fluctuations and quantum phenomena (entanglement, superpositions, etc.) in quantum circuits. Assuming the right conditions of temperature, we develop the quantum mechanical theory that models those fluctuations in a circuit built from nondissipative superconducting elements. We use this theory of circuit quantization to obtain the quantum Hamiltonians for microwave resonators and waveguides, for superconducting qubits of various types, and for other elements such as SQUIDs. The chapter closes with an illustration of how the same theory provides us with numerical methods to study the eigenstates, eigenenergies, and dynamics of said Hamiltonians.

In this chapter, we review the basic properties of superconductors, illustrating that they go beyond describing a metal without resistance. We develop London's mesoscopic theory of superconductivity as a quantum mechanical description of the charged superfluid, which accounts for the behavior of the superconductor under electromagnetic fields. Using this theory, we explain the flux quantization for supercurrents flowing in closed loops and derive the energetics of the Josephson junction from the tunneling of Cooper pairs.

This chapter is the introduction to this book, its motivation and its design and how it can be applied to the design of undergraduate and graduate courses on quantum optics and superconducting quantum circuits.

In this chapter, we review basic concepts from quantum mechanics that will be required for the study of superconducting quantum circuits. We review the fundamental idea of energy quantization and how this can be formalized, using Dirac's ideas, to develop a quantum mechanical description that is consistent with the classical theory for a comparable object. We review the notions of quantum state, observable and projective and generalized measurements, particularizing some of these ideas to the simple case of a two-dimensional object or qubit.