It has been observed that every photon is, in a sense, virtual - being emitted and then sooner or later absorbed. As the motif of a quantum radiation state, the photon shares these characteristics of any virtual state: that it is not directly observable; and that it can signify only one of a number of indeterminable intermediates, between matter states that are directly measurable. Nonetheless, other traits of real and virtual behavior are usually quite clearly differentiable. How 'real', then, is the photon? To address this and related questions it is helpful to look in detail at the quantum description of light emission and absorption. A straightforward analysis of the dynamic electric field, based on quantum electro-dynamics, reveals not only the entanglement of energy transfer mechanisms usually regarded as 'radiative' and 'radiationless'; it also gives significant physical insights into several other electromagnetic topics. These include: the propagating and non-propagating character in electromagnetic fields; near-zone and wave-zone effects; transverse and longitudinal character; the effects of retardation, manifestations of quantum uncertainty and issues of photon spin. As a result it is possible to gain a clearer perspective on when, or whether, the terms 'real' and 'virtual' are helpful descriptors of the photon.
It has been observed that every photon is, in a sense, virtual - being emitted and then sooner or later absorbed. As the motif of a quantum radiation state, the photon shares these characteristics of any virtual state: that it is not directly observable; and that it can signify only one of a number of indeterminable intermediates, between matter states that are directly measurable. Nonetheless, other traits of real and virtual behavior are usually quite clearly differentiable. How 'real', then, is the photon? To address this and related questions it is helpful to look in detail at the quantum description of light emission and absorption. A straightforward analysis of the dynamic electric field, based on quantum electro-dynamics, reveals not only the entanglement of energy transfer mechanisms usually regarded as 'radiative' and 'radiationless'; it also gives significant physical insights into several other electromagnetic topics. These include: the propagating and non-propagating character in electromagnetic fields; near-zone and wave-zone effects; transverse and longitudinal character; the effects of retardation, manifestations of quantum uncertainty and issues of photon spin. As a result it is possible to gain a clearer perspective on when, or whether, the terms 'real' and 'virtual' are helpful descriptors of the photon.
In this chapter, we examine some of the principal attributes of electromagnetic radiation that feature in photons. At the outset, it is worth asserting that the photon concept owes its legitimacy to the quantum theory of light. As we shall see in later chapters, the photon is formally regarded as a quantum of excitation of any specific optical mode. In the literature, one can find occasional mentions of photons qualified by an adjective, such as dipole photons, electric photons, ballistic photons, etc.,* These should be regarded as potentially misleading because each alludes to a property that is more correctly associated with a particular kind of phenomenon. Even if the distinction between "real" and "virtual" photons represents one of the most widely used descriptors, it does not signify a clear-cut difference. We thus begin by listing the following photon properties, all of which can be involved in specific forms of optical interaction, with the exception of the first.
A richly diverse range of phenomena and applications, frequently in the context of laser applications, owe their means of operation to the properties of the photon. Yet, since the arrival of the laser, the distinctive and often paradoxical nature of the photon has become more than ever evident, and what the optics community now understands by a ‘photon’ has become richer – certainly less simple, than Einstein’s original conception. There has been a marked expansion in the pace of development since the now familiar derivative term ‘photonics’ first emerged, and in much current theory any dividing line between ‘real’ and ‘virtual’ photons proves to be illusory. So if, in this technical sense, no photon can ever be regarded as entirely real, one is drawn to deeper questions of whether the photon is ‘real’ in the broader sense of reality. Some would argue that electromagnetic fields are closer to irreducible reality. Yet whether we elect to describe optical phenomena in terms of fields or photons, neither represents what is actually measured. The surest ground has to be found where theory is cast in terms that explain or predict actual observations, under given conditions. It is consistent with the path integral formulation of quantum mechanics that derivations should not prescribe what intervenes between setup and measurement, but instead allow for all possibilities. Indeed, one of the beauties of the associated mathematics is its capacity to home in on possibilities that most closely conform to post-event physical interpretation. Still, we can ask: how much do or can we know about the photon itself? How much information could this entity contain or convey? And, how essential is a photonic formulation of theory? This study focuses on some of the key issues.
Photons and electrons One of the great technical achievements of the second half of the 20th century was the invention of the laser. With its help extremely intense light could be produced. Furthermore, it even became posssible to excite a single resonator mode so that both the frequency and the propagation direction of the emitted radiation field are extraordinarily sharp. The mere existence of such high-intensity single-mode fields – the real problem that was ingeniously solved was to generate them – is no matter of surprise. We know from classical electromagnetic theory that the amplitude of a monochromatic electromagnetic field can take on arbitrarily large values. This is a direct consequence of the linearity of Maxwell's equations. What does this mean for quantized radiation fields? Certainly, the mentioned property of classical fields must also be retained in the quantum mechanical description. Since the electromagnetic energy is quantized in ‘packets’ of magnitude h ν (photons), the number of photons in a given mode must be unlimited, in principle. All this is very well known. However, it becomes noteworthy when we compare the behaviour of photons with that of electrons. Amazingly, it turns out that an electronic quantum state can be occupied by one electron, at maximum. (Strictly speaking, in the description of the electronic state the spin variable must be included.) This drastic difference in the collective behaviour of photons and electrons could, in fact, not be expected from what we know from single photons and electrons. Both of them have particle-like as well as wave-like properties. However, when many of them are present, they exhibit quite different a demeanour.
Aims/ objectives: The consideration of the three tasks, formulated below, is the aim of the given work. The first task of the paper presented is to analyse the existing viewpoints and to give the conclusion on the real photon status. To represent the clear and understandable explanation of the nature of the corpuscular-wave dualism and to give an insight into physics of the photon absorption process is the second task of the given review. The third task of the paper presented - to give the experimental proof for the Dirac theoretical conclusion, that the transitions of the quantum system from an equilibrium state to an excited state are not instantaneous and that a part of the time, related to a duration of the stay between the states can be determined. Study design: The theory of quantum Fermi liquid, the developed Dirac quantisation method, the theory of quantum Rabi oscillations and experimental results of the stationary electron spin resonance (ESR) spectroscopy were used. Place and Duration of Study: Heat-Mass Transfer Institute of National Academy of Sciences of RB, Belarusian State University and M.V.Lomonosov Moscow State University, between January 2014 and July 2014. Methodology: We have used the quantum 1D Fermi liquid model for the description of 1D correlated electronic systems, elaborated in the application to the quantised electromagnetic (EM) field, the Jaynes-Cummings model (JCM) of quantum Rabi oscillations, new Slepyan-Yerchak- Hoffmann-Bass model of propagating quantum Rabi oscillations and new fully quantum space-time quantisation method. Results: The status of the photon in the modern physics is analysed. In the physics of elementary particles the photon is considered to be the genuine elementary particle. The development of the viewpoint of the experts in the quantum electrodynamics theory is considered. It was established its change from the opinion, that the description of the photon to be the particle is impossible to the viewpoint on the photon to be the particle, that is, coinciding with the viewpoint, represented in the Standard Model of the physics of elementary particles. The quantized Maxwellian EM-field represents itself, according to the new conceptual model reviewed, the sets of 1D rays, the own structure of each ray is discrete - 1D-lattice of spin-1 bosons. Therefore, the structure of EM-field in boson model resembles the structure of the carbon frame of organic polymers like to trans-polyacetylene in the matter. Photons in the given concept are the corpuscles, propagating along EM-field boson-”atomic” chains. In other words, EM-field boson- ”atomic” chains represents themselves the medium for the photons’ propagation. In the structural aspect photons in usual conditions are chargeless spin 1/2 topological relativistic solitons of Su- Schrieffer-Heeger family. Spinless charged solitons of the same family can also be formed in socalled ”doped” EM-field structure. The origin of waves in the EM-field boson-”atomic” structure is determined by the mechanism, being to be quite analogous to the formation of Bloch waves in the solid state of condensed matter. The expression for the corresponding wave function representing itself the set of Bloch-like waves is given. Just, the given function allows to describe correctly the wave properties of the light, including the interference. Corpuscular properties of EM-field including those ones by its interaction with matter are described by independent scalar field function obtained from the solution of Schr¨odinger equation [nonstationary in general case] and usually called wave function. The term ”wave” seems to be incorrect in application to the given function and has to be corrected in all literature on quantum theory, including textbooks. The physics of quantum absorption process is analysed. It is argued, in accordance with Dirac guess, that the photon revival takes place by its absorption. It is concluded, that after the energy and impulse transfer to the absorbing system the photon state is a pinned state, in which it possesses the only by spin. The reviewed rather unusual spectroscopic electron spin resonance absorption characteristics of carbon nanotubes and superconducting ceramics, obtained with the participation of the authors and of the other research groups and being earlier unexplained, were correctly interpreted within the frames of the phenomenological model of the spectroscopic transition dynamics with finite time of the transfer of absorbing systems in an excited state. Moreover, it was established, that the time of the transfer of absorbing systems in an excited state governs the characteristics of the stationary ESR signal registered in the carbon nanotubes and superconducting ceramics. Conclusion: To describe correctly the EM-field properties including corpuscular-wave dualism [which is explained in a natural way] it is necessary to use the full variant of Schr¨ odinger’s theory, taking into consideration two scalar functions. The result, that the time of the transfer of absorbing systems into an excited state governs the characteristics of the stationary ESR signal is significant for the stationary spectroscopy at all, since the transfer of absorbing systems in an excited state is considered in the stationary spectroscopy at present to be instantaneous.
During these three years we focused on several topics in quantum otpics and quantum electrodynamics. A central theme in our investigations is that of the photon wave function. Can quantum optics and quantum electrodynamics experiments be described simply, in position space, with the help of a wave function describing the photon(s) featured in the experiment ? The answer to that question is not quite obvious: the usual description of photons takes place in the reciprocal space of wave vectors. But these experiments call for a wave mechanical description in the position representation, as is done in quantum mechanics textbooks in situations featuring massive particles. Moreover, in a recent experiment [1], single photon trajectories through a Young two-slit setup have been observed. In order to try and describe these trajectories formally, it is natural to build a wave mechanical formalism for photons. We therefore studied in detail the formal construction of the photon wave function, an object which was little studied until the 1990s. We also studied the properties of the photon wave function in the presence of sources.To do that, we considered several open (interacting) quantum systems. We saw that there exists in principle an infinite number of possibilities when defining the photon wave function. We emphasised several criteria on the basis of which it appears that only three choices for the wave function are interesting. One of them coincides with an object introduced and used by Glauber [2] to study light detection andthe correlations of the electromagnetic field in the quantum regime. We also saw that, in the absence of sources, the propagation equation for a single photon is formally equivalent to Maxwell’s equations. At low photon numbers, the wave function formalism can be very useful. We adapted it to interacting systems,first, to cavity quantum electrodynamics (QED) [3], in particular to the experiments carried out by Serge Haroche’s group [4]. We proposed a simple model to describe photons in QED cavities. With this model, and with the helpof the photon wave function, we studied the propagation of photons escaping a cavity. We also constructed the Lindblad master equation without introducing nonunitary quantum jumps (also see [5]). We finally investigated the spacetime evolution of a photon which is emitted during the decay of an atomic electron. After having carefully studied the dynamics of the electronic decay, especially at very short times [6, 7], we set out to describe the emitted electromagnetic field as rigorously as possible. This emitted field, surprisingly, does not evolve causally. Though this is not entirely unexpected in view of Hegerfeldt’s theorem, which states [8] that causality is impossible for quantum systems which are described by a Hamiltonian with a spectrum which is bounded by below, we identified [9] two other sources of non causality. One of them was predicted qualitatively by Shirokov [10], while the other one, which is completely new as far as we can tell, is still to be better understood
A conceptual model is developed for the processes of photon emission and absorption. While the emission of light is well known in terms of quantum changes in energy levels of an electron, the fundamental physical processes are incompletely understood. How exactly does the photon emerge from the electron? How is light absorbed by matter? These foundational conceptual questions are the focus of this paper. We show that it is possible to develop new insights into this problem, based on the cordus model, which is a non-local hidden-variable solution. We start by predicting the structures of the photon and electron, both the internal geometric substructures, and their discrete fields. The model predicts that there are different mechanisms for the fields of the photon and electron, and uses this to explain the characteristics of the evanescent and electric fields. We then show how the bonding constraints arise on the electron, and how these require the electron to emit its excess energy. The process whereby a photon is created and separated out of the electron is identified. Photon emission and absorption thus result from an interaction between the discrete field elements and the internal structures. Emission is thus an escapement mechanism whereby matter particules that are overprescribed in position can get rid of that energy.