arXiv subjects

D. Solovyev

Publications and source records attributed to D. Solovyev.

At least 19 recordsLinked to original sources

arXiv2026

Long-range magnetic interaction within quantum electrodynamics formalism

Within the framework of quantum electrodynamics, the interaction between two atoms at large distances is analyzed. Using the S-matrix formalism, an expression for the magnetic interaction potential is derived, which agrees with the well-known result of classical electrodynamics. However, quantum electrodynamics goes beyond this conventional result and allows one to treat a wide range of problems related to the structure of atomic energy levels. In particular, it is shown that the asymptotic behavior of the interaction potential can deviate from the classical prediction, depending on the atomic states involved. As an example, dispersion coefficients are calculated for the s-states of hydrogen atoms, where the long-range potential reduces to a spin-spin interaction. The results obtained open up the possibility of a straightforward comparative analysis of long-range interaction potentials between atoms of matter and antimatter. The applicability of this approach is demonstrated for the hydrogen-antihydrogen system.

physics.atom-ph↗

arXiv2026

Reassessment of line profile asymmetry in measurements of the 1s-2s energy interval in hydrogen

Experiments to determine transition frequencies in the hydrogen atom represent some of the most precise spectroscopic measurements and are at a higher level among simple atomic systems. The most persistent measured value in hydrogen is the energy interval corresponding to the $1s-2s$ two-photon transition. The achieved experimental precision is several parts of $10^{-15}$ and has not changed over the last two decades. Although repeated experiments in 2011 and 2013 have improved the accuracy by several times, the frequency value has not changed significantly. On this basis, the frequency of the $1s-2s$ transition holds pivotal for determining physical quantities such as the Rydberg constant and the proton charge radius. Theoretical efforts to study in detail the effects that might influence such precise measurements have not revealed significant contributions. The present work revises the theoretical analysis of the line contour asymmetry and its influence on the determination of the two-photon absorption transition frequency, taking into account the theoretical achievements of recent years in this direction. It is shown that the asymmetry of the observed profile can lead to a $1s-2s$ transition frequency shift at the level of modern experimental accuracy. The found frequency shift is consistent with the line shape model contribution that forms the error budget of the experimental measurements. Adjustment can be carried out on the basis of the asymmetric profile that has become standard in recent years.

physics.atom-ph↗

arXiv2026

Non-adiabatic Effects Induced by Strong Light-Matter Coupling in Cavity QED

We present a systematic study of the diagonal Born-Oppenheimer correction (DBOC) for atoms and molecules embedded in optical cavities and interacting with a quantized electromagnetic field. By explicitly evaluating the nuclear kinetic energy operator, we analyze cavity-induced modifications of DBOC within a quantum electrodynamics configuration-interaction (QED-CI) framework built on quantum electrodynamics Hartree-Fock (QED-HF) and strong-coupling quantum electrodynamics Hartree-Fock (SC-QED-HF) reference states. The analysis covers a diverse set of atomic and molecular systems, including He, H-, Be, H2, LiH, HF, ammonia (NH3), and formaldehyde (CH2O). We show that the presence of the cavity leads to shifts in molecular dissociation energies on the order of a few inverse centimeters. For several atomic systems, the inclusion of the DBOC yields a pronounced effect, with the correction magnitude reaching the experimental resolution. These findings reveal finite nuclear mass effects as an essential component of nuclear dynamics in cavity QED and suggest their relevance for precision analysis in strongly coupled light-matter systems.

physics.atom-ph↗

arXiv2025

Multipole decomposition of the thermal one-loop self-energy correction for a bound atomic electron

In this paper, we present a comprehensive analysis of the one-loop self-energy correction at finite temperature for the bound electron. In this approach, we study the influence of thermal radiation on atomic systems. Along the way, we found well-known effects, including thermal Stark and Zeeman shifts, as well as thermal quadrupole interactions and relativistic corrections to the multipole expansion of photon field operators. We show that the corresponding contributions arise from the decomposition of the fully relativistic expression in terms of the $\alpha Z$ parameter. The presented analysis unambiguously determines the consistency of the quantum electrodynamics theory at finite temperature (TQED) with the perturbation theory of quantum mechanics (QM). Although our analysis mainly focuses on the hydrogen atom model, their potential implications for precision spectroscopic experiments are discussed.

physics.atom-ph↗

arXiv2025

Exploring the Properties of Light Diatomic Molecules in Strong Magnetic Fields

In this study, we develop and implement a specialized coupled-cluster (CC) approach tailored for accurately describing atoms and molecules in strong magnetic fields. Using the open-source Ghent Quantum Chemistry Package (\texttt{GQCP}) in conjunction with the Python-based Simulations of Chemistry Framework (\texttt{PySCF}), we calculate potential energy curves, permanent and transient dipole moments, as well as vibrational spectra for the diatomic molecules H$_2$, HeH$^+$ and LiH under various magnetic field strengths adopting a fully non-perturbative treatment. The main computational difficulties stem from the inclusion of the magnetic field in the Hamiltonian, in particular, from the presence of the angular momentum operator, which leads to a complication of the wave function and introduces a gauge-origin dependence. Addressing these challenges requires advanced modifications to existing routines, which we achieve by implementing gauge-comprising atomic orbitals (GIAOs) by using \texttt{GQCP}, and the capabilities offered by \texttt{PySCF}. This approach enhances the accuracy and reliability of the CC theory, opening pathways for more comprehensive investigations in molecular quantum chemistry at strong magnetic fields.

physics.atom-ph↗

arXiv2024

The blackbody radiation vibrational level shifts in the ground electronic state of N$_{2}^{+}$

Homonuclear molecules have emerged as a crucial component in the pursuit of frequency standards, offering a promising avenue for the discovery of new physics phenomena that transcend the standard model. They also provide a unique approach to constraining variations in fundamental constants over time, thereby complementing the capabilities of atomic clocks. A notable challenge faced by molecular and single atomic quantum systems is the management of blackbody radiation (BBR), which introduces significant systematic errors and is challenging to regulate effectively. To address this issue, we perform {\it ab-initio} quantum chemical calculations to accurately determine the potential energy curve and the polarizability tensor for the ground state of the N$_2^+$ molecular ion, one of the most promising candidates for searching for variation of $m_{e}/m_{p}$ and creating frequency standards. We then calculate the BBR shifts affecting the vibrational levels of the ground electronic X$^2\Sigma_g^+$ state, marking a substantial contribution towards the precise experimental measurements.

physics.atom-ph↗

arXiv2024

Effect of antiprotons on hydrogen-like ions in external magnetic fields

In the present work, quasi-molecular compounds consisting of one antiproton ($\bar{p}$) and one hydrogen-like ion are investigated: $\mathrm{He}^{+} - \bar{p}$, $\mathrm{Li}^{2+} - \bar{p}$, $\mathrm{C}^{5+} - \bar{p}$, $\mathrm{S}^{15+} - \bar{p}$, $\mathrm{Kr}^{35+} - \bar{p}$, $\mathrm{Ho}^{66+} - \bar{p}$, $\mathrm{Re}^{74+} - \bar{p}$, $\mathrm{U}^{91+} - \bar{p}$. For the calculations, the Dirac equation with two-center potential is solved numerically using the dual-kinetically balanced finite-basis-set method adapted to systems with axial symmetry (A-DKB). Adiabatic potential curves are constructed for the ground state of the above quasi-molecular compounds in the framework of the A-DKB approach. Calculations were also performed for the case of an external magnetic field (the field is taken into account non-perturbatively). Zeeman shifts of the quasi-molecular terms are obtained for a homogeneous magnetic field with a strength of the laboratory order (up to 100 Tesla) directed along the axis of the molecule.

physics.atom-ph↗

arXiv2024

Handling the asymmetric spectral line profile

This paper discusses some features of the spectral line profile theory used in the treatment of measured atomic transitions. It is shown that going beyond the established linear approximation for the spectral line contour in the case of its nonresonant extension, the potential for a more accurate extraction of atomic characteristics from experimental data arises. Using the example of the Lyman-$\alpha$ (Ly$_\alpha$) transition in hydrogen, a simple analysis of the observed spectral line distorted by a possible interfering transitions is given. In particular, the results obtained in the present work clearly demonstrate that the processing of the same experimental data at different settings can provide an accurate determination of the transition frequency, the centre of gravity as well as the hyperfine splitting of the ground state in hydrogen-like atomic systems. The latter is especially important for setting up precision spectroscopic experiments on the antihydrogen atom.

physics.atom-ph↗

arXiv2023

Theoretical prerequisites for the upcoming generation of precision spectroscopic experiments

Modern resonant spectroscopic experiments to measure transition frequencies in atoms have reached a level where a meticulous description of all aspects of the processes under study has become obligatory. The precision achieved in the experiments of A. Beyer, et al., Science 358, 79 (2017), has led to the fact that the determination of the transition frequency based on measured data is significantly refined by theoretical treatment of the observed spectral line profile. As it was predicted theoretically, a great impact of effects arising beyond the resonance approximation was found experimentally. These findings marked the beginning of the upcoming epoch in the resonant atomic spectroscopy when many commonly understood ideas became invalid. For example, the atomic transition may be characterized by several different but equally acceptable frequencies. Furthermore, we show that the picture becomes even more complicated when the observed spectral line profile is "identified" with one of the processes - emission or absorption. Precise determination of the transition frequency requires a description of the absorption line profile inseparable from the emission process and vice versa. The theoretical aspects discussed in this work provide prerequisites for more accurate and yet simpler experiments than those reported in Science 358, 79 (2017). Implementing the new physics expected in atomic resonance spectroscopy in the near future beyond the resonance approximation is unfeasible without resolving these issues.

physics.atom-ph↗

arXiv2023

Long-range interaction of hydrogen atoms at finite temperatures

In this study, we reexamine the long-range interaction between two atoms placed in an equilibrium thermal radiation environment. Employing the formalism of quantum electrodynamics at finite temperatures, we derive an expression for the thermal correction to the interaction potential and explore various asymptotic behaviors. The numerical calculations of temperature-dependent dispersion coefficients for both the ground and highly excited states of the hydrogen atom are performed. We proceed from the first principles of the theory to derive the dipole-dipole interaction at finite temperature. The analysis presented in this work reveals that the expressions established earlier in the context of phenomenological extrapolation from zero- to finite-temperature scenarios exhibit disparate asymptotic behavior and lead to overestimated results to those of the rigorous quantum electrodynamics approach.

physics.atom-ph↗

arXiv2023

Light one-electron quasi-molecular ions within the finite-basis-set method for the two-center Dirac equation

The electronic spectra of light one-electron quasi-molecular compounds H-H$^+$, He$^+$-He$^2+$ and He$^+$-H$^+$ are analyzed. To this end, the two-center Dirac equation is solved by the dual-kinetically balanced finite-basis-set method for axially symmetric systems termed as A-DKB. This method allows a complete relativistic consideration of these systems at fixed internuclear distances. A comparison of the obtained results with the nonrelativistic and relativistic calculations presented in the literature is performed. The advantages and disadvantages of the approach are discussed in details.

physics.atom-ph↗

arXiv2023

Combined two-loop self-energy corrections at finite and zero temperatures

In this paper we investigate higher-order corrections to the energies of bound states in hydrogen subjected to the external blackbody radiation field. In particular, within the framework of thermal quantum electrodynamics and $S$-matrix approach we analyze combined type of two-loop self-energy corrections, including one zero-vacuum and one loop at finite temperature. By utilizing the method of dimensional regularization, we derive closed analytical expressions for the energy shifts of atomic levels. Our numerical calculations demonstrate that even at room temperature these corrections can be significant for excited states, reaching the magnitude of the thermal induced Stark contribution.

physics.atom-ph↗

arXiv2022

Thermal contribution to measured $g$-factors in alkali-like atoms

In this paper, we consider a one-loop thermal correction to the $g$-factors of the ground and low-lying excited states in neutral alkaline-like atomic systems. As an example, we carried out calculations for Rb and Cs atoms, where optical measurements of transition frequencies set the metrological level of accuracy. With the development of atomic systems as the most accurate tool for spectroscopic experiments, it has become increasingly important to improve the accuracy of measuring the electron $g$-factor, which is currently at ~$10^{-12}$. The rapid progress in this field in recent years requires analysis not only of various relativistic, QED and other effects, but also theoretical studies of phenomena stimulated by the external thermal environment. We can expect that the thermal contribution to the $g$-factor calculated in our work may be of interest in the near future.

physics.atom-ph↗

arXiv2022

Natural line profile asymmetry

The paper discusses the line profile asymmetry of the photon scattering process that arises naturally in quantum electrodynamics (QED). Based on precision spectroscopic experiments conducted on hydrogen atoms, we focus our attention on the two-photon $1s-2s$ transition. As one of the most precisely determined transition frequencies, it is a key pillar of optical frequency standards and is used in determining fundamental physical constants, testing physical principles, and searching constraints on new fundamental interactions. The results obtained in this work show the need to take into account the natural line profile asymmetry in precision spectroscopic experiments.

physics.atom-ph↗

arXiv2022

Thermal radiative corrections to hyperfine structure of light hydrogen-like systems

In this work, we consider the thermal correction to the hyperfine interaction in hydrogen, deuterium, and the $^3$He$^+$ ion. This correction is effectively described by one-loop Feynman graphs in the framework of the quantum electrodynamics theory for bound states at a finite temperature. A simple analysis shows the importance of the obtained results for future prospects for measuring hyperfine splitting. In addition, the application for testing the time variation of fundamental constants is briefly discussed.

physics.atom-ph↗

arXiv2022

Radiative corrections to the level width in the presence of magnetic field

We study the influence of constant magnetic field combined with a field induced by the external thermal environment on the atomic decay rates. The importance of radiative corrections, including magnetic interaction, is demonstrated for hydrogen and hydrogen-like ions with low nuclear charge values $Z$. Based on the quantum electrodynamics description, the principal possibility of determining the $g$-factor by observing fluorescence is shown. The considered effects can be used in precision spectroscopic experiments and astrophysical studies.

physics.atom-ph↗

arXiv2022

Alternative interpretation of relativistic time-reversal and the time arrow

It is well-known that the 4-rotation in the 4-dimensional space-time is equivalent to the CPT-transformation (C is the charge conjugation, P is the space inversion and T is the time-reversal). The standard definition of the T-reversal includes the change of the sign of time variable and replacement of the initial state of the particle (system of particles) by the final state and vice versa. Since the time-reversal operation changes the state of a particle, the particle's wave function cannot be the eigenfunction of the corresponding operator with a certain eigenvalue, as in the case of space parity. Unlike the CPT-transformation, the separate P, T, or C transformations cannot be reduced to any 4-rotation. The extended Lorentz group incorporates all the separate C, P, or T transformations which do not bring the time axis out of the corresponding light cone. The latter restriction is included in the standard definition of the time-reversal. In the present communication, we ignore this restriction. This allows to introduce the "time arrow" operator and characterize every particle by the new quantum number - "time arrow" value. The wave functions of all particles are eigenfunctions of this operator with eigenvalues equal to "time arrow" values. The particles with the "time arrow" values opposite to the "time arrow" value in our universe form another universe (anti-universe). The existence of anti-universe can be confirmed, in principle, by laboratory (atomic) experiments. The anti-universe may be also considered as a candidate to the role of dark matter.

physics.gen-ph↗

arXiv2022

Line Profile Asymmetry in Precision Spectroscopy

In this review, we have investigated the asymmetry of the line profile in precision one- and two-photon spectroscopy of hydrogen and helium atoms within the framework of a rigorous QED approach. A detailed analysis of the angular correlations of the quantum interference effect has been carried out using various examples. Nonresonant effects are also considered in relation to some astrophysical problems. In particular, a rigorous QED derivation of the nonresonant extension for the Lorentz line profile is given using the Ly$_{\alpha}$ transition as an example; such a QED derivation has been lacking in the literature.

physics.atom-ph↗