arXiv subjects

D. Karlovets

Publications and source records attributed to D. Karlovets.

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↗

arXiv2026

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↗

arXiv2025

Attosecond physics hidden in Cherenkov radiation

Cherenkov radiation of charged particles moving with superluminal velocities in transparent media is a well-studied phenomenon with a plethora of applications. Its microscopic origins can be traced to the polarization of atomic shells, characterized by time scales in the subfemtosecond range - dynamics that eludes conventional macroscopic treatment. Here we present a theoretical framework for probing the intrinsic dynamics of Cherenkov radiation, unveiling quantum features absent in classical realm and even in a fully quantum theory in momentum space. These features include a finite formation length and spreading time of the photon, the latter becoming negative nearby the Cherenkov angle, a finite flash duration tied to the size of the electron packet, along with a shift in the photon arrival time that can be either positive or negative and necessitates going beyond the far-field approximation. The calculated time scales lie in the attosecond range for the relevant parameters, thus linking this macroscopic phenomenon back to its atomic origins. Finally, we propose that by measuring the duration of the Cherenkov flash one can in principle retrieve the length of the emitting packet, deepening our understanding of quantum coherence effects in photon emission.

quant-ph↗

arXiv2025

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↗

arXiv2024

Elastic scattering of Laguerre-Gaussian electron packets on atoms

We explore elastic scattering of non-relativistic electrons in the form of standard Laguerre-Gaussian (sLG) and elegant Laguerre - Gaussian (eLG) packets on atomic targets in the generalized Born approximation and compare these results to the reference with Bessel-Gaussian (BG) packets. Scattering by hydrogen-like, iron, silver, and golden targets is considered. The incident electron carries a nonzero orbital angular momentum, while sLG and eLG packets have a definite radial quantum number n as well. In scattering of sLG and eLG wave packets by a macroscopic target sensitivity of the average cross section to the orbital angular momentum is observed, which is absent for BG packets. We highlight the opportunity to employ the differences in the experimental scattering results for the revelation of the properties of incident twisted electron wave packets

physics.atom-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↗

arXiv2023

Emission of twisted photons by a scalar charged particle in a strong magnetic field

We consider the emission of a photon by a scalar charged particle in a constant and uniform magnetic field. In contrast to the conventional approach with both photon and outgoing charge being assumed to be detected, we study the case where only the charge is detected and investigate the properties of the emitted photon. The background magnetic field is taken into account exactly in the calculations and the charge is described by relativistic Landau states. It is shown that the emitted photon state represents a twisted Bessel beam with a total angular momentum given by $\ell-\ell'$, where $\ell$ and $\ell'$ are angular momentum quantum numbers of the initial and final charged particle, respectively. The majority of photons emitted by unpolarized charges, especially in the hard X-ray and $γ$-ray range and in critical and sub-critical magnetic fields, as compared to the Schwinger value of $H_c = 4.4\times 10^9$ T, turn out to be twisted with $\ell-\ell'\gtrsim 1$.

hep-ph↗

arXiv2023

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↗

arXiv2021

The passage of a vortex electron over an inclined grating

We study Smith-Purcell radiation from a conducting grating generated by an inclined passage of a shaped electron wave packet with an electric quadrupole moment in the non-paraxial regime. Spreading of an asymmetric wave packet induces quadrupole corrections to the radiation field. Although the non-paraxial corrections stay small, they are dynamically enhanced during the interaction of the electron with the grating whose length exceeds the Rayleigh length of the packet. To simplify the possible experimental setup where such effects could be measured, we study the dependence of these effects on the inclination angle, i.e. the angle between the mean velocity of the packet and the surface of the grating. There is a minimal angle such that the multipole expansion always stays valid at the grating surface. In such a regime, the quadrupole contribution to the Smith-Purcell radiation can become the leading one, which represents a novel quantum effect impossible for classical point-like electrons. Thus, the impact of the wave-packet shape (vortex structure or non-spherical shape) can be observed experimentally by comparing the radiation for different orientations of the grating in the single-electron regime.

quant-ph↗