The study of light through the centuries has produced a number of theories and experiments. Newton advanced the corpuscular theory, building on the early Greek view of matter composed of atoms. Then Young essentially proved the wave nature of light through the interference experiments. Maxwell provided the firm theoretical basis for the wave nature. During the late 1800s and early 1900s, further experiments showed predictions based on a continuous wave led to the well-known ultraviolet catastrophe. Plank and Einstein originated and developed the notion of the photon as an elementary quantum of propagating electromagnetic (EM) energy. The first half of the 20th century saw the development of the field quantization and the quantum electrodynamics (QED). Feynmann labeled QED as ‘‘the best theory we have’’ to describe the matter-light interaction. The second half of the 20th century witnessed the development of the coherent and squeezed optical states attributable to Glauber and Yuen. The study of light and electromagnetic fields has a long history. This chapter explores the nature of light in terms of quantum optics.
The study of light through the centuries has produced a number of theories and experiments. Newton advanced the corpuscular theory, building on the early Greek view of matter composed of atoms. Then Young essentially proved the wave nature of light through the interference experiments. Maxwell provided the firm theoretical basis for the wave nature. During the late 1800s and early 1900s, further experiments showed predictions based on a continuous wave led to the well-known ultraviolet catastrophe. Plank and Einstein originated and developed the notion of the photon as an elementary quantum of propagating electromagnetic (EM) energy. The first half of the 20th century saw the development of the field quantization and the quantum electrodynamics (QED). Feynmann labeled QED as ‘‘the best theory we have’’ to describe the matter-light interaction. The second half of the 20th century witnessed the development of the coherent and squeezed optical states attributable to Glauber and Yuen. The study of light and electromagnetic fields has a long history. This chapter explores the nature of light in terms of quantum optics.
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.
In the mid-18th century, Isaac Newton regarded light as some extremely small particles. Based on this, Newton established the particle theory of light. In the mid-19th century, Huygens and Augustine Jean Fresnel conducted extensive research on light and concluded that light is a wave. Afterwards, Maxwell proposed the theory of electromagnetism. Maxwell believed that light is a wave with a wavelength within a limited range. With the establishment of Maxwell's equation electromagnetic wave theory, the wave nature of light began to dominate the mainstream consciousness; However, in the late 19th century, a series of experimental phenomena represented by the photoelectric effect could not be accurately explained by the wave theory of light. In 1905, Einstein proposed the concept of light quanta and successfully explained the photoelectric effect. While perfectly explaining these issues, a new question arises: what is the essence of light, given that both particle and wave properties can accurately reflect certain properties of light? It has always been the most fiercely debated issue in the history of optics. Einstein said that we are not yet clear about what light quanta are, and wave particle duality cannot fully explain optical phenomena. Based on the study of Albert Einstein's concept of quanta light, wave particle duality of light, string theory, and optical frequency combs, the author proposes the concept of lightstring, attempting to propose new ideas for studying the essence of light and its generation mechanism. Siwen Bi has been researching quantum remote sensing since March 2000 and quantum spectral imaging since June 2003, but has encountered some difficulties and problems. What is the basic theory of passive imaging in quantum remote sensing? How is technology implemented? What is the fundamental theory of quantum spectroscopy? The Implementation Technology of Quantum Optical Field Entangled States in Long Distance Quantum Detection Process? These difficulties and questions prompt the author of this article to contemplate and study the essence of light? What is the fundamental theory of the future technology of quantum optics? Siwen Bi conducted exploratory research on the nature of light in 2006. This article first provides an overview of the development history and research status of optics and describes the difficulties and shortcomings in fully explaining optical phenomena due to the wave particle duality of light quantum and light; Then, two inspiring viewpoints on optical frequency comb and chord theory were introduced. On this basis, the basic concept of optical string (optical frequency string), the prototype description of optical string, the mechanism of optical string generation, and the discussion of Lightstring, generation process are proposed and emphasized; Proposed the mechanism of string light effect. Published On Two Heuristic Viewpoints Concerning the Study of Light (October 13-15, 2014), New Viewpoints In Light Quantum Research: Lightstring (2016), Discuss wave-particle duality of light, (February 28, 2017), and an Exploratory research on the light quantum future technical basis (February 1, 2019). Over the past 17 years, achieved some original and innovative research results. some original innovative research achievements have been achieved. Received high praise from international scholars and professors, such as the American Journal of Physics and Applications, which sent me a congratulatory letter saying, "Dear Bi Siwen, Warmest greeting from the Editorial Department! It is reported that at the International conference on photo and optical Engineering (ICPOE 2014), a paper entitled" Two Enlightening Views on Optical Research "was published, and the theme of the paper impressed us deeply. It has attracted the attention of Photon researchers and Scholars ...Your research is highly appreciated by us … " And invite Professor Bi Siwen as a paper reviewer for the American Journal of Physics and Applications. I have received the paper review certificate, dated May 25th, 2018. Based on the above research, Siwen Bi elaborated on the geometric and kinematic characteristics of Lightstring, and proposed the essence of light based on the concept of Lightstring, in order to concretize the concept of light quanta. On this basis, the mechanism of string light effect based on the concept of optical string is proposed. An attempt has been made to further study the quantum and wave particle duality of light, gain a profound understanding of the nature of light, and answer the question "What is light?" by proposing a new approach and method for studying the nature of light and its generation mechanism. Proposed a study on optical quantum; The wave particle duality of light; New ideas, methods, and perspectives on the mechanism of light generation.
This chapter begins with a brief outline of some of the key motivations for considering a quantum theory: the early attempts to determine the spectral distribution of energy density of black bodies; stability of atoms and molecules; specific heats of solids; interference and diffraction of light beams; polarization of photons. The experimental foundations of wave mechanics are then presented in detail, but in a logical order quite different from its historical development: photo-emission of electrons by metallic surfaces, X- and γ-ray scattering from gases, liquids and solids, interference experiments, atomic spectra and the Bohr hypotheses, the experiment of Franck and Hertz, the Bragg experiment, diffraction of electrons by a crystal of nickel (Davisson and Germer), and measurements of position and velocity of an electron. The need for a quantum theory In the second half of the nineteenth century it seemed that the laws of classical mechanics, developed by the genius of Newton, Lagrange, Hamilton, Jacobi and Poincaré, the Maxwell theory of electromagnetic phenomena and the laws of classical statistical mechanics could account for all known physical phenomena. Still, it became gradually clear, after several decades of experimental and theoretical work, that one has to formulate a new kind of mechanics, which reduces to classical mechanics in a suitable limit, and makes it possible to obtain a consistent description of phenomena that cannot be understood within the classical framework. It is now appropriate to present a brief outline of this new class of phenomena, the systematic investigation of which is the object of the following sections and of chapters 4 and 14.
Classically, light is an electromagnetic phenomenon, described by Maxwell's equations. However, under certain conditions, such as low intensity or in the presence of certain nonlinear optical materials, light starts to behave differently, and we have to construct a ‘quantum theory of light’. We can exploit this quantum behaviour of light for quantum information processing, which is the subject of this book. In this chapter, we develop the quantum theory of the free electromagnetic quantum field. This means that we do not yet consider the interaction between light and matter; we postpone that to Chapter 7. We start from first principles, using the canonical quantization procedure in the Coulomb gauge: we derive the field equations of motion from the classical Lagrangian density for the vector potential, and promote the field and its canonical momentum to operators and impose the canonical commutation relations. This will lead to the well-known creation and annihilation operators, and ultimately to the concept of the photon. After quantization of the free electromagnetic field we consider transformations of the mode functions of the field. We will demonstrate the intimate relation between these linear mode transformations and the effect of beam splitters, phase shifters, and polarization rotations, and show how they naturally give rise to the concept of squeezing. Finally, we introduce coherent and squeezed states.
Have you ever tried to define light? If so, your definition is probably related to vision, the ability to see things. The Merriam-Webster English dictionary defines light as “something that makes vision possible”. However, the definition of the “nature of light” is a complex term already discussed by philosophers of Ancient Greece. In the 17th century, the debate on the matter focused on whether light was a particle or a wave, based on the different properties of light that had been gradually discovered over time. Isaac Newton (1642−1727) was a defender of the corpuscular theory of light, which considered light to be formed by particles, i.e., small pieces of matter, like dust or grains of sand. He was the author of Opticks (1706), the front cover of which appears in Fig. 1.1. Christian Huygens (1629–1695), on the other hand, supported the theory that light is a wave. These are two completely different definitions of the same physical concept. A range of experiments were developed to attempt to clarify this dilemma, but it was only until 1900 when Max Planck (1858-1947) introduced the basis of a theory that would go on to revolutionize scientific thinking, marking the beginning of modern physics: quantum theory. Developed during the 20th century thanks to advances made by scientists such as Niels Bohr, Born, Heisenberg, Schrödinger, Pauli, Dirac, Einstein or de Broglie, quantum theory clarified that light is neither a particle nor a wave, but that it has a dual nature: it behaves like a wave as it spreads but like a particle in its interactions with matter. In this book, we will specify where necessary whether light behaves as a particle or as a wave, although in most cases we refer to rays of light, which always represent the direction of propagation of light.
Modern attempts to understand light go back to Newton who considered light to be particles, the so called corpuscular theory, and the other school of Huygens, Young and others. Huygens and Young viewpoint emphasised the wave property. This difference of opinions persisted for close to two centuries till Maxwell theory solidly established light as a wave phenomenon associated with Electromagnetism. A serious schism so to speak was introduced into the theory of light with the understanding of "Light gas", the so called Black Body radiation. Einstein's photon hypothesis and Bose's successful derivation of the Planck spectrum put the corpuscular theory back in place, while classical description continues to be used as well. One may then wonder if this being a classical limit may have to be corrected when dealing with quantum phenomena. To most people's surprise, the classical description was in fact a subset of the full quantum description, and the classical states of light could be shown to be subsumed within the fully quantum description without having to take the limit of Planck's constant h going to zero. This was the resolution provided by E. C. G. Sudarshan's Diagonal representation as the most general formalism for dealing with light.