Light is a quantum electrodynamic entity and hence bundles of rays must be describable in this framework. We demonstrate the duality in the description of elementary optical phenomena in terms of two-point correlation functions and in terms of collections of light rays. The generalizations necessary to deal with two-slit interference and diffraction by a rectangular slit are worked out and the usefulness of the notion of rays of darkness is illustrated. Quantum electrodynamics, to which Julian Schwinger has so definitively contributed1), is the theory of light at the present state of our knowledge. It has provided models of other field theories, particularly of weak interactions. Despite this the quantum electrodynamic description of light has not been satisfactorily developed. One recalls that Max Planck, the pioneer of quantum theory made a systematic study of light rays and radiative transfer 2) in which quantum concepts did not enter in any significant way. The general theory of quantum optics has so far ignored the question of the connection between light rays and quantum electrodynamics with the notable exception of the recent work of Wolf3). Unlike the notion of light rays in the short wavelength
Light is a quantum electrodynamic entity and hence bundles of rays must be describable in this framework. We demonstrate the duality in the description of elementary optical phenomena in terms of two-point correlation functions and in terms of collections of light rays. The generalizations necessary to deal with two-slit interference and diffraction by a rectangular slit are worked out and the usefulness of the notion of rays of darkness is illustrated. Quantum electrodynamics, to which Julian Schwinger has so definitively contributed1), is the theory of light at the present state of our knowledge. It has provided models of other field theories, particularly of weak interactions. Despite this the quantum electrodynamic description of light has not been satisfactorily developed. One recalls that Max Planck, the pioneer of quantum theory made a systematic study of light rays and radiative transfer 2) in which quantum concepts did not enter in any significant way. The general theory of quantum optics has so far ignored the question of the connection between light rays and quantum electrodynamics with the notable exception of the recent work of Wolf3). Unlike the notion of light rays in the short wavelength
There are two opposing points of view on the nature of light: the first one manifests the wave-particle duality as a fundamental property of the nature; the second one claims that photons do not exist and the light is a continuous classical wave, while the so-called “quantum” properties of this field appear only as a result of its interaction with matter. In this paper we show that many quantum phenomena which are traditionally described by quantum electrodynamics can be described if light is considered within the limits of classical electrodynamics without quantization of radiation. These phenomena include the double-slit experiment, the photoelectric effect, the Compton effect, the Hanbury Brown and Twiss effect, the so-called multiphoton ionisation of atoms, etc. We show that this point of view allows also explaining the “wave-particle duality” of light in Wiener experiments with standing waves. We show that the Born rule for light can easily be derived from Fermi’s golden rule as an approximation for low-intense light or for short exposure time. We show that the Heisenberg uncertainty principle for “photons” has a simple classical sense and cannot be considered as a fundamental limitation of accuracy of simultaneous measurements of position and momentum or time and energy. We conclude that the concept of a “photon” is superfluous in explanation of light-matter interactions.
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.
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 fundamental fact for quantum physics which has emerged from experimental investigations in the field is a double duality of wave and particle concepts. The wave theory of light, firmly grounded by the wave explanations of interference and diffraction and by Maxwell’s electromagnetic theory of light waves, is now recognized as giving but one aspect of the nature of radiation. The corpusclar aspect of radiation is revealed in the photoelectric effect and in the Compton effect. In these effects Planck’s constant appears as a universal constant which connects the wave and particle modes of description of the same radiation.
This paper reviews humanity's understanding of photons, the evolution of quantum mechanics and quantum electrodynamics (QED), and analyzes their physical interpretations and philosophical implications. It attempts to uncover the true nature of photons by exploring possible hidden variables in the double-slit experiment. The wave-particle duality of photons, as posited by quantum mechanics, appears to me to lack verisimilitude. By designing a thought experiment involving a photon double-slit setup, I seek to falsify the notion that photons generate coherence, or so-called wave-function superposition, within the light field between the slits and the screen. This endeavour aims to demonstrate the pure particle nature of photons. This paper further explores the intrinsic relationship between electromagnetic waves and photons by examining the wavelength of electromagnetic radiation. It posits that electromagnetic waves are fundamentally pure particle-waves. An analysis of QED elucidates the potential influence of photon momentum on photon interactions, an effect that could have profound implications for quantum information transmission. This paper explores the non-wave-particle duality of photons through the double-slit experiment and the double-slit observer experiment. The essence of photons is purely particle-like. The thought experiment of the photon double-slit experiment is pivotal in demonstrating that photons and other particles—such as electrons, atoms, and macromolecules—are purely particulate in nature. Moreover, in space, photons can interfere with each other's paths based on their momentum. This can simultaneously alter the trajectory of photons and even modify their velocity. That is to say, a photon beam possessing greater momentum may carry along a portion of photon beams with lesser momentum, propagating them over considerable distances. The wavelength of a light wave fundamentally represents the distance between consecutive photons as they queue and advance through space. A longer wavelength corresponds to a greater distance between photons, causing them to diverge more widely in space, as seen with radio waves. Conversely, a shorter wavelength implies closer proximity between photons, resulting in denser emission and a highly directional nature, as seen in gamma rays. Photons within the visible spectrum may occasionally transmit information bearing specific content. This information, conveyed via photons, can propagate over distances ranging from several metres to thousands of kilometres.
Today, the nature of light is accounted for by one of the jewels of physics, quantum electrodynamics (QED), the fundamental theory of light and matter. Yet owing to its infinite complexity, scientists still debate how its central concept, the photon, can be reconciled with the perceived existence of light waves, emerging 200 years ago in the wake of Young's double slit diffraction experiment. Ever since, the phenomenon of diffraction has been viewed to embody the wave nature of light, leading to the schizophrenic wave-particle duality. The latter does not exist in QED which is photon based without the existence of waves. Here we introduce the new paradigm that diffraction images directly reflect the fundamental quantum states of light. This is revealed by analysis of the evolution of modern versions of Young's experiment performed with differently modified laser light and photon-based detection. In conventional quantum mechanics, corresponding to first order QED, the fundamental photon nature of light remains hidden since different quantum states produce only two basic types of diffraction patterns that may also be explained by coherent and incoherent wave superposition. The true photon based substructure of light is shown to clearly emerge through characteristic diffraction images in second order QED. The degeneracy of the first order images is lifted, the wave-particle equivalence breaks down, and the patterns directly reveal the true quantum substructure of light. This allows the replacement of the conventional concept of wave coherence by a precise order-dependent degree of coherence that quantifies the interference and diffraction behavior of all quantum states of light.