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.
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.
This chapter explores the foundational concepts underlying superconducting qubits, pivotal in modern quantum computing. It begins with the harmonic oscillator, fundamental to both classical and quantum mechanics. Section 2.1 introduces its classical and quantum descriptions, emphasizing energy quantization and assessing its potential as a qubit. Section 2.2 focuses on the quantum LC oscillator, integral to superconducting circuit theory. Starting with the classical dynamics of an LC circuit, we derive its Hamiltonian and transition to its quantum description using ladder operators. This section bridges classical circuit theory and quantum systems, paving the way to understanding superconducting qubits. Sections 2.3–2.5 examine key qubit types. Section 2.3 introduces phase, charge, and flux qubits, highlighting their operational principles and the physical parameters they encode, such as magnetic flux or electric charge. Section 2.4 delves into the transmon qubit, exploring its Hamiltonians and methods for control and measurement. Finally, Section 2.5 surveys recent advancements in superconducting qubit designs, offering insights into the evolution toward next-generation qubits. This chapter provides a comprehensive framework for understanding superconducting qubits, linking classical systems to quantum technologies, and contextualizing their role in advancing quantum computation.
This chapter provides a self-contained introduction to the basic aspects of Quantum Mechanics, focusing on what is must for Quantum Field Theory. The notions of state space, unitary operators, self-adjoint operators, and projective representation are covered as well as Heisenberg’s uncertainty principle. A complete proof of Stone’s theorem is given, but the spectral theory is covered only at the heuristic level. We provide an introduction to Dirac’s formalism, which is almost universally used in physics literature. The time-evolution is described in both the Schrödinger and the Heisenberg picture. A complete treatment of the harmonic oscillator, providing an introduction to the fundamental idea of creation and annihilation operators concludes the chapter.
The first objective of this chapter is to briefly review some of the basic ideas about the structure of matter, in particular the concepts of microscopic physics, in order to recall the knowledge gained in previous physics (and chemistry) courses and make it more precise. Our review will be very concise, and most statements will be made without any proof or detailed discussion. A second objective is to give a brief description of some of the crucial stages in the early development of quantum physics. We shall not follow the strict historical order of this development or present the arguments used at the beginning of the last century by the founding fathers of quantum mechanics; rather, we shall stress the concepts which we shall find useful later on. Our last objective is to give an elementary introduction to some of the basic ideas, like those of a quantum particle or energy level, that will reappear throughout this text. We shall base our review on the Bohr theory, which provides a simple, though far from convincing, explanation of how energy levels are quantized and how the spectrum of the hydrogen atom arises. This chapter should be reread later on, once the basic ideas of quantum mechanics have been made explicit and illustrated by examples. From the practical point of view, it is possible to skip the general considerations of Sections 1.1 and 1.2 at the first reading and begin with Section 1.3, returning to those two sections later on as needed.
Abstract This chapter reviews all the rules of quantum mechanics and their mathematical notation. It also considers quantum entanglement, a fundamental resource in quantum information. There are four basic postulates of quantum mechanics, that indicate how to represent physical systems, how to represent observations, how to carry out measurements, and how systems evolve when “not measured”. Before describing the laws of quantum mechanics, their mathematical background is first described, along with a Mach Zehnder interferometer experiment in which the (strange) readings on the detectors can be explained by quantum mechanics. This chapter also discusses the Dirac notation, qubits, Hilbert spaces, projective measurements and operations, unitary operations, eigenvectors and eigenvalues, spectral decomposition, applications of the spectral theorem, Dirac notation shorthands, and mixed states.
Quantum physics, also known as quantum mechanics, is one of the most profound and successful theories in modern science, fundamentally transforming our understanding of the microscopic world. It governs the behavior of matter and energy at atomic and subatomic scales, where classical physics fails to provide accurate explanations. This review paper presents a comprehensive examination of the fundamental concepts of quantum physics, including wave–particle duality, quantum states, superposition, uncertainty principle, quantum measurement, entanglement, and quantum dynamics. The paper traces the historical development of quantum theory, reviews seminal contributions from key physicists, and analyzes major theoretical frameworks such as Schrödinger’s wave mechanics, Heisenberg’s matrix mechanics, and Dirac’s formalism. A systematic literature review of 25 scholarly sources is conducted to highlight the evolution, interpretations, and applications of quantum concepts. A comparative analysis of classical and quantum physics is provided to emphasize conceptual differences and paradigm shifts. The discussion explores philosophical implications, experimental validations, and emerging applications in quantum computing, cryptography, and quantum technologies. Finally, the paper concludes by summarizing key insights and outlining future directions for research and education in quantum physics.
As noted in Chapter 8 of this book, electronic states of nanostructures are determined by quantum mechanics. Quantum mechanics is a fundamental theory in physics that describes the underlying theory concerning the world around us, from atoms, electrons, and molecules to materials, lasers, and other functioning circuits. The consequences of the quantization of energy states and their interaction with electromagnetic radiation and matter, and on the effects of quantum mechanics on the behavior of electrons lead to the field of quantum electronics . In this chapter, the following topics are explained: (a) an overview of the physics governing quantum mechanics; (b) the fundamental quantum electronics principles leading to the development of lasers, masers, and reversible quantum gates and circuits; (c) basic quantum gates developed based on quantum cells; (d) fabrication methods including self-assembly—as occurs for quantum dots (e.g. quantum -dot cellular automata ) and tunneling—as occurs for superconducting circuit techniques (e.g. Josephson tunnel junction); and (e) the protocols required to ensure uninfected information transmit through quantum communication channel and quantum error-correction techniques to clean up erroneous pairs and/or errors (or decoherence) in the quantum channel.