arXiv subjects

Mihail Petrov

Publications and source records attributed to Mihail Petrov.

At least 19 recordsLinked to original sources

arXiv2026

Mie Optical Computing

Optical computing is emerging as a promising paradigm for next-generation information processing. Diffractive optical processors rely on spatially distributed trainable degrees of freedom, leading to extended architectures. Here, we propose a compact neuromorphic optical-computing approach where the entire trainable transformation is implemented by a single Mie scatterer. By formulating computation in vector spherical harmonics basis, trainable modal couplings can be concentrated within a finite object through its T-matrix. Since available T-matrix parameters scale as the fourth power of maximal multipole order, this architecture can overcome trainable-parameter-density limitations of conventional spatially distributed diffractive processors. We demonstrate classification of phase-encoded MNIST images using scattered-field intensity. At a particle size parameter of $ka = 15$, the trained T-matrix reaches approximately 90% test accuracy, comparable to a single-layer artificial neural network. Similar performance can be achieved using near-fields, enabling on-chip integration. We show how reciprocity, passivity, and particle symmetry constrain performance: passivity reduces the accessible operator space while improving robustness, whereas symmetry reduces the number of independent parameters. Finally, we inverse-design a non-absorbing dielectric scatterer that realizes the classification task with 84% accuracy. These results demonstrate that nontrivial neuromorphic transformations can be encoded within the multipolar response of a single compact scatterer.

physics.optics↗

arXiv2026

Optical Theorem for Measuring the Acoustic Extinction Cross Section of Helmholtz Resonators

The optical theorem is a powerful tool of scattering theory that directly relates the extinction cross section of a scatterer to its forward scattering amplitude. While widely used in electromagnetism and optics, its application in acoustics has remained limited, primarily due to experimental challenges. These include the finite size of practical sound sources and the stringent requirements for detecting weak scattered signals. In this work, we analyze these limitations and develop a robust methodology for measuring the acoustic extinction cross section under realistic conditions, including non-ideal anechoic environments. The approach is applied experimentally to a Helmholtz resonator in an imperfect anechoic environment with standing-wave resonances. The retrieved extinction cross section exhibits a single pronounced resonance near 2000 Hz. The resonance position, peak magnitude, and spectral lineshape are consistent with full-wave numerical simulations. The results demonstrate that, when combined with appropriate data processing, the optical theorem provides a simple and reliable tool for characterizing acoustic resonators, opening new opportunities for quantitative analysis of acoustic scattering and absorption phenomena.

physics.class-ph↗

arXiv2026

Resonant state expansion for acoustic resonators. Part I. Eigenvalue problem

Resonant-state expansion (RSE) is a powerful modal framework for the perturbative analysis of open resonant systems, providing direct access to complex eigenfrequencies and eigenmodes. While RSE is well developed in electromagnetism, a comparably systematic formulation for acoustics remains less established. Here, we develop a general Green-function-based formalism for acoustic RSE and illustrate it for a class of two-dimensional acoustic resonators. Using the resonant states of an analytically solvable cylindrical reference system as a basis, we derive explicit perturbation matrix elements for uniform, radial, and sectoral variations of density and compressibility, representing homogeneous tuning, graded profiles, and symmetry-induced modal coupling. The resulting complex eigenfrequencies and eigenmodes are validated against exact analytical solutions and finite-element simulations, showing excellent quantitative agreement. The framework provides a systematic and physically transparent approach for analyzing perturbed open acoustic resonators and establishes a basis for resonant-state methods in acoustic metamaterials and non-Hermitian acoustics.

physics.comp-ph↗

arXiv2026

Resonant state expansion for acoustic resonators. Part II. Scattering problem

We develop a resonant-state expansion formulation for acoustic scattering by individual resonators. The scattered pressure and particle-velocity fields are expanded over the resonant states of the system, with excitation amplitudes determined by overlap integrals between the incident field and the resonant states over the resonator volume. Using the acoustic energy flux, we derive expressions for the extinction, scattering, and absorption cross-sections and show that the extinction spectrum can be resolved into contributions from individual resonant states. The formulation is first validated for a homogeneous two-dimensional cylinder, where it reproduces the analytical Mie-theory solution. We then consider a sectorally perturbed cylinder with coupled azimuthal modes and demonstrate agreement with finite-element simulations. Finally, we combine the eigenvalue and scattering formulations for a material-programmed hard-wall annular metaatom and reproduce its scattering spectra and near fields. The developed framework provides a physically transparent modal approach to acoustic scattering by open resonators with reduced symmetry and spatially structured material parameters.

physics.comp-ph↗

arXiv2026

Optical Control of Chirality by Ultrafast Symmetry Breaking in Membrane Metasurfaces

Chirality underpins a wide range of light-matter interactions, yet methods for its dynamic control in photonic systems remain limited. Here, we demonstrate ultrafast all-optical control of chirality in silicon metasurfaces through transient symmetry breaking. Our approach exploits photonic eigenstates of opposite spatial parity engineered to be highly susceptible to symmetry perturbations. Optical excitation generates free carriers that establish a transient refractive-index gradient across the membrane thickness, breaking out-of-plane mirror symmetry and facilitating hybridization of the parity-opposite modes into chiral photonic states. This enables the reversible creation and modulation of chirality on a 10-100 ps timescale, manifested by pronounced changes in the metasurface circular dichroism. By dynamically reconfiguring a fundamental symmetry property of the photonic structure rather than merely its optical response, our work establishes a route towards ultrafast control of chiral light-matter interactions and opens opportunities for active nanophotonic and information processing technologies.

physics.optics↗

arXiv2026

Dark Optical Trapping of Resonant Transition-Metal Dichalcogenide Particles

Mitigating recoil events and minimizing optically induced heating are central challenges in the precise control and cooling of macroscopic particles. To overcome this, we propose trapping resonant dielectric particles for applications in ultra-high vacuum (UHV) levitodynamics. Contrary to other approaches, where suppressing the parasitic resonant scattering was achieved in a standing wave geometry, here we propose a single beam geometry in a dark trap regime. As a promising material platform, we focus on a class of transition-metal dichalcogenide (TMD) particles with high polarizability, characterized by refractive indices in the range $3.7$-$4.8$ and densities up to $9.3~\mathrm{g\,cm^{-3}}$. Using full Mie theory, we identify a range of TMD particle radii that support stable axial and radial magnetic quadrupole trapping in a bottle-beam configuration. We predict that for WS$_2$ particles with a mass of $0.5 \times 10^{12}\,\mathrm{amu}$, one can expect suppression of the scattering rate relative to the mechanical frequency down to $Γ/Ω\simeq 0.02$. This corresponds to a coherence time extended by approximately three orders of magnitude compared with silica particles of the same mass trapped in conventional bright optical traps at UHV. Combined with significantly reduced internal heating, remaining well below the melting point of the material, dark trapping of resonant TMD macroscopic particles emerges as a promising platform for exploring quantum physics with large masses.

physics.optics↗

arXiv2026

Unidirectional Transverse Scattering in Acoustic Dimers

We study unidirectional transverse scattering in a two-dimensional acoustic dimer composed of two circular subwavelength scatterers. Using a coupled multipole model, we show that interparticle coupling enables effective monopole--dipole interference and supports a transverse Kerker effect under plane-wave excitation. In contrast to a single non-absorbing rotationally symmetric particle, where Kerker-type directional scattering is only approached in the weak-scattering limit, the dimer can combine pronounced directionality with strong overall scattering. This regime is promising for compact acoustic beam steering and directional wave routing.

physics.class-ph↗

arXiv2026

Spin-wave hybridization in bismuth iron garnet Mie spheres induced by the inverse Faraday effect

We show that the inverse Faraday effect can be used to engineer dipole--exchange spin-wave spectra in ferrimagnetic bismuth iron garnet (BIG) Mie spheres. Internal optical Mie resonances generate spatially structured effective magnetic fields whose symmetry is inherited from the optical near field and which act as controllable perturbations of the magnon Hamiltonian. For circularly polarized light incident collinearly with the equilibrium magnetization, the optical perturbation preserves axial symmetry while breaking mirror parity, thereby enabling hybridization of magnon modes with opposite parity within the same $\widehat{J}_z$ sector. Using coupled-mode theory, we derive the corresponding avoided-crossing spectrum and analytical expressions for the induced level splittings, which scale linearly with pump intensity. Numerical calculations for BIG spheres confirm the predicted hybridization and show that the splitting is maximized near optical Mie resonances, where field enhancement and magneto-optical response are strongest. We further discuss the roles of damping, linewidth, and heating, and show that the predicted MHz--hundreds-of-MHz splittings should be observable under realistic conditions. These results identify BIG Mie resonators as a promising platform for symmetry-selective optical control of spin-wave spectra.

cond-mat.mes-hall↗

arXiv2026

Optical Supertorque Induced by Mie-Resonant Modes

We introduce the concept of resonant optical torque that allows enhancing substantially a transfer of optical angular momentum (AM) of light to a subwavelength particle. We consider high-index cylindrical dielectric nanoparticles supporting Mie resonances, and explore a transfer of AM and how it is affected by absorption and particle shape. We analyze a simple trapping geometry of standing wave patterns created by opposite helical light waves. We uncover stable rotation of particles in both nodes and anti-nodes, and also study how specific particle properties influence the resonant optical torque. We demonstrate that adjusting particle asymmetry and losses can maximize spinning torque, and we predict "supertorque" originating from the scattering channel mixing. Our study offers a deeper understanding of the physics of resonant optical torque and its importance in manipulating AM transfer in optical systems, with promising implications for various fields and inspiring further research in resonant light-matter interactions.

physics.optics↗

arXiv2026

Directional Scattering-Induced Optical Forces on a Mie Particle near a Metal Interface

Optical manipulation of Mie-resonant dielectric nanoparticles is strongly influenced by their enhanced scattering and multipolar response, which fundamentally modifiesthe balance of optical forces. In this work, we study the optical forces acting on a resonant dielectric nanoparticle placed near a metal interface, where scattering occurs into both free-space and surface plasmon-polariton (SPP) channels. We show that the interference of electric and magnetic dipole moments leads to highly directional scattering in these channels, and the direction and magnitude of the scattering-induced force are directly linked to the angular directivity of the corresponding radiation channels. We show that in a cross-beam configuration, where the radiation-pressure contribution is suppressed, the optical force can be changed for almost 2π in a wide range of particle sizes that provides a route toward optical sorting of resonant nanoparticles.

physics.optics↗

arXiv2026

Dipole-exchange spin waves and mode hybridization in magnetic nanoparticles

We investigate spin-wave modes in confined ferromagnetic resonators with spherical and cylindrical geometries across the exchange-dominated, dipole-exchange, and dipolar interaction regimes. Starting from the linearized Landau-Lifshitz-Gilbert equation, we show that the projection of the total angular momentum and mirror parity are conserved quantities in the problem of axially symmetric resonators. These symmetries provide a natural classification of spin-wave modes and explain the degeneracy of exchange modes, as well as its lifting by dipolar interactions. Numerical analysis shows that the nonlocal dipolar interaction removes the exchange degeneracy and hybridizes modes, leading to avoided crossings between modes that belong to the same symmetry sector. To describe this behavior, we develop a coupled-mode theory formulated directly in terms of dynamical magnetization, which reduces the dipole-exchange problem to a finite system of interacting modes. The resulting framework provides a unified description of spin-wave spectra in confined magnetic particles from the exchange limit to the dipolar regime.

cond-mat.mes-hall↗

arXiv2025

Experimental Investigation of Acoustic Kerker Effect in Labyrinthine Resonators

Controlling the directionality of the acoustic scattering with single acoustic metaatoms has a key importance for reaching spatial routing of sound with acoustic metamaterials. In this paper, we present the experimental demonstration of the acoustic analogue of the Kerker effect realized in a two-dimensional coiled-space metaatom. By engineering the interference between monopolar and dipolar resonances within a high-index acoustic metaatom, we achieve directional scattering with suppressed backward or forward response at the first and second Kerker conditions respectively. Experimental measurements of the scattered pressure field, in a parallel-plate waveguide environment, show good agreement with the full-wave simulations. Our results validate the feasibility of Kerker-inspired wave control in acoustic systems and open new opportunities for directional sound manipulation.

physics.app-ph↗

arXiv2025

Mid-IR Light Modulators Enabled by Dynamically Tunable Ultra High-Q Silicon Membrane Metasurfaces

Metasurfaces have emerged as a powerful platform to control free-space light at the subwavelength scale, enabling applications in sensing, lasing, nonlinear optics, and quantum photonics. However, their practical deployment is hindered by two key limitations: a tradeoff between low-Q resonances and weak amplitude contrast, and their predominantly static nature allowing only passive functionalities. These challenges are further aggravated in the application-relevant mid-infrared (mid-IR) range, where the lack of suitable low-loss materials and the strong absorption of common substrates such as silicon oxide or sapphire severely constrain performance and scalability. Here, we address these issues with actively tunable single-crystalline silicon membrane metasurfaces that combine high-Q resonances, strong amplitude contrast, and wafer-scale fabrication compatible dimensions for high throughput manufacturing. Our platform achieves record-high measured Q-factors up to 3000 in the mid-IR spectrum, supporting efficient dynamic modulation through two distinct schemes: (i) on-chip electro-thermal tuning via Joule heating, sustaining 50% modulation depth at CMOS-compatible voltages and speeds up to 14.5 kHz, and (ii) ultrafast all-optical modulation via carrier generation in silicon, reaching nanosecond response times and estimated sub-GHz modulation rates. By uniting sharp resonances, strong contrast, large-scale manufacturability, and dynamic tunability, our active silicon membrane metasurfaces advance the frontier of mid-IR nanophotonics and open new opportunities in sensing, free-space communication, thermal radiation management, and quantum technologies.

physics.optics↗

arXiv2025

Optical Spintronics: Towards Optical Communication Without Energy Transfer

Energy, momentum, and angular momentum are fundamental properties tied to the symmetries of space and time, with photons and other elementary particles acting as carriers of these quantities. In most optical and optoelectronic devices, energy transfer is crucial, but it often results in undesirable energy absorption. Moreover, non-reciprocal elements such as optical diodes and circulators are difficult to implement in photonics, as they typically require time-dependent perturbations, nonlinear effects, or external magnetic fields. This presents a significant barrier to the development of efficient, compact photonic technologies. We introduce the concept of optical spin current, wherein spin angular momentum is transferred by an electromagnetic field without accompanying energy transfer. This phenomenon is analogous to electron spin currents, where spin is decoupled from charge flow. Building on this principle, we propose optical spin diode and circulator -- devices that enable unidirectional propagation of spin currents while maintaining bidirectional energy flow, thus preserving reciprocity. Furthermore, we demonstrate asymmetric spin transfer between quantum dots mediated by the optical spin diode, highlighting the potential for novel optical spintronic functionalities. These findings lay the foundation for devices that leverage optical spin transfer, opening new avenues for advancements in optical spintronics.

physics.optics↗

arXiv2024

Light structuring via nonlinear total angular momentum addition with flat optics

Shaping the structure of light with flat optical devices has driven significant advancements in our fundamental understanding of light and light-matter interactions, and enabled a broad range of applications, from image processing and microscopy to optical communication, quantum information processing, and the manipulation of microparticles. Yet, pushing the boundaries of structured light beyond the linear optical regime remains an open challenge. Nonlinear optical interactions, such as wave mixing in nonlinear flat optics, offer a powerful platform to unlock new degrees of freedom and functionalities for generating and detecting structured light. In this study, we experimentally demonstrate the non-trivial structuring of third-harmonic light enabled by the addition of total angular momentum projection in a nonlinear, isotropic flat optics element -- a single thin film of amorphous silicon. We identify the total angular momentum projection and helicity as the most critical properties for analyzing the experimental results. The theoretical model we propose, supported by numerical simulations, offers quantitative predictions for light structuring through nonlinear wave mixing under various pumping conditions, including vectorial and non-paraxial pump light. Notably, we reveal that the shape of third-harmonic light is highly sensitive to the polarization state of the pump. Our findings demonstrate that harnessing the addition of total angular momentum projection in nonlinear wave mixing can be a powerful strategy for generating and detecting precisely controlled structured light.

physics.optics↗

arXiv2024

Excitation of surface plasmon-polaritons through optically-induced ultrafast transient gratings

Ultrafast excitation of non-equilibrium carriers under intense pulses offer unique opportunities for controlling optical properties of semiconductor materials. In this work, we propose a scheme for ultrafast generation of surface plasmon polaritons (SPPs) via a transient metagrating formed under two interfering optical pump pulses in the semiconductor GaAs thin film. The grating can be formed due to modulation of the refractive index associated with the non-equilibrium carriers generation. The formed temporal grating structure enables generation of SPP waves at GaAs/Ag interface via weak probe pulse excitation. We propose a theoretical model describing non-equilibrium carriers formation and diffusion and their contribution to permittivity modulation via Drude and band-filling mechanisms. We predict that by tuning the parameters of the pump and probe one can reach critical coupling regime and achieve efficient generation of SPP at the times scales of 0.1-1 ps.

physics.optics↗

arXiv2024

Acoustic forces near elastic substrate

In this work, we study the acoustic forces acting on particles due to sound scattering at the interface with an elastic substrate. Utilizing the Green's function formalism, we predict that excitation of leaking Rayleigh wave results in strong modification of the acoustic pressure force acting on a monopole scatterer and changes the equilibrium position of particles above the substrate surface. We also showed that the presence of a substrate changes the configuration of the acoustical binding of two particles due to multiple rescattering of acoustic wave from the interface. The reported results propose the method of acoustic manipulation via surface waves excitation and demonstrate the effect from elastic media in acoustical trapping of microobjects.

physics.class-ph↗

arXiv2024

Acoustic Lateral Recoil Force and Stable Lift of Anisotropic Particles

Acoustic forces and torques are of immense importance for manipulation of particles, in particular in biomedical applications. While such forces and torques are well understood for small spherical particles with lowest-order monopole and dipole responses, the higher-order effects for larger anisotropic particles have not been properly investigated. Here we examine the acoustic force and torque on an anisotropic (spheroid) particle and reveal two novel phenomena. First, we describe the lateral recoil force, orthogonal to the direction of the incident wave and determined by the tilted orientation of the particle. Second, we find conditions for the stable acoustic lift, where the balanced torque and force produce a stable lateral drift of the tilted particle. We argue that these phenomena can bring about new functionalities in acoustic manipulation and sorting of anisotropic particles including biological objects such as blood cells.

physics.class-ph↗