Electrodynamic Interactions Research Articles

Calculation of electrodynamic characteristics and electron-wave interaction in gyrotron resonators based on the ANGEL software package

Calculation of electrodynamic characteristics and electron-wave interaction in gyrotron resonators based on the ANGEL software package

Cavity confinement in defect-based honeycomb photonic crystals and the design of waveguide–cavity Fano-coupler for dielectric loss sensing

Honeycomb photonic crystal (PhCs) also known as photonic graphene exhibits salient features such as common complete photonic bandgap, topological states, and degrees of freedom to manipulate local density of states for efficient light–matter interactions. In this work, we report the cavity confinement offered by the six different point defect geometries of honeycomb PhCs. It is found that the reported point defect geometries are capable of supporting high confinement with low effective mode area of the order of 10−4 m2. To make use of this cavity confinement, a Fano-coupler is designed based on waveguide–cavity (WG-C) interactions in honeycomb PhC. The transmission/reflection profiles of a WG-C geometry shows typical Fano resonances with the quality factor of the order of 104. Comparing square and triangular PhCs, honeycomb WG-C shows a relatively stable Fano-lineshape resonance for a variation in imaginary part of the dielectric permittivity (ɛr′′) of an unknown dielectric material loaded at the center of the cavity from 0 to 0.01. The proposed WG-C Fano-coupler is suitable for dielectric loss sensing over a conventional cavity perturbation method, in which Fano resonance is sustained with Q factor variation of 25,805 to 2431 for ɛr′′ variation from 0 to 0.01, respectively. Due to the nature of PhC cavity decay dynamics, two different linear sensitive regimes with the dielectric loss sensitivity of 96.901/ɛr′′ (for ɛr′′=0 to 0.005) and 26.911/ɛr′′ (for ɛr′′=0.005 to 0.01) are observed. We anticipate that the cavity confinement and Fano-interactions reported in honeycomb PhCs might be useful not only to explore sensing elements but also for unraveling light–matter interactions in cavity quantum electrodynamics, quantum optics and lasing systems.

A holistic vibration analysis of an electric engine including mechanical and electrodynamic interactions

AbstractIn this paper, a method for vibration analysis of electric engines and associated structure is presented. For this purpose, a multi‐body simulation (MBS) is extended in such a way that electromagnetic loads can be considered using the finite element method (FEM). Subsequently, the determined loads lead to an excitation of the structural vibrations and a sound radiation of the engine, which is analyzed at selected operating points. A test rig will be used to validate the implemented method. Finally, different design variations of the engine are evaluated with respect to their acoustic behavior. The developed method is not limited to the presented application, but it can be applied to any system with electric drives.

First-Principles Simulation of Dielectric Function in Biomolecules.

The dielectric spectra of complex biomolecules reflect the molecular heterogeneity of the proteins and are particularly important for the calculations of electrostatic (Coulomb) and electrodynamic (van der Waals) interactions in protein physics. The dielectric response of the proteins can be decomposed into different components depending on the size, structure, composition, locality, and environment of the protein in general. We present a new robust simulation method anchored in rigorous ab initio quantum mechanical calculations of explicit atomistic models, without any indeterminate parameters to compute and gain insight into the dielectric spectra of small proteins under different conditions. We implement this methodology to a polypeptide RGD-4C (1FUV) in different environments, and the SD1 domain in the spike protein of SARS-COV-2. Two peaks at 5.2–5.7 eV and 14.4–15.2 eV in the dielectric absorption spectra are observed for 1FUV and SD1 in vacuum as well as in their solvated and salted models.

Coherent radio emission from a population of RS Canum Venaticorum systems

Coherent radio emission from stars can be used to constrain fundamental coronal plasma parameters, such as plasma density and magnetic field strength. It is also a probe of chromospheric and magnetospheric acceleration mechanisms. Close stellar binaries, such as RS Canum Venaticorum (RS CVn) systems, are particularly interesting as their heightened level of chromospheric activity and possible direct magnetic interaction make them a unique laboratory to study coronal and magnetospheric acceleration mechanisms. RS CVn binaries are known to be radio-bright but coherent radio emission has only conclusively been detected previously in one system. Here, we present a population of 14 coherent radio emitting RS CVn systems. We identified the population in the ongoing LOFAR Two Metre Sky Survey as circularly polarised sources at 144 MHz that are astrometrically associated with known RS CVn binaries. We show that the observed emission is powered by the electron cyclotron maser instability. We use numerical calculations of the maser’s beaming geometry to argue that the commonly invoked ‘loss-cone’ maser cannot generate the necessary brightness temperature in some of our detections and that a more efficient instability, such as the shell or horseshoe maser, must be invoked. Such maser configurations are known to operate in planetary magnetospheres. We also outline two acceleration mechanisms that could produce coherent radio emission, one where the acceleration occurs in the chromosphere and one where the acceleration is due to an electrodynamic interaction between the stars. We propose radio and optical monitoring observations that can differentiate between these two mechanisms.

Analytical and simulation modeling of linear antenna arrays on surface of a cylindrical shape

The main technical characteristics of the transmitting and receiving radio electronic equipment (operating frequency bands, zones and ranges of action, overall dimensions and weight of the equipment) largely depend on the characteristics of the antennas used in them. When placing antenna systems on aircraft, it is necessary to take into account the electrodynamic interaction of structural elements leading to distortions of the electromagnetic field. Simulation software can significantly improve the quality of the analysis of electromagnetic field distortions introduced by the antenna and carrier. Using the Electrodynamic Simulation Environment Computer Simulation Technology Microwave Studio, the directivity characteristics of linear vibrator antenna arrays located on a screen such as a perfectly conducting cylinder of finite dimensions are investigated. Analytical expressions are obtained for calculating the directional pattern and directional effect of an antenna array on an ideally conducting cylinder, the lateral surface of which can represent fragments of an aircraft in the ultrahigh frequency range, and an analysis of the regularities of the spatial-frequency selectivity of transmission (reception) of electromagnetic waves is carried out.

Transition between Random and Periodic Electron Currents on a DNA Chain.

By resorting to a model inspired to the standard Davydov and Holstein-Fröhlich models, in the present paper we study the motion of an electron along a chain of heavy particles modeling a sequence of nucleotides proper to a DNA fragment. Starting with a model Hamiltonian written in second quantization, we use the Time Dependent Variational Principle to work out the dynamical equations of the system. It can be found that, under the action of an external source of energy transferred to the electron, and according to the excitation site, the electron current can display either a broad frequency spectrum or a sharply peaked frequency spectrum. This sequence-dependent charge transfer phenomenology is suggestive of a potentially rich variety of electrodynamic interactions of DNA molecules under the action of electron excitation. This could imply the activation of interactions between DNA and transcription factors, or between DNA and external electromagnetic fields.

Data-driven reaction coordinate discovery in overdamped and non-conservative systems: application to optical matter structural isomerization

Optical matter (OM) systems consist of (nano-)particle constituents in solution that can self-organize into ordered arrays that are bound by electrodynamic interactions. They also manifest non-conservative forces, and the motions of the nano-particles are overdamped; i.e., they exhibit diffusive trajectories. We propose a data-driven approach based on principal components analysis (PCA) to determine the collective modes of non-conservative overdamped systems, such as OM structures, and harmonic linear discriminant analysis (HLDA) of time trajectories to estimate the reaction coordinate for structural transitions. We demonstrate the approach via electrodynamics-Langevin dynamics simulations of six electrodynamically-bound nanoparticles in an incident laser beam. The reaction coordinate we discover is in excellent accord with a rigorous committor analysis, and the identified mechanism for structural isomerization is in very good agreement with the experimental observations. The PCA-HLDA approach to data-driven discovery of reaction coordinates can aid in understanding and eventually controlling non-conservative and overdamped systems including optical and active matter systems.

A study of the global magnetic activity of the star Kepler-17 using light curve inversion with bipartite regularization

A new method of light curve inversion with bipartite regularization (LIBR), which is complementary to the previous treatments by Bonomo and Lanza and Estrela and Valio, is used to reconstruct the physical properties of star spots on the solar-type star Kepler-17 by using the full Q1- Q17 data set. The Markov Chain Monte Carlo (MCMC) method was applied to find the best profile of the reconstructed surface. The known value of the rotation inclination of Kepler-17 allows the generation of a star spot model in a sequence of stellar rotation with a period of 12.26 d. Because of the nature of the light curve inversion, the spot model is limited to the equatorial region. We also investigated the starspot lifetimes of Kepler-17 utilizing the MCMC method. Combined with the LIBR inversion results, it was found that the star spots typically last from one to several stellar rotations. From the time evolution of the spot size, a magnetic cycle period of 437 d can be derived. This value is comparatively shorter than the solar cycle which might be a consequence of the younger age (∼ 1.78 Gyr) of Kepler-17. The light curve of Kepler-17 is characterized by the presence of large-amplitude variation caused by star spots but no superflare activity. An interesting possibility is that the magnetic energy stored in the star spot regions could have been constantly dissipated by electrodynamic interaction between the central star and the hot Jupiter, Kepler-17b, via a lower-level energy release process.

Analytical model of the inductor system of the device to prevent ice formation on power lines

The article describes the analytical model of the magnetic-pulsed electromechanical energy converter in relation to the device for preventing ice formation on power lines. The inductor system of the device is a flat inductor and a firing pin made of electrically conductive material. The mobility of both the firing pin, and also the inductor is due to the attachment of the device to the pair of power line wires. This feature, in contrast to the fixed position of the inductor traditionally used, required the development of the universal design scheme for the electrodynamic interaction of the inductor and the firing pin. The proposed analytical model takes into account the forces of resistance to the motion of the inductor system caused by the presence of the elastic return mechanisms in the device and attachment to the power line wire, which is a body with a distributed mass. The developed analytical model was tested. The calculation of the device parameters for the transmission line span with the specified mass-dimensional characteristics was performed.

Engineering couplings for exciton transport using synthetic DNA scaffolds

Summary Control over excitons enables electronic energy to be harnessed and transported for light harvesting and molecular electronics. Such control requires nanoscale precision over the molecular components. Natural light-harvesting systems achieve this precision through sophisticated protein machinery, which is challenging to replicate synthetically. Here, we introduce a DNA-based platform that spatially organizes cyanine chromophores to construct tunable excitonic systems. We synthesized DNA-chromophore nanostructures and characterized them with ensemble ultrafast and single-molecule spectroscopy and structure-based modeling. This synthetic approach facilitated independent control over the coupling among the chromophores and between the chromophores and the environment. We demonstrated that the coupling between the chromophores and the environment could enhance exciton transport efficiency, highlighting the key role of the environment in driving exciton dynamics. Control over excitons, as reported here, offers a path toward the development of designer nanophotonic devices.

All-optical motion control of metal nanoparticles powered by propulsion forces tailored in 3D trajectories

Increasing interest has been drawn to optical manipulation of metal (plasmonic) nanoparticles due to their unique response on electromagnetic radiation, prompting numerous applications in nanofabrication, photonics, sensing, etc. The familiar point-like laser tweezers rely on the exclusive use of optical confinement forces that allow stable trapping of a single metal nanoparticle in 3D. Simultaneous all-optical (contactless) confinement and motion control of single and multiple metal nanoparticles is one of the major challenges to be overcome. This article reports and provides guidance on mastering a sophisticated manipulation technique harnessing confinement and propulsion forces, enabling simultaneous all-optical confinement and motion control of nanoparticles along 3D trajectories. As an example, for the first time to our knowledge, programmable transport of gold and silver nanospheres with a radius of 50 and 30 nm, respectively, along 3D trajectories tailored on demand, is experimentally demonstrated. It has been achieved by an independent design of both types of optical forces in a single-beam laser trap in the form of a reconfigurable 3D curve. The controlled motion of multiple nanoparticles, far away from chamber walls, allows studying induced electrodynamic interactions between them, such as plasmonic coupling, observed in the presented experiments. The independent control of optical confinement and propulsion forces provides enhanced flexibility to manipulate matter with light, paving the way to new applications involving the formation, sorting, delivery, and assembling of nanostructures.

Direct Radio Discovery of a Cold Brown Dwarf

Abstract Magnetospheric processes seen in gas giants such as aurorae and circularly polarized cyclotron maser radio emission have been detected from some brown dwarfs. However, previous radio observations targeted known brown dwarfs discovered via their infrared emission. Here we report the discovery of BDR J1750+3809, a circularly polarized radio source detected around 144 MHz with the Low-Frequency Array (LOFAR) telescope. Follow-up near-infrared photometry and spectroscopy show that BDR J1750+3809 is a cold methane dwarf of spectral type T6.5 ± 1 at a distance of . The quasi-quiescent radio spectral luminosity of BDR J1750+3809 is ≈5 × 1015 erg s−1 Hz−1, which is over two orders of magnitude larger than that of the known population of comparable spectral type. This could be due to a preferential geometric alignment or an electrodynamic interaction with a close companion. In addition, as the emission is expected to occur close to the electron gyrofrequency, the magnetic field strength at the emitter site in BDR J1750+3809 is B ≳ 25 G, which is comparable to planetary-scale magnetic fields. Our discovery suggests that low-frequency radio surveys can be employed to discover substellar objects that are too cold to be detected in infrared surveys.

Electron diffraction by vacuum fluctuations

Vacuum fluctuations are known to produce electron diffraction leading to decoherence and self-interference. These effects have so far been studied as either an extension of the Aharonov–Bohm effect in front of a planar perfect conductor or through path integral analysis. Here, we present a simpler, general, and rigorous derivation based on a direct solution of the quantum electrodynamic aloof interaction between the electron and a material structure in the temporal gauge. Our approach allows us to study dissipative media, for which we show examples of electron wave function shaping due to the interaction with real-metal surfaces. We further present a proof of the relation between the phase associated with vacuum fluctuations and the Aharonov–Bohm effect produced by the image self-interaction that is valid for arbitrary geometries. Besides their fundamental interest, our results could be useful for on-demand patterning of electron beams with potential application in nondestructive nanoscale imaging and spectroscopy.

Effects of Li2O replacing Na2O on glass forming, structure and properties of Na2O–MgO–Al2O3–SiO2 glass and glass-ceramics

Glasses and glass-ceramics in the xLi2O-(5-x)Na2O–20MgO–20Al2O3–54SiO2 system have been prepared by using a conventional melt quenching technology and subsequently a two-step heat-treating method. The effects of Li2O replacing Na2O on crystallization, structural and electrochemical properties of Na2O–MgO–Al2O3–SiO2 glasses and glass-ceramics are studied. The results reveal that the glass forming ability, the bending strength, micro-hardness and ionic conductivity of parent glasses firstly decrease and then increase as Li2O gradually replacing Na2O from 0 mol.% to 5 mol.% due to the disconnection of Si–O–Si network, the suppression of the mobile species and the electrodynamic interaction between the Na–O- and Li–O- oscillating electric dipoles. The main crystalline phase of glass-ceramics is cordierite and the ionic conductivity is three orders of magnitude higher than that glasses. The ionic conductivity of MgO–Al2O3–SiO2 glass-ceramics with 5.0 mol.% Li2O replacing Na2O reaches the highest ionic conductivity (3.4 × 10−6 S/cm), which provides a potential application for glass-ceramics as solid electrolytes in the future.

Determination of the dipole polarizability of the alkali-metal negative ions

We present electric dipole polarizabilities ($\alpha_d$) of the alkali-metal negative ions, from H$^-$ to Fr$^-$, by employing four-component relativistic many-body methods. Differences in the results are shown by considering Dirac-Coulomb (DC) Hamiltonian, DC Hamiltonian with the Breit interaction, and DC Hamiltonian with the lower-order quantum electrodynamics interactions. At first, these interactions are included self-consistently in the Dirac-Hartree-Fock (DHF) method, and then electron correlation effects are incorporated over the DHF wave functions in the second-order many-body perturbation theory, random phase approximation and coupled-cluster (CC) theory. Roles of electron correlation effects and relativistic corrections are analyzed using the above many-body methods with size of the ions. We finally quote precise values of $\alpha_d$ of the above negative ions by estimating uncertainties to the CC results, and compare them with other calculations wherever available.

Fluctuational electrodynamics in atomic and macroscopic systems: van der Waals interactions and radiative heat transfer

We present an approach to describing fluctuational electrodynamic (FED) interactions, particularly van der Waals (vdW) interactions as well as radiative heat transfer (RHT), between material bodies of vastly different length scales, allowing for going between atomistic and continuum treatments of the response of each of these bodies as desired. Any local continuum description of electromagnetic (EM) response is compatible with our approach, while atomistic descriptions in our approach are based on effective electronic and nuclear oscillator degrees of freedom, encapsulating dissipation, short-range electronic correlations, and collective nuclear vibrations (phonons). While our previous works using this approach have focused on presenting novel results, this work focuses on the derivations underlying these methods. First, we show how the distinction between "atomic" and "macroscopic" bodies is ultimately somewhat arbitrary, as formulas for vdW free energies and RHT look very similar regardless of how the distinction is drawn. Next, we demonstrate that the atomistic description of material response in our approach yields EM interaction matrix elements which are expressed in terms of analytical formulas for compact bodies or semianalytical formulas based on Ewald summation for periodic media; we use this to compute vdW interaction free energies as well as RHT powers among small biological molecules in the presence of a metallic plate as well as between parallel graphene sheets in vacuum, showing strong deviations from conventional macroscopic theories due to the confluence of geometry, phonons, and EM retardation effects. Finally, we propose formulas for efficient computation of FED interactions among material bodies in which those that are treated atomistically as well as those treated through continuum methods may have arbitrary shapes, extending previous surface-integral techniques.

Waveguide quantum electrodynamics with superconducting artificial giant atoms.

Models of light-matter interactions in quantum electrodynamics typically invoke the dipole approximation1,2, in which atoms are treated as point-like objects when compared to the wavelength of the electromagnetic modes with which they interact. However, when the ratio between the size of the atom and the mode wavelength is increased, the dipole approximation no longer holds and the atom is referred to as a 'giant atom'2,3. So far, experimental studies with solid-state devices in the giant-atom regime have been limited to superconducting qubits that couple to short-wavelength surface acoustic waves4-10, probing the properties of the atom at only a single frequency. Here we use an alternative architecture that realizes a giant atom by coupling small atoms to a waveguide at multiple, but well separated, discrete locations. This system enables tunable atom-waveguide couplings with large on-off ratios3 and a coupling spectrum that can be engineered by the design of the device. We also demonstrate decoherence-free interactions between multiple giant atoms that are mediated by the quasi-continuous spectrum of modes in the waveguide-an effect that is not achievable using small atoms11. These features allow qubits in this architecture to switch between protected and emissive configurations in situ while retaining qubit-qubit interactions, opening up possibilities for high-fidelity quantum simulations and non-classical itinerant photon generation12,13.

Method for Calculating Radiation Characteristics of Dual-Reflector Antennas with Resonance Size Reflectors of Finite Thickness and Conductivity

The paper presents a method for calculating the radiation patterns (RP) of dual-reflector antenna systems taking into account the electrodynamic interaction between reflectors. This method is suitable for use in the resonance range of wavelengths with respect to the main dimensions of reflectors. The method is based on the iteration procedure proposed by the authors. Each iteration involves the use of the method for calculating the scattering of electromagnetic wave by unclosed screens of finite thickness and conductivity that is suitable for use in resonance range. The specified method is based on applying the E-field integral equation that takes into account the Leontovich approximate boundary conditions on impedance surface and makes it possible to take into account the real thickness and conductivity of antenna’s reflectors. The paper presents the results of calculating RP of dual-reflector antennas built in accordance with the Gregorian scheme for different sizes of small reflector aperture and different arrangements of feeder at the fixed size of large reflector. The paths of reducing the level of the first side lobes of RP are shown. The specified reduction is achieved at the expense of the feeder proper placing with respect to the small reflector of antenna.

Fabrication of optical nanofibre-based cavities using focussed ion-beam milling: a review

Nanofibre-based optical cavities are particularly useful for quantum optics applications, such as the development of integrated single-photon sources, and for studying fundamental light–matter interactions in cavity quantum electrodynamics (cQED). Although several techniques have been used to produce such cavities, focussed ion beam (FIB) milling is becoming popular; it can be used for the fabrication of complex structures directly in the nanofibre. However, it is challenging to mill insulating materials with highly curved geometries and large aspect ratios, such as silica nanofibres, due to charge accumulation in the material. In this article, we highlight the main features of nanofibres and briefly review cQED with nanofibre-based optical cavities. An overview of the milling process is given with a summary of different FIB milled devices and their applications. Finally, we present our technique to produce nanofibre cavities by FIB milling. To overcome the aforementioned challenges, we present a specially designed base plate with an indium tin oxide (ITO)-coated Si substrate and outline our procedure, which improves stability during milling and increases repeatability.