Journal of V. N. Karazin Kharkiv National University. Series Physics

CRYSTAL STRUCTURE, DEFECTS, PINNING AND MAGNETIC FLUX DYNAMICS IN HTNP COMPOUNDS OF THE 1-2-3 SYSTEM (brief review)

2025-10-09T15:39:02+00:00

A brief review of phenomena related to the dynamics of magnetic flux and its pinning in HTSС compounds of the 1-2-3 system is made on the basis of literature data and our own research. The review includes experimental studies of changes in the temperature dependences of electrical resistance and current-voltage characteristics of single crystals of YBa₂Cu₃O_7–δ under the influence of structural defects. Based on the features of the crystal structure of YBa₂Cu₃O_7–δ and typical structural defects of this compound, the dynamics of magnetic flux and the influence of thermal fluctuations on this dynamics, the phase state and dynamics of the vortex system in HTSC compounds of the 1-2-3 system, in particular, pinning of the vortex lattice on defects, intrinsic pinning in the compound YBa₂Cu₃O_7–δ, are considered. In high-temperature superconductors YBa₂Cu₃O_7–δ, the Peak-effect is associated with both the adaptation of the vortex lattice to the pinning potential and the phase transitions from one state of the vortex lattice to another. The Fishtail effect in YBa₂Cu₃O_7–δ can be due to phase transformations of the vortex lattice, the effect of bulk pinning, or the effect of Bean-Livingston surface barriers. The review contains a list of tasks that it is desirable to solve, in particular, the study of pinning and vortex dynamics in YBa₂Cu₃O_7–δ single crystals containing only controlled defects; establishing the role of intergranular bonds in increasing the critical current and effective pinning potential; studying the effect of oxygen vacancy clusters on the Peak-effect.

INFLUENCE OF DECOHERENCE PARAMETERS ON THE EFFICIENCY OF PRESERVING ENTANGLEMENT OF TWO-QUBIT WERNER STATES THROUGH QUANTUM MEASUREMENTS

2025-10-09T15:40:06+00:00

In this work we analyse how a protocol of joint, periodically repeated measurements influences the preservation of state coherence and thereby maintains entanglement in two-qubit systems prepared in a Werner state. By modeling the linear interactions of each qubit with independent dissipative environments (with coefficients , ) together with the dispersive interactions (with coefficients ), we introduce the algorithmic “efficiency” parameter , which quantitatively characterises how strongly these measurements slow down the loss of coherence and support the underlying quantum correlations..

For the maximally entangled input state (Werner state parameter ), the efficiency shows a hyperbolic dependence on the dispersive‐coupling parameter in the strong linear-coupling regime, when , In the opposite regime, when , efficiency asymptotically approaches unity, indicating a loss of capability to suppress decoherence in environments dominated by dispersive interactions. A comprehensive numerical study has been performed on the entanglement-preservation efficiency across all three relevant parameters—namely, the linear and dispersive couplings of each qubit to the environment and the Werner-state parameter that quantifies the initial entanglement. The algorithm’s performance is analyzed in various limiting cases, including the minimal and maximal values of the Werner parameter examined in this work, as well as scenarios in which the linear-interaction strength approaches the dispersive one.

The results obtained indicate that carefully tailored measurement schemes, combined with a high level of quantum-system entanglement, can effectively neutralize the deleterious influence of the environment. This paves the way for formulating detailed, quantitatively substantiated recommendations for tuning dynamic coherence-protection procedures that enhance the reliability of entanglement preservation across a variety of quantum algorithms, including entanglement-based quantum-cryptography protocols (BB84, E91/BBM92, DI-QKD, as well as multi-correlation quantum secret-sharing schemes such as HBB99) and variational algorithms for materials simulation (VQE, ADAPT-VQE, QITE, VQSD and related UCC-based approaches).

MAGNETORESISTANCE OF YBA2CU3-ZALZO7-Δ SINGLE CRYSTALS WITH A SYSTEM OF UNIDIRECT PLANAR DEFECTS

2025-10-09T15:41:21+00:00

The work carried out electroresistive studies under the influence of a constant magnetic field up to 12.7 kOe at the orientation of the magnetic field vector Н ^ с and Н || с on different conductivity regimes of single crystals YBa₂Cu_3-zAl_zO_7-δ (z ≤ 0.5) with a unidirectional system of twin boundaries (TB) at the geometry of the flow of the transport current I || TB, when the influence of twins on the processes of scattering of current carriers is minimized. It was established that twin boundaries in single crystals YBa₂Cu_3-zAl_zO_7-δ (z ≤ 0.5) are effective centers of fluctuation carriers. The deviation from linearity of the dependences of the specific electrical resistance in the base ab-plane ρ_ab(Т) at a temperature T in the interval T_с < T < 1.35 T_с can be satisfactorily explained within the framework of the theory of fluctuation superconductivity. At the same time, in the immediate vicinity of the critical temperature T_c, the fluctuation conductivity (FC) is well described by the three-dimensional Aslamazov – Larkin model. The application of a magnetic field leads to a significant narrowing of the temperature interval of the existence of three-dimensional superconducting fluctuations. The non-monotonic dependence of the coherence length along the c axis at T → 0 x_с(0) on the magnetic field can probably be associated with the suppression of the excess fluctuation conductivity in the region of weak magnetic fields. The absence of the “fan-shaped” expansion of resistive transitions in the magnetic field, characteristic of impurity-free YBa₂Cu_3-zAl_zO_7-δ samples, is due to the suppression of the phase transition to the state of an unpinned vortex liquid due to the enhancement of the pinning of the vortex lattice at the twin boundaries.

STUDY OF THE STRUCTURE OF AMORPHOUS CALCIUM PHOSPHATE BY THE RADIAL DISTRIBUTION FUNCTION OF ATOMS

2025-10-09T15:42:43+00:00

This work presents the results of a study on the structure of amorphous calcium phosphate (ACP), synthesized by precipitation from aqueous solutions with the stoichiometric Ca/P ratios ranging from 1 to 2.13. This material represents an important intermediate phase in the formation of crystalline hydroxyapatite (HA) in solution. At the same time, HA is the main inorganic component of the bone tissue in humans and animals. It is widely used in biomedical technologies. Due to the structural features of amorphous substances, the X-ray diffraction patterns of ACP exhibit broad diffuse maxima, which makes it impossible to use traditional methods of X-ray structure analysis. To obtain detailed information about the spatial arrangement of atoms in ACP samples, a pair distribution function (PDF) was constructed based on experimental X-ray diffraction data processed using the PDFGetX software. The study have been showed that the PDFs of all samples have a similar appearance: the main maxima are located within interatomic distances up to 10 Å, and their positions change only slightly with increasing Ca/P ratio. This indicates that all samples have similar local structure regardless of their chemical composition, synthesis method, precipitation conditions, and processing parameters. Comparison with literature data confirmed the Posner model, according to which both ACP and HA are composed of the same cluster elements – spherical nanoclusters of Ca₉(PO₄)₆.

Thus, even in the amorphous state, ACP exhibits local ordering characteristic of crystalline HA. The obtained results are important for understanding the mechanisms of HA nucleation and growth from the amorphous phase and can be used in the development of new biocompatible materials with controlled properties, particularly in the fields of implantology, orthopedics, regenerative medicine, dentistry, pharmaceutical chemistry, nanotechnology, and bone tissue engineering.

“FRACTALIZATION” OF THE SOLID-STATE PHYSICS

2025-10-09T15:44:49+00:00

It has been demonstrated that in modern solid-state physics, in accordance with the nonlinear and systems paradigms formulated by L. F. Chernogor in the late 1980s, many processes in open, nonlinear, dynamical systems are occurred to be very complex, nonlinear, short-time, ultra-wideband, or fractal.

Moreover, from the point of view of the fractal paradigm put forward in the early 2000s by V. V. Yanovsky, fractality is generally considered as one of the fundamental properties of the surrounding world. Therefore, the study of fractal characteristics, in particular, of natural physical processes and objects in the field of solid-state physics, is appeared to be relevant, interesting, useful and promising.

The main stages of the development of the fractal approach in general are briefly discussed. It is pointed that it was occurred to be too hard to formulate a strict and clear mathematical definition of a fractal. The definition of a fractal been formulated by. K. Falconer and been agreed by the most speciallists as the best for practical usage is considered in detail. Main numerical characteristics of a fractal as well as the modern classification of fractals are considered. The general principal differences existing between the mathematical fractals and physical (or natural) ones as well as between the mono-fractals and the multi-fractals are clearly explained. A review of the main methods for estimating the Hurst fractal dimension is provided.

The main existing directions of "fractalization" of modern solid-state physics are highlighted. Relevant examples are given.

It is noted that images with certain fractal properties play an important role in the "fractalization" of solid-state physics. The use of the two-dimensional Weierstrass function is proposed for modeling images with fractal properties. As an example, the modelling of the unidirectional twin structure observed in the YBa₂Cu₃O_7-δ crystal is considered. A comparison between the model image based on one-dimensional Weierstrass function with defined value of the Hurst fractal dimension and real experimental one is demonstrated.

DISCRETE QND ENTANGLEMENT-PROTECTION PROTOCOL FOR A PHASE-SHIFTED BELL PAIR

2025-10-09T15:46:04+00:00

We evaluate a discrete entanglement-protection protocol for a Bell two-qubit pair undergoing unitary evolution with a single mid-sequence phase change. The test circuit consists of state preparation, a phase shift that does not affect entanglement and emulates a useful quantum gate, and a final standard readout. We compare two variants over a total evolution time of 16 arbitrary time intervals: in the first variant, the phase operation is bracketed by two blocks of five two-qubit QND measurements without readout, while in the baseline variant these measurements are absent. Performance is quantified by the fidelity F, based on the concurrence metric; we take as the minimally acceptable lower bound, below which hardware noise can no longer be safely compensated by the available specialized tools.

Simulations show that the protected scheme maintains throughout the entire observation window, whereas the unprotected scheme, under free evolution in realistic noise regimes encountered in experiments, quickly drops below this threshold even before the gate is applied. These results demonstrate that repeated projective measurements of the entangled state in the Bell basis, implemented as discrete quantum non-demolition (QND) two-qubit measurements without readout, substantially slow the loss of entanglement despite coupling to a thermal bath. The protocol requires fewer measurements, distinguishing it from high-frequency schemes that rely on the Zeno effect.

The approach is directly relevant for fine-tuning superconducting and trapped-ion processors, for pure-state engineering, and for optimizing protocols that use mixed entangled input states. In particular, in these architectures the protocol naturally integrates with existing QND procedures and phase control, providing a means to curb decoherence. Practically, this implies periodic in-operation measurements every 1–2 arbitrary time steps, as well as the possibility of scaling to multi-qubit modules with improved gate fidelities and simplified calibration.

PHYSICAL EXPERIMENT IN DIGITAL REALITY: CHALLENGES OF PRACTICAL ONLINE LEARNING

2025-10-09T15:47:52+00:00

The transition to distance learning in Ukraine – driven by the COVID-19 pandemic, military aggression, mass emigration, and infrastructure disruptions – has created major challenges for physics education, particularly in laboratory training. Traditional physics labs require specialized equipment, which is often inaccessible in remote settings, thus limiting students' opportunities for hands-on experimental experience. Virtual labs and simulations offer a partial solution but face limitations, such as the inability to fully replicate real conditions and the need for interdisciplinary development.

This article presents an adapted approach to remote laboratory work, using the experiment “Weiss Molecular Field” as an example. Originally performed with a pendulum magnetometer, the revised version engages students in calculating and plotting the temperature dependence of spontaneous magnetization in nickel using the Weiss molecular field theory. Students compare theoretical predictions for quantum numbers J = 1/2, 1, and ∞ with experimental data from the literature. Calculations are performed using MS Excel and the GRG optimization method. The results show qualitative agreement with experimental curves, particularly for J = 1/2, which supports the interpretation that electron spins are the primary magnetic carriers in nickel. At low temperatures, Bloch’s spin-wave theory better matches experimental results than the Weiss model, while near the Curie temperature, deviations from theory are observed.

This adapted lab demonstrates that analytical and computational tasks can effectively substitute for direct experimentation in distance learning. The approach develops skills in theoretical analysis, data comparison, and scientific computing. Video tutorials, Excel templates, and interactive visualizations support transparent assessment and active engagement. Surveys revealed a 12% increase in average performance compared to in-person lab versions, along with improved motivation and deeper conceptual understanding. This method is a viable alternative for physics education in resource-limited contexts and can be extended to other lab-intensive disciplines. It also lays the groundwork for a digital lab curriculum that ensures educational continuity during crises.

TRANSFORMING PHYSICS EDUCATION WITH NEURAL NETWORKS: MODERN APPROACHES AND TOOLS

2025-10-09T15:49:14+00:00

This article explores the current trend of using neural networks in teaching physics at the university level. The topic's relevance stems from the need to transform traditional teaching methods to meet the expectations of a new generation of students accustomed to interactive formats and digital technologies. The study aims to analyze modern neural network technologies employed in teaching various sections of physics, evaluate their effectiveness, and outline prospects for further development in this area. The research is based on a review of scientific publications on the subject and practical experiences of implementing neural network technologies in leading universities worldwide. The methodology involves systematic analysis, comparison, and generalization of existing neural network solutions. A detailed analysis of specific neural network technologies applied to different branches of physics is presented: long short-term memory (LSTM) and convolutional neural networks (CNN) for mechanics; generative adversarial network (GAN) and graph neural networks (GNN) for electromagnetism; deep reinforcement learning network (DRL) for thermodynamics; variational autoencoders network (VAE) and residual network (ResNet) for quantum physics; and deep convolutional networks and transformers for astrophysics.

The results demonstrate that implementing neural network technologies significantly enhances learning efficiency, facilitates the visualization of complex physical processes, automates computations, and enables personalized learning. It has been established that the application of various neural network architectures in the educational process fosters the development of critical thinking, a deeper understanding of physical concepts, and practical data-handling skills among students. Promising directions for further development include the creation of multimodal systems, the development of adaptive learning platforms, and the integration of virtual reality with neural network models.

METHODOLOGY FOR CREATING AN INTEGRATED RESEARCH ENVIRONMENT BASED ON JUPYTER NOTEBOOK USING NEURAL NETWORKS

2025-10-09T15:50:27+00:00

This paper presents a methodology for creating an integrated research environment for experimental data processing based on Jupyter Notebook with the use of artificial intelligence tools, particularly generative neural networks. Jupyter Notebook is a leading platform among researchers due to its flexibility, broad library ecosystem, and ease of integration with various analytical tools. Its primary purpose is to enable researchers to create customized software solutions by writing code in more than 40 programming languages.

Traditionally, the development of research tools in Jupyter Notebook requires coding in the Python programming language. However, this can pose challenges for specialists who lack deep programming skills. With the rapid development of generative neural networks, a unique opportunity has emerged to create small, specialized programs for personal use without significant immersion in coding. Moreover, this approach not only simplifies the creation of applied software but also significantly accelerates the acquisition of programming skills, lowering the entry barrier into the development profession.The paper reviews the key capabilities of Jupyter Notebook, provides a brief overview of its interface, and offers basic explanations of the principles of program creation using neural networks. A crucial step in building research tools is the formulation of software functionality and interface design. Given that code generation is performed using neural networks, particular attention is paid to prompt engineering principles for effective code generation and the creation of applications for automating the processing of data in various formats. Specific examples of functional module development are presented, demonstrating the adaptability of neural network models to address typical experimental data processing tasks. The article is intended for experimental researchers seeking to enhance their analytical capabilities using modern neural network technologies while avoiding complex programming.

USING WOLFRAM MATHEMATICA SOFTWARE ENVIRONMENT TO PROCESS THE RESULTS OF THE LABORATORY WORK “NEWTON'S RING”

2025-10-09T15:51:53+00:00

This article deals with the urgent problem of introducing modern information technologies into the physics workshop, which increases the efficiency of the educational process and contributes to the formation of students' research competencies. The aim of the study is to analyze the capabilities of the Wolfram Mathematica software environment for processing and visualizing the results of interference experiments on the example of the laboratory work “Newton's Rings”. The research methods include theoretical analysis of interference phenomena, computer modeling in the Wolfram Mathematica software environment, and the use of interactive demonstrations of the Wolfram Demonstrations Project. An algorithm for processing experimental data is proposed, which allows the automation of calculations and improves their accuracy. The results of the study are presented in the form of a mathematical model of Newton's rings, which provides a visualization of the interference pattern and allows studying the dependence of its characteristics on various physical parameters of the system. Methodical recommendations for integrating Wolfram Mathematica software environment into a laboratory physics workshop have been developed. It is proved that the use of this software contributes to the development of skills in working with modern software tools, stimulates students' research activities, and provides interdisciplinary links between physics, mathematics, and computer science. The implementation of the proposed methodology allows the preparation of future specialists for professional activities in the context of the digital transformation of science and education. The paper highlights the pedagogical value of the Wolfram Demonstrations Project as an accessible and interactive supplement to theoretical instruction and physical experimentation. The results confirm that incorporating Wolfram Mathematica into the laboratory framework supports the development of digital competencies, critical thinking, and a research-oriented mindset. Ultimately, the implementation of this methodology prepares students for professional scientific work in an era of digital transformation in science and education.

M. D. PYLCHIKOV'S CONTRIBUTION TO THE DEVELOPMENT OF NEW PHYSICAL DEVICES AND TO THE SUPPLEMENTATION OF COLLECTIONS OF DEVICES OF PHYSICAL CABINETS AND LABORATORIES OF KHARKIV AND ODESSA UNIVERSITIES AND KHARKIV TECHNOLOGICAL INSTITUTE

2025-11-17T07:43:29+00:00

The article summarizes information about the activities of M. D. Pylchykov, aimed at developing of new physical devices, as well as replenishing of the devices collections that were used in physics cabinets, in educational and research laboratories of Kharkiv and Odessa Universities and the Kharkiv Institute of Technology. M. D. Pylchykov corresponded with the heads of companies that manufactured educational and scientific equipment, purchased devices from them, and ordered devices of his own design for manufacture. M. D. Pylchykov developed a number of new devices and improved some of the existing ones. He made a significant contribution to replenishing of the collection of the physics department of Kharkiv University with instruments and equipment. In 1891, on his initiative, a magnetic and meteorological department of the physics department and a meteorological station were created and equipped with instruments at Kharkiv University. During the Odessa period of his activity, M. D. Pylchikov organized a measuring laboratory at Odessa University. During the time that M. D. Pylchykov worked at the Kharkiv Institute of Technology, the physics room, physics laboratory, and meteorological observatory of the institute were significantly replenished with instruments and the latest scientific equipment. The article analyzes the data obtained as a result of a purposeful search, study, identification, and restoration of a number of physical devices that were probably purchased by M. D. Pylchykov for his physical offices and laboratories and which he could have used during classes and research.