arXiv subjects

I. M. Tkachenko

Publications and source records attributed to I. M. Tkachenko.

13 recordsLinked to original sources

arXiv2025

Comment on 'Collectively enhanced quantum measurements at the Heisenberg limit'

In a seminal paper [8] it was shown that Heisenberg-limited measurements could be achieved without using entangled states by coupling the quantum resources to a common environment that could be measured, at least, in part. The authors also claimed that their method would be robust under decoherence, and, in particular, applied it to derive an analytical expression to measure the change in length of an optical cavity within the Tavis-Cummings model using the superradiance approximation, which would still have a 1/N scaling. Here, we show that the analytical derivations in [8] are incompatible with the cavity superradiance, leading to the standard quantum-limited scaling 1/\sqrt{N}.

quant-ph↗

arXiv2025

Modification of the uniform electron gas polarizational stopping power due to the interaction of the projectile with new collective modes at moderate and strong coupling

This paper presents a detailed study of the polarizational stopping power of a homogeneous electron gas in moderate and strong coupling regimes using the self-consistent version of the method of moments as the key theoretical approach capable of expressing the dynamic characteristics of the system in terms of the static ones, which are the moments. We develop a robust framework that relies on nine sum rules and other exact relationships to analyze electron-electron interactions and their impact on energy-loss processes. We derive an expression for the stopping power that takes into account both quantum statistical effects and electron correlation phenomena. Our results demonstrate significant deviations from classical stopping power predictions, especially under the strong coupling conditions when electron dynamics is highly dependent on collective behavior and a projectile interacts with the system collective modes revealed in Phys. Rev. B 107, 195143 (2023). This work not only advances the theoretical understanding of the homogeneous electron gas but also has implications for practical applications in fields such as plasma physics and materials science.

physics.plasm-ph↗

arXiv2023

Analysis of dynamical effects in the uniform electron liquids with the self-consistent method of moments complemented by the Shannon information entropy and the path-integral Monte-Carlo simulations

Dynamical properties of uniform electron fluids (jellium model) are studied within a novel non-perturbative approach consisting in the combination of the self-consistent version of the method of moments (SCMM) involving up to nine sum rules and other exact relations, the two-parameter Shannon information entropy maximization procedure, and the ab initio path integral Monte Carlo (PIMC) simulations of the imaginary-time intermediate scattering function. The explicit dependence of the electronic dynamic structure factor (DSF) on temperature and density is studied in a broad realm of variation of the dimensionless parameters ($2\leq r_s\leq 36$ and $1\leq θ\leq 8$). When the coupling is strong ($r_s\geq 16$) we clearly observe a bi-modal structure of the excitation spectrum with a lower-energy mode possessing a well pronounced roton-like feature ($θ\leq 2$) and an additional high-energy branch within the roton region which evolves into the strongly overdamped high-frequency shoulder when the coupling decreases ($r_s\leq 10$). We are not aware of any reconstruction of the DSF at these conditions with the effects of dynamical correlations, included here via the intermediate scattering and the dynamical Nevanlinna parameter functions. The standard static-local-field approach fails to reproduce this effect. The reliability of our method is confirmed by a detailed comparison with the recent ab initio dynamic-local-field approach by Dornheim et al. [Phys.Rev.Lett. 121, 255001 (2018)] available for high/moderate densities ($r_s\leq 10$). Moreover, within the SCMM we are able to construct the modes dispersion equation in a closed analytical form and find the decrements (lifetimes) of the quasiparticle excitations explicitly. The physical nature of the revealed modes is discussed. Mathematical details of the method are complemented in the Supplementary Material.

physics.comp-ph↗

arXiv2023

Dynamic properties and the roton mode attenuation in the liquid 3He: an ab initio study within the self-consistent method of moments

The dynamic structure factor and the eigenmodes of density fluctuations in the uniform liquid $^3$He are studied using a novel non-perturbative approach. This new version of the self-consistent method of moments invokes up to nine sum rules and other exact relations involving the spectral density, the two-parameter Shannon information entropy maximization procedure, and the ab initio path integral Monte Carlo (PIMC) simulations which provide crucial reliable input information on the system static properties. Detailed analysis of the dispersion relations of collective excitations, the modes decrements and the static structure factor (SSF) of $^3$He at the saturated vapor pressure is performed. The results are compared to available experimental data~[1,2]. The theory reveals a clear signature of the roton-like feature in the particle-hole segment of the excitation spectrum with a significant reduction of the roton decrement in the wavenumber range $1.3 A^{-1} \leq q\leq 2.2 A^{-1}$. The observed roton mode remains a well defined collective excitation even in the particle-hole band, where, however, it is strongly damped. Hence, the existence of the roton-like mode in the bulk liquid $^3$He is confirmed like in other strongly interacting quantum fluids~[3]. The phonon branch of the spectrum is also studied with a reasonable agreement with the same experimental data being achieved. The presented combined approach permits to produce ab initio data on the system dynamic characteristics in a wide range of physical parameters and for other physical systems.

physics.comp-ph↗

arXiv2013

The dynamic conductivity of strongly non-ideal plasmas: is the Drude model valid?

The method of moments is used to calculate the dynamic conductivity of strongly coupled fully ionized hydrogen plasmas. The electron density $n_{e}$ and temperature $T$ vary in the domains $ 10^{21} < n_{e} < 10^{24} {\rm cm}^{-3}$, $10^{4} {\rm K} < T < 10^{6} {\rm K}$. The results are compared to some theoretical data.

physics.plasm-ph↗

arXiv2010

Static and Dynamic Structure Factors with Account of the Ion Structure for High-temperature Alkali and Alkaline Earth Plasmas

The $e-e$, $e-i$, $i-i$ and charge-charge static structure factors are calculated for alkali and Be$^{2+}$ plasmas using the method described by Gregori et al. in \cite{bibGreg2006}. The dynamic structure factors for alkali plasmas are calculated using the method of moments \cite{bibAdam83}, \cite{bibAdam93}. In both methods the screened Hellmann-Gurskii-Krasko potential, obtained on the basis of Bogolyubov's method, has been used taking into account not only the quantum-mechanical effects but also the ion structure \cite{bib73}. PACS: 52.27.Aj (Alkali and alkaline earth plasmas, Static and dynamic structure factors), 52.25.Kn (Thermodynamics of plasmas), 52.38.Ph (X-ray scattering)

physics.plasm-ph↗

arXiv2008

Energy losses of fast heavy-ion projectiles in dense hydrogen plasmas

It has been recently shown that the Bethe-Larkin formula for the energy losses of fast heavy-ion projectiles in dense hydrogen plasmas is corrected by the electron-ion correlations [Phys. Rev. Lett. \textbf{101}, 075002 (2008)]. We report numerical estimates of this correction based on the values of $g_{ei}(0)$ obtained by numerical simulations in [Phys. Rev. E \textbf{61}, 3470 (2000)]. We also extend this result to the case of projectiles with dicluster charge distribution. We show that the experimental visibility of the electron-ion correlation correction is enhanced in the case of dicluster projectiles with randomly orientated charge centers. Although we consider here the hydrogen plasmas to make the effect physically more clear, the generalization to multispecies plasmas is straightforward.

physics.plasm-ph↗

arXiv2008

Fast projectile stopping power of quantal multi-component strongly coupled plasmas

The Bethe-Larkin formula for the fast projectile stopping power is extended to multi-component plasmas. The results are to contribute to the correct interpretation of the experimental data, which could permit to test the existing and future models of thermodynamic, static, and dynamic characteristics of strongly coupled Coulomb systems.

physics.plasm-ph↗

arXiv2007

Polarizational stopping power of heavy-ion diclusters in two-dimensional electron liquids

The in-plane polarizational stopping power of heavy-ion diclusters in a two-dimensional strongly coupled electron liquid is studied. Analytical expressions for the stopping power of both fast and slow projectiles are derived. To go beyond the random-phase approximation we make use of the inverse dielectric function obtained by means of the method of moments and some recent analytical expressions for the static local-field correction factor.

cond-mat.str-el↗

arXiv2007

Collective and static properties of model two-component plasmas

Classical MD data on the charge-charge dynamic structure factor of two-component plasmas (TCP) modeled in Phys. Rev. A 23, 2041 (1981) are analyzed using the sum rules and other exact relations. The convergent power moments of the imaginary part of the model system dielectric function are expressed in terms of its partial static structure factors, which are computed by the method of hypernetted chains using the Deutsch effective potential. High-frequency asymptotic behavior of the dielectric function is specified to include the effects of inverse bremsstrahlung. The agreement with the MD data is improved, and important statistical characteristics of the model TCP, such as the probability to find both electron and ion at one point, are determined.

physics.plasm-ph↗

arXiv2007

Fast projectile stopping power of two-dimensional strongly correlated electron liquids

We study the high-velocity-projectile limit of the polarizational contribution to the in-plane stopping power in a strongly coupled two-dimensional electron liquid. The dielectric formalism based on the method of moments is employed. The frequency moments of the loss function are calculated using the model Hamiltonian including the two-dimensional Coulomb interaction potential proportional to the inverse power of k. We prove that the leading term of the high-velocity asymptote, like in the random-phase approximation, is not affected by correlations.

cond-mat.str-el↗

arXiv2007

Reflectivity and Exact Asymptotic Forms of the Dielectric Function of Non-Ideal Plasmas

The problem of calculation of the reflectivity of non-ideal shock-compressed plasmas is revisited. The dielectric formalism based on the method of moments incorporating exact asymptotic forms and sum rules is applied to the new experimental data. The approach is based on the Ansatz of reflection of laser radiation from a thin shock-front and possesses one adjustable parameter which depends only on the thermodynamic conditions of the experiment. A self-consistent agreement with all available experimental data is achieved.

physics.plasm-ph↗

arXiv1999

Electromagnetic modes in cold magnetized strongly coupled plasmas

The spectrum of electromagnetic waves propagating in a strongly coupled magnetized fully ionized hydrogen plasma is found. The ion motion and damping being neglected, the influence of the Coulomb coupling on the electromagnetic spectrum is analyzed.

physics.plasm-ph↗