| 1. |
- Li, Wenxian, et al.
(författare)
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Multiconfiguration Dirac-Hartree-Fock calculations of Lande g-factors for ions of astrophysical interest : B II, C I-IV, Al I-II, Si I-IV, P II, S II, Cl III, Ar IV, Ca I, Ti II, Zr III, and Sn II
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 639
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Tidskriftsartikel (refereegranskat)abstract
- Aims. The Lande g-factor is an important parameter in astrophysical spectropolarimetry, used to characterize the response of a line to a given value of the magnetic field. The purpose of this paper is to present accurate Lande g-factors for states in B II, C I-IV, Al I-II, Si I-IV, P II, S II, Cl III, Ar IV, Ca I, Ti II, Zr III, and Sn II.Methods. The multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction methods, which are implemented in the general-purpose relativistic atomic structure package GRASP2K, are employed in the present work to compute the Lande g-factors for states in B II, C I-IV, Al I-II, Si I-IV, P II, S II, Cl III, Ar IV, Ca I, Ti II, Zr III, and Sn II. The accuracy of the wave functions for the states, and thus the accuracy of the resulting Lande g-factors, is evaluated by comparing the computed excitation energies and energy separations with the National Institute of Standards and Technology (NIST) recommended data.Results. All excitation energies are in very good agreement with the NIST values except for Ti II, which has an average difference of 1.06%. The average uncertainty of the energy separations is well below 1% except for the even states of Al I; odd states of Si I, Ca I, Ti II, Zr III; and even states of Sn II for which the relative differences range between 1% and 2%. Comparisons of the computed Lande g-factors are made with available NIST data and experimental values. Analysing the LS-composition of the wave functions, we quantify the departures from LS-coupling and summarize the states for which there is a difference of more than 10% between the computed Lande g-factor and the Lande g-factor in pure LS-coupling. Finally, we compare the computed Lande g-factors with values from the Kurucz database.
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| 2. |
- Nandi, Saikat, et al.
(författare)
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Generation of entanglement using a short-wavelength seeded free-electron laser
- 2024
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Ingår i: Science Advances. - 2375-2548. ; 10:16, s. 0668-0668
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Tidskriftsartikel (refereegranskat)abstract
- Quantum entanglement between the degrees of freedom encountered in the classical world is challenging to observe due to the surrounding environment. To elucidate this issue, we investigate the entanglement generated over ultrafast timescales in a bipartite quantum system comprising two massive particles: a free-moving photoelectron, which expands to a mesoscopic length scale, and a light-dressed atomic ion, which represents a hybrid state of light and matter. Although the photoelectron spectra are measured classically, the entanglement allows us to reveal information about the dressed-state dynamics of the ion and the femtosecond extreme ultraviolet pulses delivered by a seeded free-electron laser. The observed generation of entanglement is interpreted using the time-dependent von Neumann entropy. Our results unveil the potential for using short-wavelength coherent light pulses from free-electron lasers to generate entangled photoelectron and ion systems for studying spooky action at a distance.
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| 3. |
- Nandi, Saikat, et al.
(författare)
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Generation of entanglement using a short-wavelength seeded free-electron laser
- 2024
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Ingår i: SCIENCE ADVANCES. - 2375-2548. ; 10:16
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Tidskriftsartikel (refereegranskat)abstract
- Quantum entanglement between the degrees of freedom encountered in the classical world is challenging to observe due to the surrounding environment. To elucidate this issue, we investigate the entanglement generated over ultrafast timescales in a bipartite quantum system comprising two massive particles: a free-moving photoelectron, which expands to a mesoscopic length scale, and a light-dressed atomic ion, which represents a hybrid state of light and matter. Although the photoelectron spectra are measured classically, the entanglement allows us to reveal information about the dressed-state dynamics of the ion and the femtosecond extreme ultraviolet pulses delivered by a seeded free-electron laser. The observed generation of entanglement is interpreted using the time-dependent von Neumann entropy. Our results unveil the potential for using short-wavelength coherent light pulses from free-electron lasers to generate entangled photoelectron and ion systems for studying spooky action at a distance.
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| 4. |
- Papoulia, Asimina, et al.
(författare)
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Ab initio electronic factors of the A and B hyperfine structure constants for the 5s(2)5p6s( 1,3)P(1)(0) states in Sn I
- 2021
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society. - 2469-9926 .- 2469-9934. ; 103:2
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Tidskriftsartikel (refereegranskat)abstract
- Large-scale ab initio calculations of the electronic contribution to the electric quadrupole hyperfine constant B were performed for the 5s(2)5p6s( 1,3)P(1)(0)excited states of neutral tin. To probe the sensitivity of B to different electron correlation effects, three sets of variational multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction calculations employing different strategies were carried out. In addition, a fourth set of calculations was based on the configuration interaction Dirac-Fock-Sturm theory. For the 5s(2)5p6s( 1)P(1)(0) state, the final value of B/Q = 703(50) MHz/b differs by 0.4% from the one recently used by Yordanov et al. [Commun. Phys. 3, 107 (2020)] to extract the nuclear quadrupole moments Q for tin isotopes in the range Sn117-131 from collinear laser spectroscopy measurements. Efforts were made to provide a realistic theoretical uncertainty for the final B/Q value of the 5s(2)5p6s( 1)P(1)(0) state based on statistical principles and on correlation with the electronic contribution to the magnetic dipole hyperfine constant A.
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| 5. |
- Papoulia, Asimina, et al.
(författare)
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Ab initio electronic factors of the A and B hyperfine structure constants for the 5s25p6s1,3P01 states in Sn I
- 2021
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Ingår i: Physical Review A. - 2469-9926. ; 103:2
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Tidskriftsartikel (refereegranskat)abstract
- Large-scale ab initio calculations of the electronic contribution to the electric quadrupole hyperfine constant B were performed for the 5s25p6s1,3Po1 excited states of neutral tin. To probe the sensitivity of B to different electron correlation effects, three sets of variational multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction calculations employing different strategies were carried out. In addition, a fourth set of calculations was based on the configuration interaction Dirac-Fock-Sturm theory. For the 5s25p6s 1Po1 state, the final value of B/Q=703(50) MHz/b differs by 0.4% from the one recently used by Yordanov et al. [Commun. Phys. 3, 107 (2020)] to extract the nuclear quadrupole moments Q for tin isotopes in the range 117−131Sn from collinear laser spectroscopy measurements. Efforts were made to provide a realistic theoretical uncertainty for the final B/Q value of the 5s25p6s 1Po1 state based on statistical principles and on correlation with the electronic contribution to the magnetic dipole hyperfine constant A.
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| 6. |
- Papoulia, Asimina
(författare)
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Atomic Electrons as Sensitive Probes of Nuclear Properties and Astrophysical Plasma Environments : A Computational Approach
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with the relativistic modeling of atoms and ions. To interpret the stellar spectra and gain more insight from astrophysical observations, the underlying processes that generate the spectra need to be well understood and described. Examples of such processes are the interactions of atomic electrons with internal and external electromagnetic fields and with the nucleus.By exploring different computational methodologies, Paper I analyzes how the transition probabilities, of transitions involving high Rydberg states, depend on the gauge and the orbital set that is used in the calculations. Papers II and III contain large homogeneous data sets of parameters related to atomic radiative processes, namely transition energies, transition probabilities, weighted oscillator strengths, and lifetimes of excited states, for carbon and aluminium systems. These parameters are essential in astrophysical applications, e.g., in abundance and plasma analyses of stars. In addition, Paper IV presents extended data of Landé g-factors, used to characterize the response of spectral lines to a given value of an external magnetic field. The description of effects arising from the interplay between atomic electrons and nuclei, such as hyperfine structure splittings and isotope shifts, requires that the nuclear structure properties giving rise to these effects are well determined. This is, however, not always the case; as we move away from the valley of stability, data of nuclear structure observables are scarce. High-resolution measurements of hyperfine structures and isotope shifts, combined with first-principles atomic structure calculations, are commonly used to probe the structures of nuclei, including short-lived and radioactive systems. In Papers V and VI, measurements of the hyperfine structure in neutral tin were combined with atomic structure calculations to extract the electric quadrupole moments of tin isotopes. Paper VII presents a novel method that combines experimental isotope shifts and calculations of atomic parameters to probe details of nuclear charge density distributions, other than charge radii.
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| 7. |
- Papoulia, Asimina
(författare)
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Computational Atomic Structure: Applications to Astrophysics and Nuclear Structure
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with the modelling of atoms and ions. In heavy systems, where the effect of the nuclear size must be considered, a fully relativistic treatment based on the Dirac-Coulomb Hamiltonian is needed. Chapter two of the thesis provides an introduction to the basic principles of the fully relativistic multiconfiguration Dirac-Hartree-Fock (MCDHF) method, which is a variational approach for determining the wave functions. After we demonstrate how to obtain the best approximation of the wave functions by optimizing the energy expression, we describe how to compute the eigenvalues of operators other than the Hamiltonian, and how these eigenvalues correspond to measurable quantities. Chapter three and four, respectively, summarize the work done in the two published papers, illustrating some of the applications of the relativistic atomic structure theory.Paper I is an example of atomic structure calculations for astrophysical applications. Extensive amount of atomic transition data are produced for the systems of neutral and singly ionized aluminium that can be used to improve the interpretation of abundances in stars. Paper II demonstrates a novel method, in which the atomic structure calculations of isotope shifts are combined with experimental data, for extracting nuclear properties other than the charge radii.
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| 8. |
- Papoulia, Asimina, et al.
(författare)
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Coulomb (Velocity) Gauge Recommended in Multiconfiguration Calculations of Transition Data Involving Rydberg Series
- 2019
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Ingår i: Atoms. - : MDPI. - 2218-2004. ; 7:4
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Tidskriftsartikel (refereegranskat)abstract
- Astronomical spectroscopy has recently expanded into the near-infrared (nIR) wavelength region, raising the demands on atomic transition data. The interpretation of the observed spectra largely relies on theoretical results, and progress towards the production of accurate theoretical data must continuously be made. Spectrum calculations that target multiple atomic states at the same time are by no means trivial. Further, numerous atomic systems involve Rydberg series, which are associated with additional difficulties. In this work, we demonstrate how the challenges in the computations of Rydberg series can be handled in large-scale multiconfiguration Dirac-Hartree-Fock (MCDHF) and relativistic configuration interaction (RCI) calculations. By paying special attention to the construction of the radial orbital basis that builds the atomic state functions, transition data that are weakly sensitive to the choice of gauge can be obtained. Additionally, we show that the Babushkin gauge should not always be considered as the preferred gauge, and that, in the computations of transition data involving Rydberg series, the Coulomb gauge could be more appropriate for the analysis of astrophysical spectra. To illustrate the above, results from computations of transitions involving Rydberg series in the astrophysically important C IV and C III ions are presented and analyzed.
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| 9. |
- Papoulia, Asimina, et al.
(författare)
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Effect of realistic nuclear charge distributions on isotope shifts and progress towards the extraction of higher-order nuclear radial moments
- 2016
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 94:4
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Tidskriftsartikel (refereegranskat)abstract
- Atomic spectral lines from different isotopes display a small shift in energy, commonly referred to as the line isotope shift. One of the components of the isotope shift is the field shift, which depends on the extent and the shape of the nuclear charge density distribution. The purpose of this work is to investigate how sensitive field shifts are with respect to variations in the nuclear size and shape and what information of nuclear charge distributions can be extracted frommeasurements.Nuclear properties are obtained from nuclear density functional theory calculations based on the Skyrme-Hartree-Fock-Bogoliubov approach. These results are combined with multiconfiguration Dirac-Hartree-Fock methods to obtain realistic field shifts and it is seen that phenomena such as nuclear deformation and variations in the diffuseness of nuclear charge distributions give measurable contributions to the isotope shifts.Using a different approach,we demonstrate the possibility to extract information concerning the nuclear charge densities from the observed field shifts. We deduce that combining methods used in atomic and nuclear structure theory gives an improved description of field shifts and that extracting additional nuclear information from measured isotope shifts is possible in the near future with improved experimental methods.
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| 10. |
- Papoulia, Asimina, et al.
(författare)
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Extended transition rates and lifetimes in Al I and Al II from systematic multiconfiguration calculations
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 621
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Tidskriftsartikel (refereegranskat)abstract
- MultiConfiguration Dirac-Hartree-Fock (MCDHF) and relativistic configuration interaction (RCI) calculations were performed for 28 and 78 states in neutral and singly ionized aluminium, respectively. In Al I, the configurations of interest are 3s(2)nl for n = 3, 4, 5 with l = 0 to 4, as well as 3s3p(2) and 3s(2)6l for l = 0, 1, 2. In Al II, in addition to the ground configuration 3s(2), the studied configurations are 3snl with n = 3 to 6 and l = 0 to 5, 3p(2), 3s7s, 3s7p, and 3p3d. Valence and core-valence electron correlation effects are systematically accounted for through large configuration state function (CSF) expansions. Calculated excitation energies are found to be in excellent agreement with experimental data from the National Institute of Standards and Technology (NIST) database. Lifetimes and transition data for radiative electric dipole (E1) transitions are given and compared with results from previous calculations and available measurements for both Al I and Al II. The computed lifetimes of Al I are in very good agreement with the measured lifetimes in high-precision laser spectroscopy experiments. The present calculations provide a substantial amount of updated atomic data, including transition data in the infrared region. This is particularly important since the new generation of telescopes are designed for this region. There is a significant improvement in accuracy, in particular for the more complex system of neutral Al I. The complete tables of transition data are available at the CDS.
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