Physics of Wave Processes and Radio Systems

Background. The study of entangled states in Jaynes–Cummings models and its multiqubit generalizations and extensions remains an important and relevant topic in modern quantum optics, quantum information science and solid state physics. This is due to the fact that such models naturally describe the dynamics of interaction of logical elements of quantum devices, such as quantum computers or quantum networks (qubits) with microwave fields of resonators used to control the states of qubits. In this regard, it is very important to search for the most efficient schemes of generation, control and monitoring of entangled qubit states within the framework of Jaynes–Cummings type models. Aim. To investigate the entanglement dynamics of a pair of qubits, each of which is locked in a single-mode resonator and interacts non-resonantly with the vacuum field mode, in the presence of detuning between frequencies of transitions in the qubits and frequencies of resonator modes and dipole-dipole interaction of the qubits. Methods. To analyze the dynamics of the considered system, the solution of the time-dependent quantum Schrödinger equation is investigated. The exact solution of the above equation in the case of entangled Bell-type initial qubits states is found. This is used to calculate the criterion of entanglement of a pair of qubits – negativity. Numerical modeling of the time dependence of negativity for different values of the parameters of the considered model has been carried out. Results. It is shown that the presence of detuning, the difference in the qubit-photon couplings and the intensity of the dipole-dipole interaction significantly affect the maximum degree of entanglement of the qubit subsystem during its evolution. It is found that for certain parameters of the model under consideration, the initial Bell entangled states of qubits can be considered as long-lived stable states. Conclusion. The possibility of realization of long-lived and robust two-qubit entangled states in the system under consideration has been established. The obtained results can be used for effective control and manipulation of the degree of entanglement of qubits interacting with microwave fields of resonators.

Background. Based on the results of the operation of various engineering products, it has been established that the individual features of the microreliefs of their working surfaces largely determine their reliability and durability. In this regard, the development of modern new methods for measuring the roughness parameters of a microrelay for their further use in mechanical engineering is an urgent task at the present time. Aim. The aim of the work is to study and develop an optoelectronic method, new algorithms and software for digital image processing of the studied microreliefs of the mihanic treated surfaces, as a result of which the parameters of the roughness of microreliefs are measured directly during the technological process. Methods. The method is based on computer processing of images of the studied microreliefs. The essence of the method is that the lines of video signals of the microrelief image are considered as the realizations of a random stationary process. Herewith the full Image consists of m such realizations – the number of lines of the image. The number of pixels in the row n corresponds to the width of the image being analyzed. As a result of such image processing, a string matrix of correlation coefficients is obtained, a correlation function, to which the well-known mathematical methods of processing a stationary random process are then applied to find its normalized autocorrelation function. Further, to increase the resolution of the correlation method for estimating the microrelief parameters, spectral analysis of the obtained autocorrelation functions was used. Based on the results of the spectral analysis, the roughness of the studied microrelief is determined with a given probability. Results. A correlation-spectral method for measuring the parameters of microrelief has been developed, which is based on the representation of a halftone image of the surface under study as a set of implementations of a stationary random process. For this representation, correlation functions for the studied microreliefs were calculated and spectral densities for them were determined. It has been established that microreliefs with different roughness differ significantly in spectral densities. The results of applying this method to estimating the parameters of the microrelief of the inner ring of the bearing are presented. Conclusion. The prospects of using the optoelectronic method and digital processing of images of microreliefs of mechanically processed surfaces in order to quickly measure their roughness parameters are shown. An algorithm for calculating the autocorrelation function characterizing the microrelief under study as a set of implementations of a random stationary process, where each implementation is a line of a video signal, has been developed. Then, to increase the resolution of the method, the Fourier transform is applied to the obtained autocorrelation functions and the spectral densities of the autocorrelation functions are calculated. The method of least squares is used to construct the dependence which is used to measure the roughness of the studied microrelief.

Background. The relevance of the topic of this work is due to the need to reduce the complexity of the process of designing the topology of boards of film nodes of radio frequency and microwave paths. Aim. Development of a methodology for modeling and synthesizing parameters of film assemblies of radio frequency and microwave paths of electronic equipment based on the upgraded AWR Microwave Office Environment 15 design environment. Methods. The article discusses a method for synthesizing board topology, which includes the following basic operations and procedures: setting up test benches, analyzing source data, estimating required electrical parameter values, adaptive grid partitioning, modeling multiplexed signals, modeling element distortions, routing circuit tracing, verifying solutions using tables, evaluating a completed project using test benches, minimizing the distances between conductors, plotting and optimizing graphs. Development of the conductor methodology using the example of modeling and design of a directional loop coupler of RF and MV paths. Results. The topology of a directional loop coupler with a 10 GHz signal frequency has been synthesized for its implementation using thick-film technology on a 0,25 mm thick polycor and Du Pont 951 substrate. The frequency response of the coupler is built. Conclusion. The resulting topology meets the requirements of the technical specification. Experimental testing of the technique has shown that it can reduce the complexity of modeling the main characteristics of nodes by 20–40 % and reduce information resources by up to 30 %.

Background. The work is aimed at the development and research of technological processes and production operations for the manufacture of printed antennas. A special case of such antennas is a flat spiral antenna with additional deceleration in the form of a dielectric or metal-dielectric plate. Aim. The paper analyzes the distinctive features of the manufacturing processes of flat spiral antennas with additional deceleration. A number of «bottlenecks» in production operations are identified, related to the specifics of the basic materials and basic industrial technologies used. Methods. The research is based on a practice-oriented comparison of technological processes for manufacturing flat spiral antennas with additional deceleration with various design solutions of the decelerating structure: planar dielectric plate, planar metal-dielectric plate with metallized holes, planar metal-dielectric plate with metal pins. The basic technologies used are the combined positive method of PCB production, the technology of pressing multilayer printed circuit boards, the technology of assembly and electrical installation of microwave devices. Results. Design options for planar deceleration plates and the corresponding technological processes of their production are proposed, their key differences are identified: manufacturability, degree of automation, duration. Conclusion. From a practical point of view, it is shown that the design of the dielectric retarding plate is the most technologically advanced and commercially suitable for mass production, which is confirmed by the manufactured samples. If it is necessary to integrate additional retarding elements into the design of the PO, the option with metallized holes is more technologically advanced.

Background. The generation and development of experimental facilities for research in the field of near-Earth plasma physics is an extremely urgent task. The Sura short-wave heating stand is the only operating mid-latitude research facility in the world on the active effect on the Earth’s ionosphere. The new physical results obtained at the HAARP, which has a higher transmitter radiation power, stimulate work to assess the possibilities of upgrade and determine the achievable parameters of near-Earth plasma perturbations for other facilities including the Sura stand. Aim. Numerical simulation and analysis of achievable parameters of large-scale thermal disturbances of near-Earth plasma during facility upgrading and promising power levels implementation of the Sura stand. Methods. The simulation was conducted using open source SAMI2 code supplemented by an upgraded heating source model using direct calculation of the abnormal absorption coefficient to approximate the cold plasma at the Gaussian spectrum of elongated inhomogeneities. Results. Exposure results for both daytime and late evening hours were investigated. For daytime conditions it was obtained that the promising power levels implementation at the Sura facility results in an almost twofold increase of the density and electrons temperature perturbations in the artificial duct region at the Earth’s outer ionosphere heights. For late evening conditions it is obtained that the upgrade of the heating facility also results in a twofold increase of electron temperature perturbations. At the same time, the increase of the electron density relative perturbations level is not so significant and at most 20% relative to the actual facility characteristics. Conclusion. It has been shown that the generated thermal perturbation parameters are non-linearly dependent on the radiation power of the pump wave and their growth is saturated due to the plasma redistribution in the abnormal absorption region.