arXiv subjects

I. Pavlov

Publications and source records attributed to I. Pavlov.

9 recordsLinked to original sources

arXiv2026

Interaction of twisted light with free twisted atoms

We investigate absorption and scattering of structured light by atoms, treating the photon and the atomic center of mass as spatially localized wave packets. We show that vortex photons can transfer orbital angular momentum (OAM) to the atomic center of mass with near-perfect efficiency in head-on collisions when the impact parameter $b$ is smaller than the atomic transverse coherence length $\sigma$, which ranges from nanometers to sub-micrometer scales. Larger offsets result in a shifted mean OAM and a finite variance, both controlled by the ratio $b/\sigma$. The wave-packet nature of light enables electronic transitions that violate standard selection rules, albeit with a clear hierarchy where the dipole transition dominates. For femtosecond pulses, the finite spatial coherence of the photon leads to measurable shaping of the resonant absorption lines. We demonstrate a transverse recoil of the atom in a vicinity of the photonic vortex, dubbed "the superkick", and its dual effect - "the selfkick" - when an initially twisted atomic packet experiences recoil upon absorbing a gaussian photon. These phenomena are within reach of experimental capabilities using structured light in combination with cold atomic beams and ions in Penning traps, providing a route to the controlled generation and manipulation of non-gaussian atomic packets.

quant-ph↗

arXiv2025

Angular momentum dynamics of vortex particles in accelerators

While conventional experiments typically employ plane-wave states of particles with definite momenta, vortex states represent cylindrical waves carrying an orbital angular momentum (OAM) projection along the propagation direction. This projection can be arbitrarily large, granting charged particles magnetic moments orders of magnitude greater than those of plane-wave states. Consequently, vortex beams could complement or replace spin-polarized beams in high-energy collisions, accessing observables beyond the reach of conventional experiments. We investigate the radiative and non-radiative OAM dynamics for relativistic vortex particles in accelerators. Our results show that the timescale for OAM loss via photon emission significantly exceeds typical acceleration times. Non-radiative OAM dynamics is governed by precession at a frequency distinct from that of spin. Similar to spin tunes, this induces resonances that can disrupt OAM at much lower energies than for spin-polarized beams. Thus, we propose using linacs for acceleration of the vortex beams, while Siberian snakes can be adapted for OAM manipulations.

physics.acc-ph↗

arXiv2024

Angular momentum effects in neutron decay

We investigate the intriguing phenomenon of beta decay of a free neutron in a non-plane-wave(structured) state. Our analysis covers three types of states: unpolarized vortex (Bessel) neutrons that possess nonzero orbital angular momentum (OAM), Laguerre-Gaussian wave packets, and spin-correlated OAM (spin-orbit) states characterized by unique polarization patterns. These states are of particular interest as they have recently been generated in neutron optics experiments and have promising applications in studies of quantum magnetic materials. The spectral-angular distributions (SAD) of the emitted electrons and protons are examined. We show that the high sensitivity of the protons SAD to the structure of the neutron wave packet can be used as a tool to extract the distinctive features of the non-plane-wave neutron states. Furthermore, we demonstrate that the angular distribution of the emitted particles serves as a reflection of the spatial symmetries inherent to the neutron wave packet.

hep-ph↗

arXiv2023

Emission of twisted photons by a Dirac electron in a strong magnetic field

We study spontaneous emission of a photon during the transitions between relativistic Landau states of an electron in a constant magnetic field that can reach the Schwinger value of $H_c = 4.4 \times 10^9$ T. In contrast to the conventional method in which detection of both the final electron and the photon is implied in a certain basis, here we derive the photon state as it evolves from the process itself. It is shown that the emitted photon state represents a twisted Bessel beam propagating along the field axis with a total angular momentum (TAM) projection onto this axis $\ell-\ell'$ where $\ell$ and $\ell'$ are the TAM of the initial electron and of the final one, respectively. Thus, the majority of the emitted photons turn out to be twisted with $\ell-\ell' \gtrsim 1$, even when the magnetic field reaches the critical value of $H\sim H_c$. The transitions without a change of the electron angular momentum, $\ell'=\ell$, are possible, yet much less probable. We also compare our findings with those for a spinless charged particle and demonstrate their good agreement for the transitions without change of the electron spin projection even in the critical fields, while the spin-flip transitions are generally suppressed. In addition, we argue that whereas the ambiguous choice of an electron spin operator affects the differential probability of emission, this problem can partially be circumvented for the photon evolved state because it is the electron TAM rather than the spin alone that defines the TAM of the emitted twisted photon.

hep-ph↗

arXiv2022

Elastic scattering of Airy electron packets on atoms

The problem of elastic scattering of electron Airy beams on potential fields is considered for a hydrogen atom in the ground state and for Yukawa potential. It is demonstrated that the angular dependence of the scattering probability density is in general azimuthally asymmetric. When the position of the atom happens to coincide with one the minima of the probability density of the Airy beam the asymmetric pattern is represented by four separated peaks. We show that this behaviour is very sensitive to the precision with which the relative position of the atom and the minima is defined and study how uncertainty in the position measured in terms of the transverse size of the wave-packet affects observation of azimuthal asymmetry. Finally, we consider a spatially localized target and discuss the difficulties of observing the azimuthal asymmetry for targets with sizes that exceed the critical value determined by the beam parameters and the position of the target center.

quant-ph↗

arXiv2020

Azimuthal and polar anchoring energies of aligning layers structured by nonlinear laser lithography

In spite of the fact that there are different techniques in the creation of the high-quality liquid crystals (LCs) alignment by means of various surfaces, the azimuthal and polar anchoring energies as well as the pre-tilt angle are important parameters to all of them. Here, the modified by a certain manner aligning layers, previously formed by nonlinear laser lithography (NLL), having high-quality nano-periodic grooves on Ti surfaces, recently proposed for LC alignment was studied. The change of the scanning speed of NLL in the process of nano-structured Ti surfaces and their further modification by means of ITO-coating, and deposition of polyimide film has enabled different aligning layers, whose main characteristics, namely azimuthal and polar anchoring energies, were measured. For the modified aligning layers, the dependencies of the twist and pre-tilt angles for LC cells filled by nematic E7 (Δε > 0) and MLC-6609 (Δε < 0) were obtained. Also the contact angle for droplets of isotropic liquid (glycerol), and nematic LCs was measured for the various values of the scanning speed during the laser processing.

physics.app-ph↗

arXiv2019

Demonstration of nonstoquastic Hamiltonian in coupled superconducting flux qubits

Quantum annealing (QA) is a heuristic algorithm for finding low-energy configurations of a system, with applications in optimization, machine learning, and quantum simulation. Up to now, all implementations of QA have been limited to qubits coupled via a single degree of freedom. This gives rise to a stoquastic Hamiltonian that has no sign problem in quantum Monte Carlo (QMC) simulations. In this paper, we report implementation and measurements of two superconducting flux qubits coupled via two canonically conjugate degrees of freedom (charge and flux) to achieve a nonstoquastic Hamiltonian. Such coupling can enhance performance of QA processors, extend the range of quantum simulations. We perform microwave spectroscopy to extract circuit parameters and show that the charge coupling manifests itself as a YY interaction in the computational basis. We observe destructive interference in quantum coherent oscillations between the computational basis states of the two-qubit system. Finally, we show that the extracted Hamiltonian is nonstoquastic over a wide range of parameters.

quant-ph↗

arXiv2017

The alignment of nematic liquid crystal by the Ti layer processed by nonlinear laser lithography

It is well known that the alignment of liquid crystals can be realized by rubbing or photoalignment technologies. Recently nonlinear laser lithography was introduced as a fast, relatively low-cost method for large area nano-grating fabrication based on laser-induced periodic surface structuring. In this letter for the first time the usage of the nonlinear laser lithography as a perspective method of the alignment of nematics was presented. By nonlinear laser lithography, microgrooves with about 1 μm period were formed on Ti layer. The microstructured Ti layer was coated with oxidianiline-polyimide film with annealing of the polymer followed without any further processing. Aligning properties of microstructured Ti layers were examined with combined twist LC cell. The dependencies of the twist angle of LC cells and azimuthal anchoring energy of layers on scanning speed and power of laser beam during processing of the Ti layer were the focus of our studies as well. The maximum azimuthal anchoring energy, obtained for pure microstructured Ti layer, is comparable with photoalignment technology. It was found that the deposition of polyimide film on microstructured Ti layer leads to the gain effect of the azimuthal anchoring energy. Also, AFM study of aligning surfaces was carried out.

cond-mat.soft↗

arXiv2017

In-chip microstructures and photonic devices fabricated by nonlinear laser lithography deep inside silicon

Silicon is an excellent material for microelectronics and integrated photonics with untapped potential for mid-IR optics. Despite broad recognition of the importance of the third dimension, current lithography methods do not allow fabrication of photonic devices and functional microelements directly inside silicon chips. Even relatively simple curved geometries cannot be realized with techniques like reactive ion etching. Embedded optical elements, like in glass, electronic devices and better electronic-photonic integration are lacking. Here, we demonstrate laser-based fabrication of complex 3D structures deep inside silicon using 1 micrometer-sized dots and rod-like structures of adjustable length as basic building blocks. The laser-modified Si has a different optical index than unmodified parts, which enables numerous photonic devices. Optionally, these parts are chemically etched to produce desired 3D shapes. We exemplify a plethora of subsurface, i.e., "in-chip" microstructures for microfluidic cooling of chips, vias, MEMS, photovoltaic applications and photonic devices that match or surpass the corresponding state-of-the-art device performances.

physics.optics↗