Quantum electrodynamics in modern optics and photonics: tutorial (original) (raw)
Related papers
1 A QED-Based Wave Theory of Light, Electrons, and their Quantized Interactions
2015
Quantum Electrodynamics (QED) is not a theory of physical causation but only a probabilistic prediction model that has been modified as needed to correspond to observations. Contrary to popular belief, QED does not model light as flying photons, but instead as wave-like probability amplitudes spreading in all directions from the source—by shrinks and turns. Where the amplitudes superpose constructively is where light-detection events are more probable. QED’s model supports the theory presented here: that light is a wave and electrons are wave-structures that absorb and emit light waves in discrete wave-packets (e-quants). E-quants are emitted directionally and then begin to spread in space and superpose with ambient radiation as do all free waves. An e-quant absorption is produced by the complex superpositioning, upon an electron, of all source and background waves. The e-quant detected is rarely, if ever, the e-quant emitted. This wave theory of light and electrons encompasses the ...
Quantum Optical Mechanics (QOM): Abolishing 'Light'. [UET6]
This paper replaces the hypothetical 'object' called 'Light' (wave/photon). This sixth report on a new research programme that is investigating the electromagnetic (EM) interaction. This paper analyzes the effects of interactions arising from multiple, remote electrons on one or several, local 'target' electrons. These interactions are the result of the new quantized form of the EM impulse introduced in the previous paper. This model is used to re-interpret various optical effects that have previously required the existence of a fundamental object known as 'LIGHT': a basic entity, considered to be either a particle or a wave (or even both?-the 'photon') that travels across space. In contrast, this new EM model is constructed upon the key role of the 'light' emission processes, categorized as either oscillatory (as in antenna) or transitory (as within atoms). These real emission processes are now integrated into the asynchronous action-at-a-distance model of the EM interaction that is the basis of this new theory. Mathematically, this new model describes algebraically how variable or periodic phenomena (that have been assumed require the use of waves) can be explained by periodic, asynchronous, remote interactions between point particles without any use of differential equations (including the wave equation). This paper now extends the earlier pair-wise interaction between two electrons into the many-body world of macroscopic reality. The two key ideas of interaction saturation and selection are now introduced, which totally differentiate this theory from all other theories constructed around universal, continuous interaction (or 'force') models. By eliminating all the ray, wave and photon models of 'light' this paper now extends the original Newtonian mechanical philosophy of nature to the major domain of optics: both classical and quantum. The emphasis is on the electrons and on the relationship between electrons and not on some hypothetical 'carrier' that travels between them – this is the Newtonian action-at-a-distance particulate model extended to multiple times. The idea of selection leads to the introduction of information waves that identify the location and velocities of all other electrons that might participate in a ray-like exchange of momentum between pairs of electrons (saturation) that always act like particles (real trajectories across space). These supra-luminal waves do not carry momentum but ensure that the interaction minimizes the exchange of action across a non-local region of space. This new model resolves the long-time paradox of electrons as waves or particles: electrons are seen here as real point particles that interact periodically (rather than continuously) together; the focus is on the relationship between them that can be described by the discrete mathematics of particles or the periodic mathematics usually associated with waves. This paper includes the first analytical solution to the 3D scattering of two electrons – in the center-of-mass frame of reference both electrons are shown to go in quantized spiraling, conical motions: towards each other and then away from each other. The present theory provides an alternative to Feynman's mathematical approach to " the mysterious properties of light " while providing a physical explanation for some of the calculational diagrams introduced by Feynman in his approach to quantum electrodynamics (QED). This now replaces all field theories of 'light' without introducing the concept of the photon or virtual particles and so eliminates all QED infinities in the physical properties associated with the interactions of electrons arising from the false idea of vacuum polarization, returning the vacuum to its Newtonian role as the passive, empty space between real particles. This new EM theory establishes a firm foundation for a new quantum theory that covers all scales of nature from the macroscopic to the heart of the atomic nucleus, while covering the complete range of interaction sets from a pair of electrons to the myriads of electrons existing in macroscopic objects. The next (companion) paper will explain the wave-like properties of electrons while providing a new, comprehensive theory of quantum measurement. This next paper will finally establish the critical link between the realistic model of the micro-world introduced so far and the macroscopic world of scientific measurements.
Classical electrodynamics and the quantum nature of light
Journal of Physics A: Mathematical and General, 1997
A review of old inconsistencies of Classical Electrodynamics (CED) and of some new ideas that solve them is presented. Problems with causality violating solutions of the wave equation and of the electron equation of motion, and problems with the non-integrable singularity of its self-field energy tensor are well known. The correct interpretation of the two (advanced and retarded) Lienard-Wiechert solutions are in terms of creation and annihilation of particles in classical physics. They are both retarded solutions. Previous work on the short distance limit of CED of a spinless point electron are based on a faulty assumption which causes the well known inconsistencies of the theory: a diverging self-energy (the non-integrable singularity of its self-field energy tensor) and a causalityviolating third order equation of motion (the Lorentz-Dirac equation). The correct assumption fixes these problems without any change in the Maxwell's equations and let exposed, in the zero-distance limit, the discrete nature of light: the flux of energy from a point charge is discrete in time. CED cannot have a true equation of motion but only an effective one, as a consequence of the intrinsic meaning of the Faraday-Maxwell concept of field that does not correspond to the classical description of photon exchange, but only to the smearing of its effects in the space around the charge. This, in varied degrees, is transferred to QED and to other field theories that are based on the same concept of fields as space-smeared interactions.
The Photon Ontology of first quantized Electrodynamics
During the past couple of decades, there has been a remarkable technical development of quantum optics and photonics, but unfortunately this has not yet allowed to get closer to answering the fundamental question "What is a photon?", which was frequently discussed by Einstein. In principle, though, it is feasible to bridge the gap between the successful theories of classical and quantum electrodynamics in terms of a first quantized theory based on the Riemann-Silberstein formulation of the Maxwell equations, in which the Hamilton operator of the photon depends linearly on the momentum operators, similarly to the Dirac Hamiltonian. This circumstance per se, however, does not appear to generate any better understanding of the ontology of a single photon. It is proposed to go one step further and subject the first quantized photon theory to the requirement of being confined to a bounded space region in the framework of a physical account which is related philosophically to the Wheeler-Feynman absorber theory of electrodynamics and to Mach's principle. In the mathematical setting of the so-called Qbox, formalized in terms of the unit cube in three-dimensional space, the requirement of commuting, self-adjoint momentum operators leads to defining a novel wave function quantization in terms of a broad family of boundary isometries, which has a physically privileged geometrical sub-family of quasi-periodic translational isometries (QPTI). The key significance of the QPTI boundary parameters and their associated eigenfunctions is to epitomize the spatial "collapse" phenomenon of the wave function and, concomitantly, to elucidate the physical sense of the Huygens principle of electrodynamics for the case of a single photon. This ontic as well as epistemic wave function approach to describing a light quantum incorporates an experimentally validated boundary ontology and an epistemic description in the Qbox bulk, replacing the standard wave-particle duality by the notion of two-wave duality.
QED: The Strange Theory of Light and Matter
Leonardo, 1991
The Strange Theory of Light and Matter By Richard P. Feynman Celebrated for his brilliantly quirky insights into the physical world, Nobel laureate Richard Feynman also possessed an extraordinary talent for explaining difficult concepts to the general public. Here Feynman provides a classic and definitive introduction to QED (namely, quantum electrodynamics), that part of quantum field theory describing the interactions of light with charged particles. Using everyday language, spatial concepts, visualizations, and his renowned "Feynman diagrams" instead of advanced mathematics, Feynman clearly and humorously communicates both the substance and spirit of QED to the layperson. A. Zee's introduction places Feynman's book and his seminal contribution to QED in historical context and further highlights Feynman's uniquely appealing and illuminating style.
Advances in Physics
We present the theoretical foundations and the implementation details of a density-functional approach for coupled photons, electrons, and effective nuclei in non-relativistic quantum electrodynamics. Starting point of the formalism is a generalization of the Pauli-Fierz field theory for which we establish a one-to-one correspondence between external fields and internal variables. Based on this correspondence, we introduce a Kohn-Sham construction which provides a computationally feasible approach for ab-initio light-matter interactions. In the mean-field limit for the effective nuclei the formalism reduces to coupled Ehrenfest-Maxwell-Pauli-Kohn-Sham equations. We present an implementation of the approach in the real-space real-time code Octopus. For the implementation we use the Riemann-Silberstein formulation of classical electrodynamics and rewrite Maxwell's equations in Schrödinger form. This allows us to use existing time-evolution algorithms developed for quantum-mechanical systems also for Maxwell's equations. We introduce a predictorcorrector scheme and show how to couple the Riemann-Silberstein time-evolution of the electromagnetic fields self-consistently to the time-evolution of the electrons and nuclei. Furthermore, the Riemann-Silberstein approach allows to seamlessly combine macroscopic dielectric media with a microscopic coupling to matter currents. For an efficient absorption of outgoing electromagnetic waves, we present a perfectly matched layer for the Riemann-Silberstein vector. We introduce the concept of electromagnetic detectors, which allow to measure outgoing radiation in the far field and provide a direct way to record various spectroscopies. We present a multi-scale approach in space and time which allows to deal with the different length-scales of light and matter for a multitude of applications. We apply the approach to laser-induced plasmon excitation in a nanoplasmonic dimer system. We find that the self-consistent coupling of light and matter leads to significant local field effects which can not be captured with the conventional light-matter forward coupling. For our nanoplasmonic example we show that the self-consistent foward-backward coupling leads to changes in observables which are larger than the difference between local density and gradient corrected approximations for the exchange correlation functional. In addition, in our example we observe harmonic generation which appears only beyond the dipole approximation and can be directly observed in the outgoing electromagnetic waves on the simulation grid. The self-consistent coupling of the electromagnetic fields to the ion motion reveals significant energy transfer from the electromagnetic fields to matter on the scale of a few tens of femtoseconds. Overall, our approach is ideally suited for applications in nano-optics, nano-plasmonics, (photo) electrocatalysis, light-matter coupling in 2D materials, cases where laser pulses carry orbital angular momentum, or light-tailored chemical reactions in optical cavities to name but a few.
Cornell University - arXiv, 2022
This is a write-up of a short tutorial talk on high-intensity QED, videopresented at the 2021 annual Christmas meeting of the Central Laser Facility at Rutherford-Appleton Lab, UK. The first half consists of a largely historical introduction to (quantum) electrodynamics focussing on a few key concepts. This well-established theory is then compared to its strong-field generalisation when a high-intensity laser is present. Some supplementary material and a fair amount of references have been added.
Quantum electrodynamics of qubits
Physical Review A, 2007
Systematic description of a spin one-half system endowed with magnetic moment or any other two-level system (qubit) interacting with the quantized electromagnetic field is developed. This description exploits a close analogy between a two-level system and the Dirac electron that comes to light when the two-level system is described within the formalism of second quantization in terms of fermionic creation and annihilation operators. The analogy enables one to introduce all the powerful tools of relativistic QED (albeit in a greatly simplified form). The Feynman diagrams and the propagators turn out to be very useful. In particular, the QED concept of the vacuum polarization finds its close counterpart in the photon scattering off a two level-system leading via the linear response theory to the general formulas for the atomic polarizability and the dynamic single spin susceptibility. To illustrate the usefulness of these methods, we calculate the polarizability and susceptibility up to the fourth order of perturbation theory. These ab initio calculations resolve some ambiguities concerning the sign prescription and the optical damping that arise in the phenomenological treatment. We also show that the methods used to study two-level systems (qubits) can be extended to many-level systems (qudits). As an example, we describe the interaction with the quantized electromagnetic field of an atom with four relevant states: one S state and three degenerate P states.