Vol 26, No 2 (2023)

Background. Interest in the study of entangled states of systems of natural and artificial atoms (qubits) interacting with selected modes of microwave resonators is associated with their use as logic elements of quantum computers. At the same time, the most important task of the physics of quantum computing is the choice of the most effective mechanisms for manipulating and controlling the entangled states of qubits in such devices. Aim. The dynamics of the entanglement of two dipole-coupled superconducting Josephson qubits induced by a thermal noise of a coplanar resonator is studied for various initial states of the qubits. Methods. Based on the exact solution of the quantum Liouville equation for the whole density matrix of the system under consideration, the time behavior of the qubit entanglement parameter (negativity) is found for chaotic thermal, pure separable, and entangled initial states of qubits. Results. It is shown that the entanglement of qubits induced by the thermal noise of the resonator is possible for both the chaotic thermal states and separable states of qubits, except the case when both qubits are excited. It has also been found that, for small values of the dipole–dipole interaction parameter, taking this interaction into account leads to an increase in the degree of entanglement. For values of the dipole-dipole interaction parameter greater than some limit value, the opposite effect takes place. It is found that for entangled initial states of qubits, the inclusion of direct interaction has a small effect on the entanglement dynamics. It is shown that the initial coherence of qubit states can lead to a significant increase in the degree of their entanglement in the presence of a dipole–dipole interaction. Conclusion. The dipole-dipole interaction can be used as an effective mechanism for qubits entanglement manipulation and controlling.

Background. Symmetric slot lines on a perfectly reflecting half-plane are good mathematical models for slot antennas on an ideal plane of finite dimensions, which in practice have a high gain and operate over a wide frequency band. These antennas are used in ultra-fast information processing systems based on microwave and optical volume integrated circuits. Aim. The work presents a solution to the problem of radiation of a perfectly reflecting half-plane, which was excited by a symmetric slot line with a different law of slot expansion. Methods. The problem was solved by the Fourier variable separation method, by which the Green tensor function was obtained, which connects the two components of the antenna radiation field with the excitation field in the gap. Results. It is shown that in the far zone, the radiation field of an ideally reflecting half-plane has two components: the main and crosspolarization. The Green tensor function has a complex form and consists of two terms. The analysis of the Green tensor function shows the participation of each term in the formation of a field in the far zone, demonstrates the mechanism of radiation and leads to known special cases for slot radiators. Conclusion. The validity of the presented mathematical model is confirmed by experimental research.

Background. To improve the accuracy of navigation and radar systems, functional nodes of the EHF wavelength range are used. At the same time, an increase in the operating frequency increases the requirements for the accuracy of manufacturing and docking devices. Analysis of the propagation of electromagnetic waves, subject to the presence of defects in the waveguide paths, will allow determining sufficient manufacturing accuracy and evaluating physical processes in an irregular area. Aim. The aim of this work was to study the effect of sharp irregularities on the characteristics of the digital twin of a broadband shielded dielectric waveguide operating in the frequency range from 90 to 100 GHz. Methods. Using a numerical experiment, two variants of irregularity were investigated. They are presented in the form of displacement of sections of shielded dielectric waveguides in the vertical and horizontal planes. Results. According to the values of the transfer characteristic of the waveguide path, the regularities of the attenuation of the electromagnetic wave energy from the magnitude of the irregularity are revealed and the permissible manufacturing accuracy is proposed. Conclusion. To solve the problems of sewerage of weak signals, the authors recommend using a non-jointed manufacturing technology.

Background. The problem of satellite navigation signals’ jamming-protected receivers design is quite relevant due to the high vulnerability of such signals to the influence of interferences whose sources number is constantly increasing. Aim. To design a space-time adaptive filter and to implement its work in real-time as a part of jamming-protected satellite navigation system. Methods. The space-time filtering method fitted for the real-time realization is obtained based on the satellite signal space processing algorithm. The apparatus chosen for the satellite navigation signals reception, the filtering algorithm practical realization and the processed signal demodulation is described. The computer modeling of the signals records filtering and demodulation using the obtained algorithm as well as the real-time experiments in satellite signals processing with different numbers of outer jammers using the constructed jamming-protected receiver are carried out. Results. As a result of modeling and experiments with the designed set the values of performance characteristics of the jamming-protected navigation system are yielded which correspond to a good quality solution of the interference mitigation problem in a satellite navigation signal. Conclusion. The digital processing model based on the obtained space-time filter adequately describes the interference mitigation process in a real satellite signal. The obtained jamming-protected satellite navigation signal receiver is functional and can be used in practice.