Abstract Quantum optics is the subject that deals with optical phenomena that can only be explained by treating light as a stream of photons rather than as electromagnetic waves. In principle, the subject is as old as quantum theory itself, but in practice, it is a relatively new one, and has really only come to the fore during the last quarter of the twentieth century.
Abstract Quantum optics is the subject that deals with optical phenomena that can only be explained by treating light as a stream of photons rather than as electromagnetic waves. In principle, the subject is as old as quantum theory itself, but in practice, it is a relatively new one, and has really only come to the fore during the last quarter of the twentieth century.
The behavior of light and its interaction with matter is certainly one of the most interesting phenomena of physics. It has puzzled thinkers and scientists in ancient Greece (Archimedes) and through the Middle Ages, at least since the times of Robert Grosseteste (1168–1235), right up to the theories of Galileo Galilei and Isaac Newton. The classical electromagnetic theory of light (see Tab. 13.1) was beautifully established in the second half of the nineteenth century with the Maxwell equations. Quantum optics is nothing other than the quantum theory of light. It finds its roots in Planck's discovery (1900) that the assumption of energy quantization for a harmonic oscillator allowed us to solve the black-body problem (see Subsec. 1.5.1). The successive early steps that led to the quantization of the electromagnetic field include Einstein's explanation of the photoelectric effect with the introduction of the quantum of light (see Subsec. 1.2.1) and the interpretation of atomic spectra (see Subsec. 1.5.4). Quantum optics is usually not covered by conventional textbooks on quantum mechanics. We include its discussion here for two main reasons: first, because it is a fundamental and advanced application of the basic framework of quantum mechanics, and, second, because in the last 30 years quantum optics has played (and is still playing) a major role in the advancement and understanding of quantum mechanics.
Authored by a highly regarded international researcher and pioneer in the field, An Introduction to Quantum Optics: Photon and Biphoton Physics is a straightforward overview of basic principles and experimental evidence for the quantum theory of light. This book introduces and analyzes some of the most exciting experimental research to date in the field of quantum optics and quantum information, helping readers understand the revolutionary changes occurring in optical science. Paints a picture of light in terms of general quantum interference, to reflect the physical truth behind all optical observations Unlike most traditional books on the subject, this one introduces fundamental classical and quantum concepts and measurement techniques naturally and gradually as it explores the process of analyzing typical experimental observations. Separating itself from other books with this uncommon focus on the experimental part of analysis, this volume: Provides a general overview of the optical coherence of light without quantization Introduces concepts and tools of field quantization and quantum optics based on the principles and rules of quantum mechanics Analyzes similarities and differences between classical and quantum coherence Concentrates on key research topics in quantum optics Explains photon and biphoton physics by examining the devices and experimental procedures used to test theories This book is basic enough for students, but it also covers a broad range of higher-level concepts that will benefit scientists and other professionals seeking to enhance their understanding of practical and theoretical aspects and new experimental methods of measurement. This material summarizes exciting developments and observations and then helps readers of all levels apply presented concepts and tools to summarize, analyze, and resolve quantum optical problems in their own work. It is a great aid to improve methods of discovering new physics and better understand and apply nontraditional concepts and interpretations in both new and historical experimental discoveries.
Quantum optics is a research field with somewhat elastic boundaries. In its narrowest definition, the field is restricted to the study of those optical phenomena that can only be understood in terms of the quantum theory of light. Even this narrow scope includes a rich diversity of effects, and there have been particularly striking recent advances in the use of optical experiments to demonstrate aspects of fundamental quantum mechanical theory, such as vacuum fluctuations, the Bose-Einstein statistics, superposition states in particle interference, and violations of Bell's inequality.
In this introductory chapter we focus on the interaction of optical fields with matter because it forms the basis of signal amplification in all optical amplifiers. According to our present understanding, optical fields are made of photons with properties precisely described by the laws of quantum field theory [1]. One consequence of this wave–particle duality is that optical fields can be described, in certain cases, as electromagnetic waves using Maxwell's equations and, in other cases, as a stream of massless particles (photons) such that each photon contains an energy h ν, where h is the Planck constant and ν, is the frequency of the optical field. In the case of monochromatic light, it is easy to relate the number of photons contained in an electromagnetic field to its associated energy density. However, this becomes difficult for optical fields that have broad spectral features, unless full statistical features of the signal are known [2]. Fortunately, in most cases that we deal with, such a detailed knowledge of photon statistics is not necessary or even required [3, 4]. Both the linear and the nonlinear optical studies carried out during the last century have shown us convincingly that a theoretical understanding of experimental observations can be gained just by using wave features of the optical fields if they are intense enough to contain more than a few photons [5]. It is this semiclassical approach that we adopt in this book. In cases where such a description is not adequate, one could supplement the wave picture with a quantum description.
Quantum optics is the branch of physics that investigates the interaction of light with matter at the quantum level, where the discrete nature of photons and quantum states of atoms, molecules, and solid-state systems become dominant. Quantum optics systems provide the experimental and theoretical foundation for understanding nonclassical states of light, quantum coherence, entanglement, and measurement at the quantum limit. Over the past few decades, advances in laser technology, nonlinear optics, and precision measurement have transformed quantum optics from a fundamental discipline into a key enabler of quantum technologies, including quantum communication, quantum computing, quantum sensing, and quantum metrology. This review presents a comprehensive overview of the physical principles, system architectures, and experimental platforms of quantum optics. Emphasis is placed on light sources, atom–photon interaction systems, detection techniques, and emerging applications, along with current challenges and future research directions.
Light occupies a special position in our attempts to understand nature both classically and quantum mechanically. We recall that Newton, who made so many fundamental contributions to optics, championed a particle description of light and was not favorably disposed to the wave picture of light. However, the beautiful unification of electricity and magnetism achieved by Maxwell clearly showed that light was properly understood as the wave-like undulations of electric and magnetic fields propagating through space. The central role of light in marking the frontiers of physics continues on into the twentieth century with the ultraviolet catastrophe associated with black-body radiation on the one hand and the photoelectric effect on the other. Indeed, it was here that the era of quantum mechanics was initiated with Planck's introduction of the quantum of action that was necessary to explain the black-body radiation spectrum. The extension of these ideas led Einstein to explain the photoelectric effect, and to introduce the photon concept. It was, however, left to Dirac to combine the wave-and particlelike aspects of light so that the radiation field is capable of explaining all interference phenomena and yet shows the excitation of a specific atom located along a wave front absorbing one photon of energy. In this chapter, following Dirac, we associate each mode of the radiation field with a quantized simple harmonic oscillator, this is the essence of the quantum theory of radiation.