arXiv subjects

Mikhail Maslov

Publications and source records attributed to Mikhail Maslov.

12 recordsLinked to original sources

arXiv2025

The R-index: A universal metric for evaluating OAM content and mode purity in optical fields

Despite its pivotal role in optical manipulation, high-capacity communications, and quantum information, a general measure of orbital angular momentum (OAM) in structured light remains elusive. In optical fields, where multiple vortices coexist, the local nature of vortex OAM and the absence of a common rotation axis make the total OAM of the field difficult to quantify. Here, we introduce the R-index, a metric that captures the intrinsic OAM content of any structured optical field, from pure Laguerre-Gaussian modes to arbitrary multi-vortex superpositions. Not only does this metric quantify the total OAM, it also assesses field purity, providing insight into the fidelity and robustness of the OAM generation. By unifying OAM characterization into a single figure of merit, the R-index enables direct comparison across diverse beam profiles and facilitates the identification of optimal configurations for both foundational studies and applied technologies.

physics.optics↗

arXiv2025

Bottom-up Analysis of Ro-Vibrational Helical Dichroism

Helical dichroism (HD) is a proposed method for the resolution of molecular chirality, employing the orbital angular momentum (OAM) of light. Going beyond the conventional assumptions about HD, this work proposes a rigid theoretical framework for the analysis of the HD, based on molecular symmetries and rotational eigenstates. We derive the rotational selection rules, which clearly establish that HD only emerges from the spin-orbit coupling of light, even for beams without far-field OAM. Our findings refine the conditions for observing HD, shedding light on the outcome of prior experiments and guiding future designs for chiral sensing using structured light.

physics.atom-ph↗

arXiv2024

Massive Dirac-Pauli physics in lead-halide perovskites

In standard quantum electrodynamics (QED), the so-called non-minimal (Pauli) coupling is suppressed for elementary particles and has no physical implications. Here, we show that the Pauli term naturally appears in a known family of Dirac materials -- the lead-halide perovskites, suggesting a novel playground for the study of analogue QED effects. We outline measurable manifestations of the Pauli term in the phenomena pertaining to (i) relativistic corrections to bound states (ii) the Klein paradox, and (iii) spin effects in scattering. In particular, we demonstrate that (a) the binding energy of an electron in the vicinity of a positively charged defect is noticeably decreased due to the polarizability of lead ions and the appearance of a Darwin-like term, (b) strong spin-orbit coupling due to the Pauli term affects the exciton states, and (c) scattering of an electron off an energy barrier with broken mirror symmetry produces spin polarization in the outgoing current. Our study adds to understanding of quantum phenomena in lead-halide perovskites, and paves the way for tabletop simulations of analogue Dirac-Pauli equations.

cond-mat.mes-hall↗

arXiv2023

Theory of angular momentum transfer from light to molecules

We present a theory describing interaction of structured light, such as light carrying orbital angular momentum, with molecules. The light-matter interaction Hamiltonian we derive is expressed through couplings between spherical gradients of the electric field and the (transition) multipole moments of a particle of any non-trivial rotation point group. Our model can therefore accommodate for an arbitrary complexity of the molecular and electric field structure, and can be straightforwardly extended to atoms or nanostructures. Applying this framework to ro-vibrational spectroscopy of molecules, we uncover the general mechanism of angular momentum exchange between the spin and orbital angular momenta of light, molecular rotation and its center-of-mass motion. We show that the non-zero vorticity of Laguerre-Gaussian beams can strongly enhance certain ro-vibrational transitions that are considered forbidden in the case of non-helical light. We discuss the experimental requirements for the observation of these forbidden transitions in state-of-the-art spatially-resolved spectroscopy measurements.

physics.atom-ph↗

arXiv2022

Implementation of AI/Deep Learning Disruption Predictor into a Plasma Control System

This paper reports on advances to the state-of-the-art deep-learning disruption prediction models based on the Fusion Recurrent Neural Network (FRNN) originally introduced a 2019 Nature publication. In particular, the predictor now features not only the disruption score, as an indicator of the probability of an imminent disruption, but also a sensitivity score in real-time to indicate the underlying reasons for the imminent disruption. This adds valuable physics-interpretability for the deep-learning model and can provide helpful guidance for control actuators now that it is fully implemented into a modern Plasma Control System (PCS). The advance is a significant step forward in moving from modern deep-learning disruption prediction to real-time control and brings novel AI-enabled capabilities relevant for application to the future burning plasma ITER system. Our analyses use large amounts of data from JET and DIII-D vetted in the earlier NATURE publication. In addition to when a shot is predicted to disrupt, this paper addresses reasons why by carrying out sensitivity studies. FRNN is accordingly extended to use many more channels of information, including measured DIII-D signals such as (i) the n1rms signal that is correlated with the n =1 modes with finite frequency, including neoclassical tearing mode and sawtooth dynamics, (ii) the bolometer data indicative of plasma impurity content, and (iii) q-min, the minimum value of the safety factor relevant to the key physics of kink modes. The additional channels and interpretability features expand the ability of the deep learning FRNN software to provide information about disruption subcategories as well as more precise and direct guidance for the actuators in a plasma control system.

physics.plasm-ph↗

arXiv2021

Impurity with a resonance in the vicinity of the Fermi energy

We study an impurity with a resonance level whose energy coincides with the Fermi energy of the surrounding Fermi gas. An impurity causes a rapid variation of the scattering phase shift for fermions at the Fermi surface, introducing a new characteristic length scale into the problem. We investigate manifestations of this length scale in the self-energy of the impurity and in the density of the bath. Our calculations reveal a model-independent deformation of the density of the Fermi gas, which is determined by the width of the resonance. To provide a broader picture, we investigate time evolution of the density in quench dynamics, and study the behavior of the system at finite temperatures. Finally, we briefly discuss implications of our findings for the Fermi-polaron problem.

cond-mat.quant-gas↗

arXiv2020

All-nitrogen cages and molecular crystals: Topological rules, stability, and pyrolysis paths

We have combined ab initio molecular dynamics with the intrinsic reaction coordinate in order to investigate the mechanisms of stability and pyrolysis of N$_{4}$-- N$_{120}$ fullerene-like nitrogen cages. The stability of the cages was evaluated in terms of the activation barriers and the activation Gibbs energies of their thermal-induced breaking. We found that binding energies, bond lengths, and quantum-mechanical descriptors failed to predict the stability of the cages. However, we derived a simple topological rule that adjacent hexagons on the cage surface resulted in its instability. For this reason, the number of stable nitrogen cages is significantly restricted in comparison with their carbon counterparts. As a rule, smaller clusters are more stable, whereas earlier proposed rather large cages collapse at room temperature. The most stable all-nitrogen cages are N$_{4}$ and N$_{6}$ clusters, which can form the van-der-Waals crystals with the densities of 1.23 and 1.36 g/cm$^{3}$, respectively. Examination of their band structures and densities of electronic states shows that they are both insulators. Their power and sensitivity are not inferior to the modern advanced high-energy nanosystems.

cond-mat.mtrl-sci↗

arXiv2020

Synthetic spin-orbit coupling mediated by a bosonic environment

We study a mobile quantum impurity, possessing internal rotational degrees of freedom, confined to a ring in the presence of a many-particle bosonic bath. By considering the recently introduced rotating polaron problem, we define the Hamiltonian and examine the energy spectrum. The weak-coupling regime is studied by means of a variational ansatz in the truncated Fock space. The corresponding spectrum indicates that there emerges a coupling between the internal and orbital angular momenta of the impurity as a consequence of the phonon exchange. We interpret the coupling as a phonon-mediated spin-orbit coupling and quantify it by using a correlation function between the internal and orbital angular momentum operators. The strong-coupling regime is investigated within the Pekar approach and it is shown that the correlation function of the ground state shows a kink at a critical coupling, that is explained by a sharp transition from the non-interacting state to the states that exhibit strong interaction with the surroundings. The results might find applications in such fields as spintronics or topological insulators, where spin-orbit coupling is of crucial importance.

cond-mat.quant-gas↗

arXiv2019

Silicon rebirth: Metallic prismane allotropes of silicon for the next-gen technologies

We report the prediction of metallic quasione-dimensional $sp^{3}$-hybridized silicon allotropes in the form of prismanes. Silicon prismanes or polysilaprismanes are the silicon nanotubes of a special type constructed from the dehydrogenated molecules of cyclosilanes (silicon rings). By means of density functional theory the electronic, geometry, energy, and some mechanical properties of these tubes were investigated. Our results show that silicon polyprismanes are thermodynamically stable compounds, and the character of the energy spectrum, as well as the behavior of transmission function near the Fermi level, show that they exhibit non-typical for the silicon systems metallic nature. Moreover, the metallic state of polysilaprismanes is resistant to the mechanical stresses applied along their main axis. Unusual properties predicted in the presented study discover new prospects of application of silicon nanostructures as the basic elements of future micro- and nanoelectronics, as well as in energy, metrology, medical, and information technologies.

cond-mat.mtrl-sci↗

arXiv2016

Stone-Wales defects in nitrogen-doped C$_{20}$ fullerenes: Insight from $\textit{ab initio}$ calculations

Density functional theory is applied to study the mechanism of the Stone-Wales defect formation in pure and nitrogen-doped dodecahedral C$_{20}$ fullerenes. The molecular structures of initial and defected cages as well as transition states dividing them are obtained. Depending on the number of nitrogen atoms and their relative position in the cage, Stone-Wales defect is formed through the single additional intermediate state or directly. The activation energy barrier of the defect formation reduces from 4.93 eV in pure C$_{20}$ to 2.98 eV in single-doped C$_{19}$N, and reaches $\sim$ 2 eV under further doping. All nitrogen-doped fullerenes considered possess high kinetic stability at room temperature. However, they become much less stable at temperatures of about 750 K that are typical for the fullerene annealing process.

cond-mat.mes-hall↗

arXiv2016

Toward CL-20 crystalline covalent solids: On the dependence of energy and electronic properties on the effective size of CL-20 chains

One-dimensional CL-20 chains have been constructed using CH$_2$ molecular bridges for the covalent bonding between isolated CL-20 fragments. The energy and electronic properties of the nanostructures obtained have been analyzed by means of density functional theory and nonorthogonal tight-binding model considering Landauer-Büttiker formalism. It has been found that such systems become more thermodynamically stable as the efficient length of the chain increases. Thus, the formation of bulk covalent CL-20 solids may be energetically favorable, and such structures may possess high kinetic stability comparing to the CL-20 molecular crystals. As for electronic properties of pure CL-20 chains, they are wide-bandgap semiconductors with energy gaps equal to several electron volts that makes their use in nanoelectronic applications problematic without any additional modification.

cond-mat.mes-hall↗

arXiv2012

Large-scale drifts observed on electron temperature measurements on JET plasmas

Between 1995 and 2009, electron temperature (Te) measurements of more than 15000 plasmas produced in the Joint European Torus (JET) have been carefully reviewed using the two main diagnostics available over this time period: Michelson interferometer and Thomson scattering systems. Long term stability of JET Te is experimentaly observed by defining the ECE TS ratio as the ratio of central Te measured by Michelson and LIDAR. This paper, based on a careful review of Te measurement from 15 years of JET plasmas, concludes that JET Te exhibits a 15-20% effective uncertainty mostly made of large-scale temporal drifts, and an overall uncertainty of 16-22%. Variations of 18 plasma parameters are checked in another data set, made of a "reference data set" made of ohmic pulses as similar as possible between 1998 and 2009. Time drifts of ECE TS ratios appear to be mostly disconnected from the variations observed on these 18 plasma parameters, except for the very low amplitude variations of the field which are well correlated with off-plasma variations of a 8-channel integrator module used for measuring many magnetic signals from JET. From mid-2002 to 2009, temporal drifts of ECE TS ratios are regarded as calibration drifts possibly caused by unexpected sensitivity to unknown parameters; the external temperature on JET site might be the best parameter suspected so far. Off-plasma monitoring of MI made of calibration performed in the laboratory are reported and do not appear to be clearly correlated with drifts of ECE TS ratio and variations of magnetics signals integrators. Comparison of estimations of plasma thermal energy for purely Ohmic and NBI-only plasmas does not provide any definite information on the accuracy of \mi or \lidar measurements. Whatever causes these Te drifts, this experimental issue is regarded as crucial for JET data quality.

physics.plasm-ph↗