Electrodynamic Approach Research Articles

Combined computational quantum chemistry and classical electrodynamics approach for surface enhanced infrared absorption spectroscopy.

Surface enhanced spectroscopy, which enhances the signal intensity of molecules on a surface, facilitates the study of molecular properties, even down to a single-molecule level if a scanning probe is used. To realize the full potential of surface enhanced spectroscopy, a clear theoretical understanding is indispensable. However, quantum chemical calculations for surface enhanced spectroscopy are not simple because of the violation of the widely used dipole approximation. The spatial structure of electric near-field in the close proximity of a surface strongly depends on the geometry of the metal nanostructure as well as on the incident wavelength. Therefore, in principle, a universal model for electric near-field cannot exist. To address this issue, we have developed a generalized light-matter interaction model from first-principles quantum chemical calculations by using the multipolar Hamiltonian, in which the spatial structure of the electric field is fully considered. Here, we incorporate computational electrodynamics for surface enhanced infrared (IR) absorption spectroscopy in the model, where electric near-field around a Ag ellipsoid is obtained and used for IR calculations. Furthermore, we have devised a method to successfully reproduce the peak selectivity observed experimentally.

Collectively induced exceptional points of quantum emitters coupled to nanoparticle surface plasmons

Exceptional points, resulting from non-Hermitian degeneracies, have the potential to enhance the capabilities of quantum sensing. Thus, finding exceptional points in different quantum systems is vital for developing such future sensing devices. Taking advantage of the enhanced light-matter interactions in a confined volume on a metal nanoparticle surface, here we theoretically demonstrate the existence of exceptional points in a system consisting of quantum emitters coupled to a metal nanoparticle of subwavelength scale. By using an analytical quantum electrodynamics approach, exceptional points are manifested as a result of a strong-coupling effect and observable in a drastic splitting of originally coalescent eigenenergies. Furthermore, we show that exceptional points can also occur when a number of quantum emitters are collectively coupled to the dipole mode of localized surface plasmons. Such a quantum collective effect not only relaxes the strong-coupling requirement for an individual emitter, but also results in a more stable generation of the exceptional points. Furthermore, we point out that the exceptional points can be explicitly revealed in the power spectra. A generalized signal-to-noise ratio, accounting for both the frequency splitting in the power spectrum and the system's dissipation, shows clearly that a collection of quantum emitters coupled to a nanoparticle provides a better performance of detecting exceptional points, compared to that of a single quantum emitter.

Nonrelativistic quantum electrodynamic approach to polarizabilities of light atoms

We derive polarizabilities for light atoms and their relativistic and radiative corrections by using nonrelativistic quantum electrodynamics (NRQED). We find out that if we use NRQED directly on the polarizabilities, it will lead to gauge-dependent terms which should be cancelled out by summing all the Feynman diagrams. The elimination of these gauge-dependent terms will become very cumbersome in the calculations of relativistic and radiative corrections. By combining the Power–Zienau–Woolley transformation with NRQED, we have simplified this process. In addition to this, the combination allows us to obtain not only the electric dipole polarizability but also other kinds of polarizabilities, such as magnetic, Coulomb-transversal and hyperpolarizabilities, in a unified way. In the following article we introduce this combined method and show a systematic procedure to derive the polarizabilities as well as the relativistic, radiative corrections to some of them.

Quantum repeater protocol using an arrangement of QED–optomechanical hybrid systems

In this paper we consider the quantum repeater protocol for distributing the entanglement to two distant three-level atoms. In this protocol, we insert six atoms between two target atoms such that the eight considered atoms are labeled by 1; 2;... 8, while only each two adjacent atoms (i; i + 1) with i = 1; 3; 5; 7 are entangled. Initially, the separable atomic pair states (1,4) and (5,8) become entangled by performing interaction between atoms (2,3) and (6,7) in two optomechanical cavities, respectively. Then, via performing appropriate interaction between atoms (4,5) in an optical cavity quantum electrodynamics (QED) approach, the target atoms (1,8) are finally become entangled. Throughout this investigation, the effects of mechanical frequency and optomechanical coupling strength to the field modes on the produced entanglement and the related success probability are evaluated. It is shown that, the time period of produced entanglement can be developed by increasing the mechanical frequency. Also, maximum of success probability of atoms (1,8) is increased by decreasing the optomechanical coupling strength to the field modes in most cases.

Localised plasmons in sphere-like fullerenes and nanoparticles with conducting shells: Classical electrodynamic approach

Based on the classical electrodynamic approach, we consider localised plasmons in fullerenes and small particles with metal layers and shells. At low energies of the radiation quantum, models of fullerenes as conducting shells are used taking into account the contribution of only π electrons, and at high energies, of both π and σ electrons. The obtained maxima of the scattering cross sections correspond to the values of 20 and 27 eV that were determined experimentally and in quantum models for the maxima of the photoionisation cross sections of fullerenes C60 and C28, respectively. Approximate analytical results are presented for resonant frequencies, Q factors, radiation patterns, scattering and absorption cross sections for sphere-like particles and fullerenes, as well as integral equations and functionals for dielectric particles with a conducting shell of arbitrary shape. Analysis relies on the use of effective surface conductivity.

Quantum dynamics of a molecular emitter strongly coupled with surface plasmon polaritons: A macroscopic quantum electrodynamics approach.

We study a molecular emitter above a silver surface in the framework of macroscopic quantum electrodynamics and explore the population dynamics including non-Markovian effects. The theory we present is general for molecular fluorescence in the presence of dielectrics with any space-dependent, frequency-dependent, or complex dielectric functions. Furthermore, the proposed theory allows us to calculate the memory kernel of polaritons using computational electrodynamics packages. In the limit of a high vibration frequency, the different strengths of exciton-polariton couplings lead to distinct characteristics in the population dynamics, e.g., Franck-Condon-Rabi oscillation. (The frequency of Rabi oscillation is dependent on the Franck-Condon factor.) Additionally, in a specific condition, we derive a parameter-free formula that can be used to estimate the exciton-polariton coupling between a molecular emitter and a nanocavity, and the coupling estimated by our theory is in good agreement with the reported experimental results [Chikkaraddy et al., Nature 535, 127-130 (2016)].

G factor of the [(1s)2(2s)22p]2P3/2 state of middle‐Z boronlike ions

Theoretical g‐factor calculations for the first excited 2P3/2 state of boronlike ions in the range Z=10–20 are presented and compared with the previously published values. The first‐order interelectronic‐interaction contribution is evaluated within the rigorous quantum electrodynamics (QED) approach in the effective screening potential. The second‐order contribution is considered within the Breit approximation. The QED and nuclear recoil corrections are also taken into account.

Electrodynamic improvements to the theory of magnetostatic modes in ferrimagnetic spheres and their applications to saturation magnetization measurements

Electrodynamic theory applied to the analysis of TEn0p mode resonances in ferromagnetic spheres placed either in metallic cavities or in the free space is compared with Walker-Fletcher's theory of so-called magnetostatic modes. The influence of the diameter of the sample, its permittivity and the permittivity of the surrounding media on the resonance frequencies of a few modes is analyzed. It is shown that the dominant resonances are essentially related either to negative values of the diagonal component of the permeability tensor or, for clockwise circularly polarized magnetic fields, to negative effective permeability. The electrodynamic theory is used to determine the saturation magnetization (Ms) from measured TEn01 frequency differences. Measurements on different samples confirmed that Ms can be determined using an electrodynamic approach with uncertainties of the order of 2% regardless of sample sizes, metal enclosures or static magnetic field values.

Leveraging radiation reaction via laser-driven plasma fields

We investigated the effect of a plasma charge separation field on radiation reaction (RR) in laser–plasma interactions. By implementing the plasma field equation developed in one-dimension into the classical Landau–Lifshitz formula, our numerical test-particle modeling revealed distinctive plasma electron dynamics in three regimes: the low density underdense regime, the near-critical density (NCD) regime and the highly overdense one. It is discovered from the electron trajectories and gamma-ray emission that the RR effect is mostly significant at near-critical plasma densities. The underlying mechanism is well interpreted by the theoretical analysis from the perspective of the potential contained in the charge separation field and demonstrated in two dimensional particle-in-cell simulations using the quantum electro-dynamic photon emission approach. Our findings indicate that the NCD plasma is the most efficient medium to leverage RR and generate high-energy and low-divergence gamma-photons.

Superradiant and transport lifetimes of the cyclotron resonance in the topological insulator HgTe

We investigate the superradiance effects in three-dimensional topological insulator HgTe with conducting surface states. We demonstrate that the superradiance can be explained using the classical electrodynamic approach. Experiments using the continuous-wave spectroscopy allowed to separate the energy losses in the system into intrinsic and radiation losses, respectively. These results demonstrate that the superradiance effects are not sensitive to the details of the band structure of the material.

Electrodynamic Concentration of Non-ferrous Metallic Particles in the Moving Gas-powder Stream: Mathematical Modeling and Analysis

The paper presents theory, modeling, and analysis of a novel electrodynamic concentration approach for submillimeter-sized conductive metal particles focusing in moving gas-powder stream. Such method is of particular interest in blown-powder feeding fabrication industry (e.g., powder-fed additive manufacturing) to generate a tightly focused powder stream. Conceptual design of a concentration generator is proposed with two different configurations: The doublet Halbach permanent magnet quadrupoles (doublet-Halbach-PMQs) and the doublet electromagnet quadrupoles (doublet-EMQs). Analytical models for magnetic forces and concentration angles were built. Numerical calculations were conducted for pure aluminum particles with a radius of <math xmlns='http://www.w3.org/1998/Math/MathML'> <mrow> <mn>50</mn><mo><</mo><msub> <mi>R</mi> <mi>p</mi> </msub> <mo>≤</mo><mn>500</mn><mtext> </mtext><mi>μ</mi><mi>m</mi></mrow> </math>. It was found that the magnetic force and the concentration angle increase with an increase of the particle size. The numerical results indicate that the proposed concentration generator with doublet-Halbach-PMQs configuration cannot be effectively used for small-size particle concentration. By contrast, the concentration generator with doublet-EMQs configuration under high frequency is capable to concentrate particles with a radius of <math xmlns='http://www.w3.org/1998/Math/MathML'> <mrow> <msub> <mi>R</mi> <mi>p</mi> </msub> <mo>></mo><mn>150</mn><mtext> </mtext><mi>μ</mi><mi>m</mi></mrow> </math>. The particles with a radius of <math xmlns='http://www.w3.org/1998/Math/MathML'> <mrow> <msub> <mi>R</mi>

Transient Electromagnetic-Thermal Simulation of Dispersive Media Using DGTD Method

In this paper, the transient electromagnetic–thermal simulation is performed for dispersive media using the discontinuous Galerkin time-domain (DGTD) method. Both the frequency-dependent and temperature-dependent properties of dispersive media are considered in the modeling. Instead of executing the complex convolution in the time domain, an auxiliary differential equation (ADE) method is employed to manipulate dispersive media, where the polarization current density is introduced as an auxiliary variable. While dealing with the thermal issue by the DGTD, the heat flux is utilized to construct the ADE for solving the thermal conduction equation. As the heat source in electromagnetic–thermal simulation, the transient power loss density for three typical dispersive media (Debye, Lorentz, and Drude) is derived by the electrodynamic approach and also explained with equivalent circuit models. The validity and accuracy of the proposed electromagnetic–thermal co-simulation method are demonstrated by the numerical examples.

The Super-Coherent State of Biological Water

Exceptional solvent, water is the life-giving molecule on Earth: it covers about 70% of the Earth’s surface, accounts for 65% of a human and 90% of macromolecules present in biological systems. If the water did not exist, no chemical reactions, no transport of nutrients and waste, etc. would exist. In a word, without water, there would be no life. Within the range of envi-ronmental temperature and pressure, water is found in three conventional physical aggregation states plus one: solid (ice), liquid (liquid water), gas-eous (water vapor) and semi-crystalline (biological water). Most of the models proposed to explain the peculiar properties of water start from the study of an isolated water molecule, then extend its characteristics and behaviors to the water molecules bound to it. Each model aims to predict the behavior of water in its three conventional aggregation states and subsequently verify its compatibility with experimental chemical-physical properties. Problems arise when, through intermolecular electrostatic at-traction forces (short-range forces), a lot of water molecules are assembled to form the liquid phase together. None of the water models proposed to date, based on short-range forces, is able to describe satisfactorily the “abnormal” chemical-physical behavior of water. In the present work, it is presented the Quantum Electro Dynamics (QED) approach to water, introduced and developed, with the contribution of other physicists and researchers, by Giuliano Preparata and Emilio del Giudice, two Italian theoretical physicists and researchers of the National Institute of Nuclear Physics (INFN), over the last thirty years.

METHOD OF STRIP LINES’ TE MODES CHARACTERISTICS CALCULATION

The paper is devoted to the calculation of the electromagnetic field in a stripline based transmission line for the TE-modes. TE-mode is one of the closest to the main mode, especially at the high frequencies, and should be considered in the multiple-mode resonators. Moreover, TE-mode is the main mode in the slotline at ane frequency. The method of solving the electromagnetic field problem of computing the characteristics of TE-modes of the slotlines is proposed. The proposed method is based on a rigorous electrodynamic approach and has no restrictions on the geometric and electrophysical parameters of the lines. The problem is reduced to the eigenvalues and eigenvectors problem, which is solved by the 2D finite element method applied to the cross-section of the line. The resulting solutions provide the possibility of obtaining the distribution of the component of the electromagnetic field and calculate the integral characteristics of the stripline, such as effective dielectric permittivity, which defines wavelength in the line, and characteristic impedance, which describes the relation between current and voltage in the equivalent transmission line. The distribution of the electric field components in the slotline is shown. The results of the effective dielectric permittivity and characteristic impedance calculation for the slotline with various geometrical and electrophysical parameters at different operating frequencies are presented. The obtained values of the effective parameters are in good agreement with other known calculated and measured results. The proposed method can be applied to any structures of strip lines in an arbitrary medium with any dielectric or metal objects placed near the line. Thus, such a method is suitable for the analysis and design of micro mechanically tunable devices as well.

Resonance Energy Transfer in Arbitrary Media: Beyond the Point Dipole Approximation

In this work, we present a comprehensive theoretical and computational study of donor/acceptor resonance energy transfer (RET) beyond the dipole approximation, in arbitrary inhomogeneous and dispersive media. The theoretical method extends Forster theory for RET between particles (molecules or nanoparticles) to the case where higher multipole transitions in the donor and/or acceptor play a significant role in the energy transfer process. In our new formulation, the energy transfer matrix element is determined by a fully quantum electrodynamic expression, but its evaluation requires only classical electrodynamics calculations. By means of a time domain electrodynamical approach (TED), the matrix element evaluation involves the electric and magnetic fields generated by the donor and evaluated at the position of the acceptor, including fields associated with transition electric dipoles, electric quadrupoles, and magnetic dipoles in the donor, and the acceptor response to the electric and magnetic fields and ...

A semi-analytical model for the study of the evolution of a microwave plasma channel

A simplified electrodynamic (non-electrostatic) approach is developed to study the evolution of a single microwave (MW) plasma channel (plasmoid) forming in the above breakdown electric field of linearly polarized MW beam (or beams). The results of numerical calculations in air within the pressure range P = 60 − 140 Torr based on this approach coupled with a sufficiently complete system of plasma chemical reactions, diffusion and photoionization are presented. Quasi-stationary values of the main MW plasmoid characteristics are estimated. The estimated values of the plasma density, the length of the plasmoid and its dipole moment agree well with the experimental results.

Receiving antenna electrodynamic model in terms of waveguide representation of HF field

The receiving antenna is an important part of a radio channel that requires electrodynamic approach in mathematical simulation of its characteristics. Since the invention of radio, and due to further theoretical studies of radio signal transmission, the following situation has arisen: researchers’ attention to receiving antennas is inversely proportional to the factor by which their number exceeds the number of transmitting antennas. We address the problem of building a receiving antenna electrodynamic model in terms of a waveguide representation of HF field. Structurally, the antenna is considered as metal wires of a finite length and arbitrary configuration. Current distribution in antenna is calculated using the long-line theory and normal-mode approach. The mathematical representation of the receiving antenna electrodynamic model is calculation expressions for receiving coefficients of normal modes. They reflect the effects of receiving antenna characteristics, including its directional pattern, on effectiveness of the incident HF field energy conversion into the energy of the driven current waves and final distribution of net current in antenna. These expressions are used to derive the expression to calculate the effective length of the receiving antenna.&#x0D; The obtained mathematical expressions of the receiving antenna electrodynamic model do not contradict the principle of antenna reciprocity.&#x0D; We present calculation formulas for the receiving coefficients and excitation of the isotropic antenna electromagnetic model.

Электродинамическая модель приемной антенны в рамках волноводного представления КВ-поля

The receiving antenna is an important part of a radio channel that requires electrodynamic approach in mathematical simulation of its characteristics. Since the invention of radio, and due to further theoretical studies of radio signal transmission, the following situation has arisen: researchers’ attention to receiving antennas is inversely proportional to the factor by which their number exceeds the number of transmitting antennas. We address the problem of building a receiving antenna electrodynamic model in terms of a waveguide representation of HF field. Structurally, the antenna is considered as metal wires of a finite length and arbi-trary configuration. Current distribution in antenna is calculated using the long-line theory and normal-mode approach. The mathematical representation of the receiving antenna electrodynamic model is calculation expressions for receiving coefficients of normal modes. They reflect the effects of receiving antenna characteristics, including its directional pattern, on ef-fectiveness of the incident HF field energy conversion into the energy of the driven current waves and final distribution of net current in antenna. These expressions are used to derive the expression to calculate the effective length of the receiving antenna.&#x0D; The obtained mathematical expressions of the re-ceiving antenna electrodynamic model do not contradict the principle of antenna reciprocity.&#x0D; We present calculation formulas for the receiving coefficients and excitation of the isotropic antenna electromagnetic model.

Radio Emission of the High-Latitude Ionosphere as a Result of the Cutoff Mode of the Auroral Ionospheric Duct

Issues of radio emission of the auroral ionosphere are considered with the use of the classical electrodynamics approach, according to which a natural waveguide is formed in the Earth’s ionosphere owing to formation of a trough in the high-latitude ionosphere. Parameters and characteristics of the auroral ionospheric dielectric duct have been estimated on the basis of the obtained experimental data on the properties of the ionospheric trough. The hypothesis that the LF and VLF electromagnetic auroral radio emission in the high-latitude ionosphere is due to the approach of the auroral waveguide to the cutoff mode has been considered. It has been found that the radio emission bands correspond to the eigenmodes of the ionospheric duct under consideration. It has been shown that, within the proposed approach, not only the radio emission frequency band of the high-latitude ionosphere but also the polarization of the radio emission observed in the experiments can be explained.

(Invited) A Quantum Electrodynamics Formulation of Energy Transfer Via Electric Dipole-Magnetic Dipole and Magnetic Dipole-Magnetic Dipole Interaction of Two Optically Active Ions

The nonradiative electron transfer process between optically active ions in luminescent materials via electric dipole (ED)-magnetic dipole (MD) and magnetic dipole-magnetic dipole interaction has been investigated using a molecular quantum electrodynamics (QED) approach. The QED approach provides an intuitively simple but rigorous method of calculating the energy transfer probability through multipolar interactions such as the ED-MD and MD-MD interactions considered in this work. More details of this approach and its application to resonant energy transfer between molecules through the ED-ED interaction can be obtained from Craig and Thirunamachandran [1] and references therein. The energy transfer process between two ions in the present study is shown schematically in Figure 1. While the energy levels have been considered to be discrete within the QED formulation for calculating the transition probabilities, the broadening of the energy levels in solids has been processed using the spectral line shape functions without using the special normalization in the energy space used by Dexter [2]. The transition probabilities have been simplified further using experimentally observable spectroscopic parameters such radiative lifetime and absorption cross section. The final expressions for transition probability includes additional periodic functions that are meaningful only in the short wavelength regime of the electromagnetic radiation. In this presentation, we will consider two classes of Feynman diagrams to calculate the transition rates for the energy transfer process through ED-MD and MD-MD interactions. In all the cases, the interaction between two ions is mediated by photons. In one class of diagrams, the photon is emitted first by ion A, and then absorbed by ion B at a later time. In other class of diagram, the photon is absorbed by ion B first and then emitted by ion A. The second class pertains to emission and absorption of a virtual photon. The theoretical details of calculating the transition probabilities and their significance will be presented. It will also be shown how this approach could be used in other luminescence processes to determine their plausibility and the transition rates. [1] D. P. Craig and T. Thirunamachandran, Molecular Quantum Electrodynamics, Dover Publications, Mineola, New York (1998). [2] D. L. Dexter, J. Chem. Phys. 21, 836 (1953). Figure 1. A schematic diagram of energy transfer from ion A to ion B. The associated eigenstates and eigenenergies for each of these ions are indicated. The wavy line indicates transfer of energy from the ion A and B while the solid arrows indicate the electronic transitions each ion is going through simultaneously. Figure 1