Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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369 pages, 1459 KiB  
Article
GRASP Manual for Users
by Per Jönsson, Gediminas Gaigalas, Charlotte Froese Fischer, Jacek Bieroń, Ian P. Grant, Tomas Brage, Jörgen Ekman, Michel Godefroid, Jon Grumer, Jiguang Li and Wenxian Li
Atoms 2023, 11(4), 68; https://doi.org/10.3390/atoms11040068 - 05 Apr 2023
Cited by 14 | Viewed by 3135
Abstract
grasp is a software package in Fortran 95, adapted to run in parallel under MPI, for research in atomic physics. The basic premise is that, given a wave function, any observed atomic property can be computed. Thus, the first step is always to [...] Read more.
grasp is a software package in Fortran 95, adapted to run in parallel under MPI, for research in atomic physics. The basic premise is that, given a wave function, any observed atomic property can be computed. Thus, the first step is always to determine a wave function. Different properties challenge the accuracy of the wave function in different ways. This software is distributed under the MIT Licence. Full article
(This article belongs to the Special Issue The General Relativistic Atomic Structure Package—GRASP)
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34 pages, 864 KiB  
Article
Atomic Data Assessment with PyNeb: Radiative and Electron Impact Excitation Rates for [Fe ii] and [Fe iii]
by Claudio Mendoza, José E. Méndez-Delgado, Manuel Bautista, Jorge García-Rojas and Christophe Morisset
Atoms 2023, 11(4), 63; https://doi.org/10.3390/atoms11040063 - 01 Apr 2023
Cited by 3 | Viewed by 1640
Abstract
We use the PyNeb 1.1.16 Python package to evaluate the atomic datasets available for the spectral modeling of [Fe ii] and [Fe iii], which list level energies, A-values, and effective collision strengths. Most datasets are reconstructed from the sources, and [...] Read more.
We use the PyNeb 1.1.16 Python package to evaluate the atomic datasets available for the spectral modeling of [Fe ii] and [Fe iii], which list level energies, A-values, and effective collision strengths. Most datasets are reconstructed from the sources, and new ones are incorporated to be compared with observed and measured benchmarks. For [Fe iii], we arrive at conclusive results that allow us to select the default datasets, while for [Fe ii], the conspicuous temperature dependency on the collisional data becomes a deterrent. This dependency is mainly due to the singularly low critical density of the 3d7a4F9/2 metastable level that strongly depends on both the radiative and collisional data, although the level populating by fluorescence pumping from the stellar continuum cannot be ruled out. A new version of PyNeb (1.1.17) is released containing the evaluated datasets. Full article
(This article belongs to the Special Issue Development and Perspectives of Atomic and Molecular Databases)
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14 pages, 902 KiB  
Article
The Shapes of Stellar Spectra
by Carlos Allende Prieto
Atoms 2023, 11(3), 61; https://doi.org/10.3390/atoms11030061 - 20 Mar 2023
Cited by 3 | Viewed by 1289
Abstract
Stellar atmospheres separate the hot and dense stellar interiors from the emptiness of space. Radiation escapes from the outermost layers of a star, carrying direct physical information. Underneath the atmosphere, the very high opacity keeps radiation thermalized and resembling a black body with [...] Read more.
Stellar atmospheres separate the hot and dense stellar interiors from the emptiness of space. Radiation escapes from the outermost layers of a star, carrying direct physical information. Underneath the atmosphere, the very high opacity keeps radiation thermalized and resembling a black body with the local temperature. In the atmosphere the opacity drops, and radiative energy leaks out, which is redistributed in wavelength according to the physical processes by which matter and radiation interact, in particular photoionization. In this article, I will evaluate the role of photoionization in shaping the stellar energy distribution of stars. To that end, I employ simple, state-of-the-art plane-parallel model atmospheres and a spectral synthesis code, dissecting the effects of photoionization from different chemical elements and species, for stars of different masses in the range of 0.3 to 2 M. I examine and interpret the changes in the observed spectral energy distributions of the stars as a function of the atmospheric parameters. The photoionization of atomic hydrogen and H are the most relevant contributors to the continuum opacity in the optical and near-infrared regions, while heavier elements become important in the ultraviolet region. In the spectra of the coolest stars (spectral types M and later), the continuum shape from photoionization is no longer recognizable due to the accumulation of lines, mainly from molecules. These facts have been known for a long time, but the calculations presented provide an updated quantitative evaluation and insight into the role of photoionization on the structure of stellar atmospheres. Full article
(This article belongs to the Special Issue Photoionization of Atoms)
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27 pages, 3766 KiB  
Review
Photoionization and Electron–Ion Recombination in Astrophysical Plasmas
by D. John Hillier
Atoms 2023, 11(3), 54; https://doi.org/10.3390/atoms11030054 - 09 Mar 2023
Cited by 3 | Viewed by 1549
Abstract
Photoionization and its inverse, electron–ion recombination, are key processes that influence many astrophysical plasmas (and gasses), and the diagnostics that we use to analyze the plasmas. In this review we provide a brief overview of the importance of photoionization and recombination in astrophysics. [...] Read more.
Photoionization and its inverse, electron–ion recombination, are key processes that influence many astrophysical plasmas (and gasses), and the diagnostics that we use to analyze the plasmas. In this review we provide a brief overview of the importance of photoionization and recombination in astrophysics. We highlight how the data needed for spectral analyses, and the required accuracy, varies considerably in different astrophysical environments. We then discuss photoionization processes, highlighting resonances in their cross-sections. Next we discuss radiative recombination, and low and high temperature dielectronic recombination. The possible suppression of low temperature dielectronic recombination (LTDR) and high temperature dielectronic recombination (HTDR) due to the radiation field and high densities is discussed. Finally we discuss a few astrophysical examples to highlight photoionization and recombination processes. Full article
(This article belongs to the Special Issue Photoionization of Atoms)
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14 pages, 1363 KiB  
Article
Robust Optimized Pulse Schemes for Atomic Fountain Interferometry
by Michael H. Goerz, Mark A. Kasevich and Vladimir S. Malinovsky
Atoms 2023, 11(2), 36; https://doi.org/10.3390/atoms11020036 - 10 Feb 2023
Cited by 6 | Viewed by 1551
Abstract
The robustness of an atomic fountain interferometer with respect to variations in the initial velocity of the atoms and deviations from the optimal pulse amplitude is examined. We numerically simulate the dynamics of an interferometer in momentum space with a maximum separation of [...] Read more.
The robustness of an atomic fountain interferometer with respect to variations in the initial velocity of the atoms and deviations from the optimal pulse amplitude is examined. We numerically simulate the dynamics of an interferometer in momentum space with a maximum separation of 20k and map out the expected signal contrast depending on the variance of the initial velocity distribution and the value of the laser field amplitude. We show that an excitation scheme based on rapid adiabatic passage significantly enhances the expected signal contrast, compared to the commonly used scheme consisting of a series of π/2 and π pulses. We demonstrate further substantial increase of the robustness by using optimal control theory to identify splitting and swapping pulses that perform well on an ensemble average of pulse amplitudes and velocities. Our results demonstrate the ability of optimal control to significantly enhance future implementations of atomic fountain interferometry. Full article
(This article belongs to the Special Issue Advances in and Prospects for Matter Wave Interferometry)
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27 pages, 1305 KiB  
Article
Ideas and Tools for Error Detection in Opacity Databases
by Jean-Christophe Pain and Patricia Croset
Atoms 2023, 11(2), 27; https://doi.org/10.3390/atoms11020027 - 02 Feb 2023
Cited by 1 | Viewed by 1399
Abstract
In this article, we propose several ideas and tools in order to check the reliability of radiative opacity and atomic physics databases. We first emphasize that it can be useful to verify that mathematical inequalities, which impose lower and upper bounds on the [...] Read more.
In this article, we propose several ideas and tools in order to check the reliability of radiative opacity and atomic physics databases. We first emphasize that it can be useful to verify that mathematical inequalities, which impose lower and upper bounds on the Rosseland and/or Planck mean opacities, are satisfied, either for pure elements or mixtures. In the second part, we discuss the intriguing law of anomalous numbers, also named Benford’s law, which enables one to detect errors in line-strength collections, required in order to perform fine-structure calculations. Finally, we point out and illustrate the importance of quantifying the uncertainties due to interpolations in the density-temperature opacity (or more generally atomic-data) tables and performing convergence checks, which are crucial in the accuracy-completeness compromise inherent in opacity computations. Full article
(This article belongs to the Special Issue Development and Perspectives of Atomic and Molecular Databases)
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25 pages, 761 KiB  
Article
Performance Tests and Improvements on the rmcdhf and rci Programs of GRASP
by Yanting Li, Jinqing Li, Changxian Song, Chunyu Zhang, Ran Si, Kai Wang, Michel Godefroid, Gediminas Gaigalas, Per Jönsson and Chongyang Chen
Atoms 2023, 11(1), 12; https://doi.org/10.3390/atoms11010012 - 13 Jan 2023
Cited by 5 | Viewed by 1658
Abstract
The latest published version of GRASP (General-purpose Relativistic Atomic Structure Package), i.e., GRASP2018, retains a few suboptimal subroutines/algorithms, which reflect the limited memory and file storage of computers available in the 1980s. Here we show how the efficiency of the relativistic self-consistent-field (SCF) [...] Read more.
The latest published version of GRASP (General-purpose Relativistic Atomic Structure Package), i.e., GRASP2018, retains a few suboptimal subroutines/algorithms, which reflect the limited memory and file storage of computers available in the 1980s. Here we show how the efficiency of the relativistic self-consistent-field (SCF) procedure of the multiconfiguration-Dirac–Hartree–Fock (MCDHF) method and the relativistic configuration-interaction (RCI) calculations can be improved significantly. Compared with the original GRASP codes, the present modified version reduces the CPU times by factors of a few tens or more. The MPI performances for all the original and modified codes are carefully analyzed. Except for diagonalization, all computational processes show good MPI scaling. Full article
(This article belongs to the Special Issue The General Relativistic Atomic Structure Package—GRASP)
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17 pages, 433 KiB  
Article
Quantum Electrodynamics of Dicke States: Resonant One-Photon Exchange Energy and Entangled Decay Rate
by Ulrich D. Jentschura and Chandra M. Adhikari
Atoms 2023, 11(1), 10; https://doi.org/10.3390/atoms11010010 - 10 Jan 2023
Cited by 2 | Viewed by 1426
Abstract
We calculate the fully retarded one-photon exchange interaction potential between electrically neutral, identical atoms, one of which is assumed to be in an excited state, by matching the scattering matrix (S matrix) element with the effective Hamiltonian. Based on the Feynman prescription, [...] Read more.
We calculate the fully retarded one-photon exchange interaction potential between electrically neutral, identical atoms, one of which is assumed to be in an excited state, by matching the scattering matrix (S matrix) element with the effective Hamiltonian. Based on the Feynman prescription, we obtain the imaginary part of the interaction energy. Our results lead to precise formulas for the distance-dependent enhancement and suppression of the decay rates of entangled superradiant and subradiant Dicke states (Bell states), as a function of the interatomic distance. The formulas include a long-range tail due to entanglement. We apply the result to an example calculation involving two hydrogen atoms, one of which is in an excited P state. Full article
(This article belongs to the Section Atom Based Quantum Technology)
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44 pages, 978 KiB  
Article
An Introduction to Relativistic Theory as Implemented in GRASP
by Per Jönsson, Michel Godefroid, Gediminas Gaigalas, Jörgen Ekman, Jon Grumer, Wenxian Li, Jiguang Li , Tomas Brage, Ian P. Grant, Jacek Bieroń and Charlotte Froese Fischer
Atoms 2023, 11(1), 7; https://doi.org/10.3390/atoms11010007 - 31 Dec 2022
Cited by 19 | Viewed by 4059
Abstract
Computational atomic physics continues to play a crucial role in both increasing the understanding of fundamental physics (e.g., quantum electrodynamics and correlation) and producing atomic data for interpreting observations from large-scale research facilities ranging from fusion reactors to high-power laser systems, space-based telescopes [...] Read more.
Computational atomic physics continues to play a crucial role in both increasing the understanding of fundamental physics (e.g., quantum electrodynamics and correlation) and producing atomic data for interpreting observations from large-scale research facilities ranging from fusion reactors to high-power laser systems, space-based telescopes and isotope separators. A number of different computational methods, each with their own strengths and weaknesses, is available to meet these tasks. Here, we review the relativistic multiconfiguration method as it applies to the General Relativistic Atomic Structure Package [grasp2018, C. Froese Fischer, G. Gaigalas, P. Jönsson, J. Bieroń, Comput. Phys. Commun. (2018). DOI: 10.1016/j.cpc.2018.10.032]. To illustrate the capacity of the package, examples of calculations of relevance for nuclear physics and astrophysics are presented. Full article
(This article belongs to the Special Issue The General Relativistic Atomic Structure Package—GRASP)
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7 pages, 404 KiB  
Article
Laboratory Search for Fe IX Solar Diagnostic Lines Using an Electron Beam Ion Trap
by Elmar Träbert, Peter Beiersdorfer, Gregory V. Brown, Natalie Hell, Jaan K. Lepson, Alexander J. Fairchild, Michael Hahn and Daniel W. Savin
Atoms 2022, 10(4), 115; https://doi.org/10.3390/atoms10040115 - 16 Oct 2022
Cited by 5 | Viewed by 1248
Abstract
The Fe IX spectrum features two lines in the extreme ultraviolet whose ratio has been rated among the best density diagnostics in the solar spectrum. One line is an E1-allowed intercombination transition at 244.909 Å, the other an E1-forbidden [...] Read more.
The Fe IX spectrum features two lines in the extreme ultraviolet whose ratio has been rated among the best density diagnostics in the solar spectrum. One line is an E1-allowed intercombination transition at 244.909 Å, the other an E1-forbidden M2 transition at 241.739 Å. Employing a medium and a high resolution spectrometer at the Livermore EBIT-I electron beam ion trap, we have observed the line pair in the laboratory for the first time. Using a CHIANTI model computation, the observed line ratio yields a value of the electron density that is compatible with typical densities in our device. Full article
(This article belongs to the Special Issue 20th International Conference on the Physics of Highly Charged Ions)
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8 pages, 426 KiB  
Article
Shake-Off Process in Non-Sequential Single-Photon Double Ionization of Closed-Shell Atomic Targets
by Anatoli S. Kheifets
Atoms 2022, 10(3), 89; https://doi.org/10.3390/atoms10030089 - 07 Sep 2022
Cited by 7 | Viewed by 1596
Abstract
Amusia and Kheifets in 1984 introduced a Green’s function formalism to describe the effect of many-electron correlation on the ionization spectra of atoms. Here, we exploit this formalism to model the shake-off (SO) process, leading to the non-sequential single-photon two-electron ionization (double photoionization—DPI) [...] Read more.
Amusia and Kheifets in 1984 introduced a Green’s function formalism to describe the effect of many-electron correlation on the ionization spectra of atoms. Here, we exploit this formalism to model the shake-off (SO) process, leading to the non-sequential single-photon two-electron ionization (double photoionization—DPI) of closed-shell atomic targets. We separate the SO process from another knock-out (KO) mechanism of DPI and show the SO prevalence away from the DPI threshold. We use this kinematic regime to validate our model by making a comparison with more elaborate techniques, such as convergent and time-dependent close coupling. We also use our model to evaluate the attosecond time delay associated with the SO process. Typically, the SO is very fast, taking only a few attoseconds to complete. However, it can take much longer in the DPI of strongly correlated systems, such as the H ion as well as the subvalent shells of the Ar and Xe atoms and Cl ion. Full article
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21 pages, 2374 KiB  
Review
Recent Progress in Low-Energy Electron Elastic-Collisions with Multi-Electron Atoms and Fullerene Molecules
by Alfred Z. Msezane and Zineb Felfli
Atoms 2022, 10(3), 79; https://doi.org/10.3390/atoms10030079 - 29 Jul 2022
Cited by 3 | Viewed by 1758
Abstract
We briefly review recent applications of the Regge pole analysis to low-energy 0.0 ≤ E ≤ 10.0 eV electron elastic collisions with large multi-electron atoms and fullerene molecules. We then conclude with a demonstration of the sensitivity of the Regge pole-calculated Ramsauer–Townsend minima [...] Read more.
We briefly review recent applications of the Regge pole analysis to low-energy 0.0 ≤ E ≤ 10.0 eV electron elastic collisions with large multi-electron atoms and fullerene molecules. We then conclude with a demonstration of the sensitivity of the Regge pole-calculated Ramsauer–Townsend minima and shape resonances to the electronic structure and dynamics of the Bk and Cf actinide atoms, and their first time ever use as novel and rigorous validation of the recent experimental observation that identified Cf as a transitional element in the actinide series. Full article
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8 pages, 2046 KiB  
Article
The NEXT Project: Towards Production and Investigation of Neutron-Rich Heavy Nuclides
by Julia Even, Xiangcheng Chen, Arif Soylu, Paul Fischer, Alexander Karpov, Vyacheslav Saiko, Jan Saren, Moritz Schlaich, Thomas Schlathölter, Lutz Schweikhard, Juha Uusitalo and Frank Wienholtz
Atoms 2022, 10(2), 59; https://doi.org/10.3390/atoms10020059 - 01 Jun 2022
Cited by 4 | Viewed by 2480
Abstract
The heaviest actinide elements are only accessible in accelerator-based experiments on a one-atom-at-a-time level. Usually, fusion–evaporation reactions are applied to reach these elements. However, access to the neutron-rich isotopes is limited. An alternative reaction mechanism to fusion–evaporation is multinucleon transfer, which features higher [...] Read more.
The heaviest actinide elements are only accessible in accelerator-based experiments on a one-atom-at-a-time level. Usually, fusion–evaporation reactions are applied to reach these elements. However, access to the neutron-rich isotopes is limited. An alternative reaction mechanism to fusion–evaporation is multinucleon transfer, which features higher cross-sections. The main drawback of this technique is the wide angular distribution of the transfer products, which makes it challenging to catch and prepare them for precision measurements. To overcome this obstacle, we are building the NEXT experiment: a solenoid magnet is used to separate the different transfer products and to focus those of interest into a gas-catcher, where they are slowed down. From the gas-catcher, the ions are transferred and bunched by a stacked-ring ion guide into a multi-reflection time-of-flight mass spectrometer (MR-ToF MS). The MR-ToF MS provides isobaric separation and allows for precision mass measurements. In this article, we will give an overview of the NEXT experiment and its perspectives for future actinide research. Full article
(This article belongs to the Special Issue Atomic Structure of the Heaviest Elements)
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30 pages, 2572 KiB  
Review
Repulsive Fermi and Bose Polarons in Quantum Gases
by Francesco Scazza, Matteo Zaccanti, Pietro Massignan, Meera M. Parish and Jesper Levinsen
Atoms 2022, 10(2), 55; https://doi.org/10.3390/atoms10020055 - 27 May 2022
Cited by 28 | Viewed by 3740
Abstract
Polaron quasiparticles are formed when a mobile impurity is coupled to the elementary excitations of a many-particle background. In the field of ultracold atoms, the study of the associated impurity problem has attracted a growing interest over the last fifteen years. Polaron quasiparticle [...] Read more.
Polaron quasiparticles are formed when a mobile impurity is coupled to the elementary excitations of a many-particle background. In the field of ultracold atoms, the study of the associated impurity problem has attracted a growing interest over the last fifteen years. Polaron quasiparticle properties are essential to our understanding of a variety of paradigmatic quantum many-body systems realized in ultracold atomic gases and in the solid state, from imbalanced Bose–Fermi and Fermi–Fermi mixtures to fermionic Hubbard models. In this topical review, we focus on the so-called repulsive polaron branch, which emerges as an excited many-body state in systems with underlying attractive interactions such as ultracold atomic mixtures, and is characterized by an effective repulsion between the impurity and the surrounding medium. We give a brief account of the current theoretical and experimental understanding of repulsive polaron properties, for impurities embedded in both fermionic and bosonic media, and we highlight open issues deserving future investigations. Full article
(This article belongs to the Special Issue Physics of Impurities in Quantum Gases)
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9 pages, 294 KiB  
Article
Electronic Structure of Lr+ (Z = 103) from Ab Initio Calculations
by Harry Ramanantoanina, Anastasia Borschevsky, Michael Block and Mustapha Laatiaoui
Atoms 2022, 10(2), 48; https://doi.org/10.3390/atoms10020048 - 09 May 2022
Cited by 6 | Viewed by 1890
Abstract
The four-component relativistic Dirac–Coulomb Hamiltonian and the multireference configuration interaction (MRCI) model were used to provide the reliable energy levels and spectroscopic properties of the Lr+ ion and the Lu+ homolog. The energy spectrum of Lr+ is very similar to [...] Read more.
The four-component relativistic Dirac–Coulomb Hamiltonian and the multireference configuration interaction (MRCI) model were used to provide the reliable energy levels and spectroscopic properties of the Lr+ ion and the Lu+ homolog. The energy spectrum of Lr+ is very similar to that of the Lu+ homolog, with the multiplet manifold of the 7s2, 6d17s1 and 7s17p1 configurations as the ground and low-lying excited states. The results are discussed in light of earlier findings utilizing different theoretical models. Overall, the MRCI model can reliably predict the energy levels and properties and bring new insight into experiments with superheavy ions. Full article
(This article belongs to the Special Issue Atomic Structure of the Heaviest Elements)
8 pages, 21397 KiB  
Article
Demonstration of a Compact Magneto-Optical Trap on an Unstaffed Aerial Vehicle
by Luuk Earl, Jamie Vovrosh, Michael Wright, Daniel Roberts, Jonathan Winch, Marisa Perea-Ortiz, Andrew Lamb, Farzad Hayati, Paul Griffin, Nicole Metje, Kai Bongs and Michael Holynski
Atoms 2022, 10(1), 32; https://doi.org/10.3390/atoms10010032 - 17 Mar 2022
Cited by 6 | Viewed by 4349
Abstract
The extraordinary performance offered by cold atom-based clocks and sensors has the opportunity to profoundly affect a range of applications, for example in gravity surveys, enabling long term monitoring applications through low drift measurements. While ground-based devices are already starting to enter the [...] Read more.
The extraordinary performance offered by cold atom-based clocks and sensors has the opportunity to profoundly affect a range of applications, for example in gravity surveys, enabling long term monitoring applications through low drift measurements. While ground-based devices are already starting to enter the commercial market, significant improvements in robustness and reductions to size, weight, and power are required for such devices to be deployed by Unstaffed Aerial Vehicle systems (UAV). In this article, we realise the first step towards the deployment of cold atom based clocks and sensors on UAV’s by demonstrating an UAV portable magneto-optical trap system, the core package of cold atom based systems. This system is able to generate clouds of 2.1±0.2×107 atoms, in a package of 370 mm × 350 mm × 100 mm, weighing 6.56 kg, consuming 80 W of power. Full article
(This article belongs to the Special Issue Applications of Cold-Atom-Based Quantum Technology)
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10 pages, 1125 KiB  
Article
Ultra-Dilute Gas of Polarons in a Bose–Einstein Condensate
by Luis A. Peña Ardila
Atoms 2022, 10(1), 29; https://doi.org/10.3390/atoms10010029 - 02 Mar 2022
Cited by 5 | Viewed by 2999
Abstract
We investigate the properties of a dilute gas of impurities embedded in an ultracold gas of bosons that forms a Bose–Einstein condensate (BEC). This work focuses mainly on the equation of state (EoS) of the impurity gas at zero temperature and the induced [...] Read more.
We investigate the properties of a dilute gas of impurities embedded in an ultracold gas of bosons that forms a Bose–Einstein condensate (BEC). This work focuses mainly on the equation of state (EoS) of the impurity gas at zero temperature and the induced interaction between impurities mediated by the host bath. We use perturbative field-theory approaches, such as Hugenholtz–Pines formalism, in the weakly interacting regime. In turn, for strong interactions, we aim at non-perturbative techniques such as quantum–Monte Carlo (QMC) methods. Our findings agree with experimental observations for an ultra dilute gas of impurities, modeled in the framework of the single impurity problem; however, as the density of impurities increases, systematic deviations are displayed with respect to the one-body Bose polaron problem. Full article
(This article belongs to the Special Issue Physics of Impurities in Quantum Gases)
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12 pages, 3387 KiB  
Article
Persistent Planar Tetracoordinate Carbon in Global Minima Structures of Silicon-Carbon Clusters
by Luis Leyva-Parra, Diego Inostroza, Osvaldo Yañez, Julio César Cruz, Jorge Garza, Víctor García and William Tiznado
Atoms 2022, 10(1), 27; https://doi.org/10.3390/atoms10010027 - 28 Feb 2022
Cited by 11 | Viewed by 2936
Abstract
Recently, we reported a series of global minima whose structures consist of carbon rings decorated with heavier group 14 elements. Interestingly, these structures feature planar tetracoordinate carbons (ptCs) and result from the replacement of five or six protons (H+) from the [...] Read more.
Recently, we reported a series of global minima whose structures consist of carbon rings decorated with heavier group 14 elements. Interestingly, these structures feature planar tetracoordinate carbons (ptCs) and result from the replacement of five or six protons (H+) from the cyclopentadienyl anion (C5H5) or the pentalene dianion (C8H62−) by three or four E2+ dications (E = Si–Pb), respectively. The silicon derivatives of these series are the Si3C5 and Si4C8 clusters. Here we show that ptC persists in some clusters with an equivalent number of C and Si atoms, i.e., Si5C5, Si8C8, and Si9C9. In all these species, the ptC is embedded in a pentagonal C5 ring and participates in a three-center, two-electron (3c-2e) Si-ptC-Si σ-bond. Furthermore, these clusters are π-aromatic species according to chemical bonding analysis and magnetic criteria. Full article
(This article belongs to the Special Issue Planar Tetracoordinate Carbon—Fifty Years and Beyond)
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10 pages, 2285 KiB  
Article
Structure Calculations in Nd III and U III Relevant for Kilonovae Modelling
by Ricardo F. Silva, Jorge M. Sampaio, Pedro Amaro, Andreas Flörs, Gabriel Martínez-Pinedo and José P. Marques
Atoms 2022, 10(1), 18; https://doi.org/10.3390/atoms10010018 - 07 Feb 2022
Cited by 8 | Viewed by 2244
Abstract
The detection of gravitational waves and electromagnetic signals from the neutron star merger GW170817 has provided evidence that these astrophysical events are sites where the r-process nucleosynthesis operates. The electromagnetic signal, commonly known as kilonova, is powered by the radioactive decay of [...] Read more.
The detection of gravitational waves and electromagnetic signals from the neutron star merger GW170817 has provided evidence that these astrophysical events are sites where the r-process nucleosynthesis operates. The electromagnetic signal, commonly known as kilonova, is powered by the radioactive decay of freshly synthesized nuclei. However, its luminosity, colour and spectra depend on the atomic opacities of the produced elements. In particular, opacities of lanthanides and actinides elements, due to their large density of bound–bound transitions, are fundamental. The current work focuses on atomic structure calculations for lanthanide and actinide ions, which are important in kilonovae modelling of ejecta spectra. Calculations for Nd III and U III, two representative rare-earth ions, were achieved. Our aim is to provide valuable insights for future opacity calculations for all heavy elements. We noticed that the opacity of U III is about an order of magnitude greater than the opacity of Nd III due to a higher density of levels in the case of the actinide. Full article
(This article belongs to the Special Issue Atomic Structure of the Heaviest Elements)
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16 pages, 1005 KiB  
Article
Level Structure and Properties of Open f-Shell Elements
by Stephan Fritzsche
Atoms 2022, 10(1), 7; https://doi.org/10.3390/atoms10010007 - 12 Jan 2022
Cited by 10 | Viewed by 2842
Abstract
Open f-shell elements still constitute a great challenge for atomic theory owing to their (very) rich fine-structure and strong correlations among the valence-shell electrons. For these medium and heavy elements, many atomic properties are sensitive to the correlated motion of electrons and, [...] Read more.
Open f-shell elements still constitute a great challenge for atomic theory owing to their (very) rich fine-structure and strong correlations among the valence-shell electrons. For these medium and heavy elements, many atomic properties are sensitive to the correlated motion of electrons and, hence, require large-scale computations in order to deal consistently with all relativistic, correlation and rearrangement contributions to the electron density. Often, different concepts and notations need to be combined for just classifying the low-lying level structure of these elements. With Jac, the Jena Atomic Calculator, we here provide a toolbox that helps to explore and deal with such elements with open d- and f-shell structures. Based on Dirac’s equation, Jac is suitable for almost all atoms and ions across the periodic table. As an example, we demonstrate how reasonably accurate computations can be performed for the low-lying level structure, transition probabilities and lifetimes for Th2+ ions with a 5f6d ground configuration. Other, and more complex, shell structures are supported as well, though often for a trade-off between the size and accuracy of the computations. Owing to its simple use, however, Jac supports both quick estimates and detailed case studies on open d- or f-shell elements. Full article
(This article belongs to the Special Issue Atomic Structure of the Heaviest Elements)
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29 pages, 3571 KiB  
Article
Pattern Formation in One-Dimensional Polaron Systems and Temporal Orthogonality Catastrophe
by Georgios M. Koutentakis, Simeon I. Mistakidis and Peter Schmelcher
Atoms 2022, 10(1), 3; https://doi.org/10.3390/atoms10010003 - 28 Dec 2021
Cited by 10 | Viewed by 2250
Abstract
Recent studies have demonstrated that higher than two-body bath-impurity correlations are not important for quantitatively describing the ground state of the Bose polaron. Motivated by the above, we employ the so-called Gross Ansatz (GA) approach to unravel the stationary and dynamical properties of [...] Read more.
Recent studies have demonstrated that higher than two-body bath-impurity correlations are not important for quantitatively describing the ground state of the Bose polaron. Motivated by the above, we employ the so-called Gross Ansatz (GA) approach to unravel the stationary and dynamical properties of the homogeneous one-dimensional Bose-polaron for different impurity momenta and bath-impurity couplings. We explicate that the character of the equilibrium state crossovers from the quasi-particle Bose polaron regime to the collective-excitation stationary dark-bright soliton for varying impurity momentum and interactions. Following an interspecies interaction quench the temporal orthogonality catastrophe is identified, provided that bath-impurity interactions are sufficiently stronger than the intraspecies bath ones, thus generalizing the results of the confined case. This catastrophe originates from the formation of dispersive shock wave structures associated with the zero-range character of the bath-impurity potential. For initially moving impurities, a momentum transfer process from the impurity to the dispersive shock waves via the exerted drag force is demonstrated, resulting in a final polaronic state with reduced velocity. Our results clearly demonstrate the crucial role of non-linear excitations for determining the behavior of the one-dimensional Bose polaron. Full article
(This article belongs to the Special Issue Physics of Impurities in Quantum Gases)
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13 pages, 500 KiB  
Article
Electron Scattering Cross-Section Calculations for Atomic and Molecular Iodine
by Harindranath B. Ambalampitiya, Kathryn R. Hamilton, Oleg Zatsarinny, Klaus Bartschat, Matt A. P. Turner, Anna Dzarasova and Jonathan Tennyson
Atoms 2021, 9(4), 103; https://doi.org/10.3390/atoms9040103 - 30 Nov 2021
Cited by 10 | Viewed by 3538
Abstract
Cross sections for electron scattering from atomic and molecular iodine are calculated based on the R-matrix (close-coupling) method. Elastic and electronic excitation cross sections are presented for both I and I2. The dissociative electron attachment and vibrational excitation cross sections [...] Read more.
Cross sections for electron scattering from atomic and molecular iodine are calculated based on the R-matrix (close-coupling) method. Elastic and electronic excitation cross sections are presented for both I and I2. The dissociative electron attachment and vibrational excitation cross sections of the iodine molecule are obtained using the local complex potential approximation. Ionization cross sections are also computed for I2 using the BEB model. Full article
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14 pages, 3598 KiB  
Article
Evaluation of Recommended Cross Sections for the Simulation of Electron Tracks in Water
by Adrián García-Abenza, Ana I. Lozano, Juan C. Oller, Francisco Blanco, Jimena D. Gorfinkiel, Paulo Limão-Vieira and Gustavo García
Atoms 2021, 9(4), 98; https://doi.org/10.3390/atoms9040098 - 22 Nov 2021
Cited by 9 | Viewed by 2257
Abstract
The accuracy of the most recent recommended cross sections dataset for electron scattering from gaseous H2O (J. Phys. Chem. Ref. Data 2021, 50, 023103) is probed in a joint experimental and computational study. Simulations of the magnetically [...] Read more.
The accuracy of the most recent recommended cross sections dataset for electron scattering from gaseous H2O (J. Phys. Chem. Ref. Data 2021, 50, 023103) is probed in a joint experimental and computational study. Simulations of the magnetically confined electron transport through a gas cell containing H2O for different beam energies (3, 10 and 70 eV) and pressures (2.5 to 20.0 mTorr) have been performed by using a specifically designed Monte Carlo code. The simulated results have been compared with the corresponding experimental data as well as with simulations performed with Geant4DNA. The comparison made between the experiment and simulation provides insight into possible improvement of the recommended dataset. Full article
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10 pages, 471 KiB  
Article
Targeted Cross-Section Calculations for Plasma Simulations
by Sebastian Mohr, Maria Tudorovskaya, Martin Hanicinec and Jonathan Tennyson
Atoms 2021, 9(4), 85; https://doi.org/10.3390/atoms9040085 - 21 Oct 2021
Cited by 6 | Viewed by 1921
Abstract
Gathering data on electron collisions in plasmas is a vital part of conducting plasma simulations. However, data on neutral radicals and neutrals formed in the plasma by reactions between different radicals are usually not readily available. While these cross-sections can be calculated numerically, [...] Read more.
Gathering data on electron collisions in plasmas is a vital part of conducting plasma simulations. However, data on neutral radicals and neutrals formed in the plasma by reactions between different radicals are usually not readily available. While these cross-sections can be calculated numerically, this is a time-consuming process and it is not clear from the outset which additional cross-sections are needed for a given plasma process. Hence, identifying species for which additional cross-sections are needed in advance is highly advantageous. Here, we present a structured approach to do this. In this, a chemistry set using estimated data for unknown electron collisions is run in a global plasma model. The results are used to rank the species with regard to their influence on densities of important species such as electrons or neutrals inducing desired surface processes. For this, an algorithm based on graph theory is used. The species ranking helps to make an informed decision on which cross-sections need to be calculated to improve the chemistry set and which can be neglected to save time. The validity of this approach is demonstrated through an example in an SF6/O2 plasma. Full article
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12 pages, 1593 KiB  
Review
A Missing Puzzle in Dissociative Electron Attachment to Biomolecules: The Detection of Radicals
by Sylwia Ptasinska
Atoms 2021, 9(4), 77; https://doi.org/10.3390/atoms9040077 - 07 Oct 2021
Cited by 10 | Viewed by 2537
Abstract
Ionizing radiation releases a flood of low-energy electrons that often causes the fragmentation of the molecular species it encounters. Special attention has been paid to the electrons’ contribution to DNA damage via the dissociative electron attachment (DEA) process. Although numerous research groups worldwide [...] Read more.
Ionizing radiation releases a flood of low-energy electrons that often causes the fragmentation of the molecular species it encounters. Special attention has been paid to the electrons’ contribution to DNA damage via the dissociative electron attachment (DEA) process. Although numerous research groups worldwide have probed these processes in the past, and many significant achievements have been made, some technical challenges have hindered researchers from obtaining a complete picture of DEA. Therefore, this research perspective calls urgently for the implementation of advanced techniques to identify non-charged radicals that form from such a decomposition of gas-phase molecules. Having well-described DEA products offers a promise to benefit society by straddling the boundary between physics, chemistry, and biology, and it brings the tools of atomic and molecular physics to bear on relevant issues of radiation research and medicine. Full article
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8 pages, 1738 KiB  
Article
Revealing the Target Electronic Structure with Under-Threshold RABBITT
by Anatoli Kheifets
Atoms 2021, 9(3), 66; https://doi.org/10.3390/atoms9030066 - 13 Sep 2021
Cited by 12 | Viewed by 1954
Abstract
The process of reconstruction of attosecond beating by interference of two-photon transitions (RABBITT) reveals the target atom electronic structure when one of the transitions proceeds from below the ionization threshold. Such an under-threshold RABBITT resonates with the target bound states and thus maps [...] Read more.
The process of reconstruction of attosecond beating by interference of two-photon transitions (RABBITT) reveals the target atom electronic structure when one of the transitions proceeds from below the ionization threshold. Such an under-threshold RABBITT resonates with the target bound states and thus maps faithfully the discrete energy levels and the corresponding oscillator strengths. We demonstrate this sensitivity by considering the Ne atom driven by the combination of the XUV and IR pulses at the fundamental laser frequency in the 800 and 1000 nm ranges. Full article
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11 pages, 2406 KiB  
Article
Cross Sections and Rate Coefficients for Vibrational Excitation of H2O by Electron Impact
by Mehdi Ayouz, Alexandre Faure, Jonathan Tennyson, Maria Tudorovskaya and Viatcheslav Kokoouline
Atoms 2021, 9(3), 62; https://doi.org/10.3390/atoms9030062 - 06 Sep 2021
Cited by 7 | Viewed by 2130
Abstract
Cross-sections and thermally averaged rate coefficients for vibration (de-)excitation of a water molecule by electron impact are computed; one and two quanta excitations are considered for all three normal modes. The calculations use a theoretical approach that combines the normal mode approximation for [...] Read more.
Cross-sections and thermally averaged rate coefficients for vibration (de-)excitation of a water molecule by electron impact are computed; one and two quanta excitations are considered for all three normal modes. The calculations use a theoretical approach that combines the normal mode approximation for vibrational states of water, a vibrational frame transformation employed to evaluate the scattering matrix for vibrational transitions and the UK molecular R-matrix code. The interval of applicability of the rate coefficients is from 10 to 10,000 K. A comprehensive set of calculations is performed to assess uncertainty of the obtained data. The results should help in modelling non-LTE spectra of water in various astrophysical environments. Full article
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19 pages, 3238 KiB  
Article
Accurate Electron Drift Mobility Measurements in Moderately Dense Helium Gas at Several Temperatures
by Armando Francesco Borghesani
Atoms 2021, 9(3), 52; https://doi.org/10.3390/atoms9030052 - 04 Aug 2021
Cited by 8 | Viewed by 1997
Abstract
We report new accurate measurements of the drift mobility μ of quasifree electrons in moderately dense helium gas in the temperature range 26KT300K for densities lower than those at which states of electrons localized in bubbles appear. [...] Read more.
We report new accurate measurements of the drift mobility μ of quasifree electrons in moderately dense helium gas in the temperature range 26KT300K for densities lower than those at which states of electrons localized in bubbles appear. By heuristically including multiple-scattering effects into classical kinetic formulas, as previously done for neon and argon, an excellent description of the field E, density N, and temperature T dependence of μ is obtained. Moreover, the experimental evidence suggests that the strong decrease of the zero-field density-normalized mobility μ0N with increasing N from the low up to intermediate density regime is mainly due to weak localization of electrons caused by the intrinsic disorder of the system, whereas the further decrease of μ0N for even larger N is due to electron self-trapping in cavities. We suggest that a distinction between weakly localized and electron bubble states can be done by inspecting the behavior of μ0N as a function of N at intermediate densities. Full article
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14 pages, 763 KiB  
Article
Towards B-Spline Atomic Structure Calculations
by Charlotte Froese Fischer
Atoms 2021, 9(3), 50; https://doi.org/10.3390/atoms9030050 - 31 Jul 2021
Cited by 5 | Viewed by 2006
Abstract
The paper reviews the history of B-spline methods for atomic structure calculations for bound states. It highlights various aspects of the variational method, particularly with regard to the orthogonality requirements, the iterative self-consistent method, the eigenvalue problem, and the related sphf, dbsr-hf, [...] Read more.
The paper reviews the history of B-spline methods for atomic structure calculations for bound states. It highlights various aspects of the variational method, particularly with regard to the orthogonality requirements, the iterative self-consistent method, the eigenvalue problem, and the related sphf, dbsr-hf, and spmchf programs. B-splines facilitate the mapping of solutions from one grid to another. The following paper describes a two-stage approach where the goal of the first stage is to determine parameters of the problem, such as the range and approximate values of the orbitals, after which the level of accuracy is raised. Once convergence has been achieved the Virial Theorem, which is evaluated as a check for accuracy. For exact solutions, the V/T ratio for a non-relativistic calculation is −2. Full article
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37 pages, 4365 KiB  
Article
Self-Organization in Cold Atoms Mediated by Diffractive Coupling
by Thorsten Ackemann, Guillaume Labeyrie, Giuseppe Baio, Ivor Krešić, Josh G. M. Walker, Adrian Costa Boquete, Paul Griffin, William J. Firth, Robin Kaiser, Gian-Luca Oppo and Gordon R. M. Robb
Atoms 2021, 9(3), 35; https://doi.org/10.3390/atoms9030035 - 23 Jun 2021
Cited by 10 | Viewed by 3262
Abstract
This article discusses self-organization in cold atoms via light-mediated interactions induced by feedback from a single retro-reflecting mirror. Diffractive dephasing between the pump beam and the spontaneous sidebands selects the lattice period. Spontaneous breaking of the rotational and translational symmetry occur in the [...] Read more.
This article discusses self-organization in cold atoms via light-mediated interactions induced by feedback from a single retro-reflecting mirror. Diffractive dephasing between the pump beam and the spontaneous sidebands selects the lattice period. Spontaneous breaking of the rotational and translational symmetry occur in the 2D plane transverse to the pump. We elucidate how diffractive ripples couple sites on the self-induced atomic lattice. The nonlinear phase shift of the atomic cloud imprinted onto the optical beam is the parameter determining coupling strength. The interaction can be tailored to operate either on external degrees of freedom leading to atomic crystallization for thermal atoms and supersolids for a quantum degenerate gas, or on internal degrees of freedom like populations of the excited state or Zeeman sublevels. Using the light polarization degrees of freedom on the Poincaré sphere (helicity and polarization direction), specific irreducible tensor components of the atomic Zeeman states can be coupled leading to spontaneous magnetic ordering of states of dipolar and quadrupolar nature. The requirements for critical interaction strength are compared for the different situations. Connections and extensions to longitudinally pumped cavities, counterpropagating beam schemes and the CARL instability are discussed. Full article
(This article belongs to the Special Issue Collective Atomic and Free-Electron Lasing)
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15 pages, 2130 KiB  
Article
Long-Range Atom–Ion Rydberg Molecule: A Novel Molecular Binding Mechanism
by Markus Deiß, Shinsuke Haze and Johannes Hecker Denschlag
Atoms 2021, 9(2), 34; https://doi.org/10.3390/atoms9020034 - 21 Jun 2021
Cited by 21 | Viewed by 3141
Abstract
We present a novel binding mechanism where a neutral Rydberg atom and an atomic ion form a molecular bound state at a large internuclear distance. The binding mechanism is based on Stark shifts and level crossings that are induced in the Rydberg atom [...] Read more.
We present a novel binding mechanism where a neutral Rydberg atom and an atomic ion form a molecular bound state at a large internuclear distance. The binding mechanism is based on Stark shifts and level crossings that are induced in the Rydberg atom due to the electric field of the ion. At particular internuclear distances between the Rydberg atom and the ion, potential wells occur that can hold atom–ion molecular bound states. Apart from the binding mechanism, we describe important properties of the long-range atom–ion Rydberg molecule, such as its lifetime and decay paths, its vibrational and rotational structure, and its large dipole moment. Furthermore, we discuss methods of how to produce and detect it. The unusual properties of the long-range atom–ion Rydberg molecule give rise to interesting prospects for studies of wave packet dynamics in engineered potential energy landscapes. Full article
(This article belongs to the Special Issue Low Energy Interactions between Ions and Ultracold Alkali Atoms)
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13 pages, 2159 KiB  
Article
Few Body Effects in the Electron and Positron Impact Ionization of Atoms
by R.I. Campeanu and Colm T. Whelan
Atoms 2021, 9(2), 33; https://doi.org/10.3390/atoms9020033 - 09 Jun 2021
Cited by 5 | Viewed by 2239
Abstract
Triple differential cross sections (TDCS) are presented for the electron and positron impact ionization of inert gas atoms in a range of energy sharing geometries where a number of significant few body effects compete to define the shape of the TDCS. Using both [...] Read more.
Triple differential cross sections (TDCS) are presented for the electron and positron impact ionization of inert gas atoms in a range of energy sharing geometries where a number of significant few body effects compete to define the shape of the TDCS. Using both positrons and electrons as projectiles has opened up the possibility of performing complementary studies which could effectively isolate competing interactions that cannot be separately detected in an experiment with a single projectile. Results will be presented in kinematics where the electron impact ionization appears to be well understood and using the same kinematics positron cross sections will be presented. The kinematics are then varied in order to focus on the role of distortion, post collision interaction (pci), and interference effects. Full article
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32 pages, 903 KiB  
Review
A Review of High-Gain Free-Electron Laser Theory
by Nicola Piovella and Luca Volpe
Atoms 2021, 9(2), 28; https://doi.org/10.3390/atoms9020028 - 12 May 2021
Cited by 7 | Viewed by 2785
Abstract
High-gain free-electron lasers, conceived in the 1980s, are nowadays the only bright sources of coherent X-ray radiation available. In this article, we review the theory developed by R. Bonifacio and coworkers, who have been some of the first scientists envisaging its operation as [...] Read more.
High-gain free-electron lasers, conceived in the 1980s, are nowadays the only bright sources of coherent X-ray radiation available. In this article, we review the theory developed by R. Bonifacio and coworkers, who have been some of the first scientists envisaging its operation as a single-pass amplifier starting from incoherent undulator radiation, in the so called self-amplified spontaneous emission (SASE) regime. We review the FEL theory, discussing how the FEL parameters emerge from it, which are fundamental for describing, designing and understanding all FEL experiments in the high-gain, single-pass operation. Full article
(This article belongs to the Special Issue Collective Atomic and Free-Electron Lasing)
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12 pages, 4200 KiB  
Article
Route to Extend the Lifetime of a Discrete Time Crystal in a Finite Spin Chain without Disorder
by Sayan Choudhury
Atoms 2021, 9(2), 25; https://doi.org/10.3390/atoms9020025 - 12 Apr 2021
Cited by 4 | Viewed by 2902
Abstract
Periodically driven (Floquet) systems are described by time-dependent Hamiltonians that possess discrete time translation symmetry. The spontaneous breaking of this symmetry leads to the emergence of a novel non-equilibrium phase of matter—the Discrete Time Crystal (DTC). In this paper, we propose a scheme [...] Read more.
Periodically driven (Floquet) systems are described by time-dependent Hamiltonians that possess discrete time translation symmetry. The spontaneous breaking of this symmetry leads to the emergence of a novel non-equilibrium phase of matter—the Discrete Time Crystal (DTC). In this paper, we propose a scheme to extend the lifetime of a DTC in a paradigmatic model—a translation-invariant Ising spin chain with nearest-neighbor interaction J, subjected to a periodic kick by a transverse magnetic field with frequency 2πT. This system exhibits the hallmark signature of a DTC—persistent sub-harmonic oscillations with frequency πT—for a wide parameter regime. Employing both analytical arguments as well as exact diagonalization calculations, we demonstrate that the lifetime of the DTC is maximized, when the interaction strength is tuned to an optimal value, JT=π. Our proposal essentially relies on an interaction-induced quantum interference mechanism that suppresses the creation of excitations, and thereby enhances the DTC lifetime. Intriguingly, we find that the period doubling oscillations can last eternally in even size systems. This anomalously long lifetime can be attributed to a time reflection symmetry that emerges at JT=π. Our work provides a promising avenue for realizing a robust DTC in various quantum emulator platforms. Full article
(This article belongs to the Section Cold Atoms, Quantum Gases and Bose-Einstein Condensation)
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14 pages, 8961 KiB  
Article
CAl4Mg0/−: Global Minima with a Planar Tetracoordinate Carbon Atom
by Nisha Job, Maya Khatun, Krishnan Thirumoorthy, Sasanka Sankhar Reddy CH, Vijayanand Chandrasekaran, Anakuthil Anoop and Venkatesan S. Thimmakondu
Atoms 2021, 9(2), 24; https://doi.org/10.3390/atoms9020024 - 09 Apr 2021
Cited by 18 | Viewed by 4805
Abstract
Isomers of CAl4Mg and CAl4Mg have been theoretically characterized for the first time. The most stable isomer for both the neutral and anion contain a planar tetracoordinate carbon (ptC) atom. Unlike the isovalent CAl4Be case, which [...] Read more.
Isomers of CAl4Mg and CAl4Mg have been theoretically characterized for the first time. The most stable isomer for both the neutral and anion contain a planar tetracoordinate carbon (ptC) atom. Unlike the isovalent CAl4Be case, which contains a planar pentacoordinate carbon atom as the global minimum geometry, replacing beryllium with magnesium makes the ptC isomer the global minimum due to increased ionic radii of magnesium. However, it is relatively easier to conduct experimental studies for CAl4Mg0/− as beryllium is toxic. While the neutral molecule containing the ptC atom follows the 18 valence electron rule, the anion breaks the rule with 19 valence electrons. The electron affinity of CAl4Mg is in the range of 1.96–2.05 eV. Both the global minima exhibit π/σ double aromaticity. Ab initio molecular dynamics simulations were carried out for both the global minima at 298 K for 10 ps to confirm their kinetic stability. Full article
(This article belongs to the Special Issue Planar Tetracoordinate Carbon—Fifty Years and Beyond)
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25 pages, 1407 KiB  
Article
Polaron Problems in Ultracold Atoms: Role of a Fermi Sea across Different Spatial Dimensions and Quantum Fluctuations of a Bose Medium
by Hiroyuki Tajima, Junichi Takahashi, Simeon I. Mistakidis, Eiji Nakano and Kei Iida
Atoms 2021, 9(1), 18; https://doi.org/10.3390/atoms9010018 - 09 Mar 2021
Cited by 21 | Viewed by 3957
Abstract
The notion of a polaron, originally introduced in the context of electrons in ionic lattices, helps us to understand how a quantum impurity behaves when being immersed in and interacting with a many-body background. We discuss the impact of the impurities on the [...] Read more.
The notion of a polaron, originally introduced in the context of electrons in ionic lattices, helps us to understand how a quantum impurity behaves when being immersed in and interacting with a many-body background. We discuss the impact of the impurities on the medium particles by considering feedback effects from polarons that can be realized in ultracold quantum gas experiments. In particular, we exemplify the modifications of the medium in the presence of either Fermi or Bose polarons. Regarding Fermi polarons we present a corresponding many-body diagrammatic approach operating at finite temperatures and discuss how mediated two- and three-body interactions are implemented within this framework. Utilizing this approach, we analyze the behavior of the spectral function of Fermi polarons at finite temperature by varying impurity-medium interactions as well as spatial dimensions from three to one. Interestingly, we reveal that the spectral function of the medium atoms could be a useful quantity for analyzing the transition/crossover from attractive polarons to molecules in three-dimensions. As for the Bose polaron, we showcase the depletion of the background Bose-Einstein condensate in the vicinity of the impurity atom. Such spatial modulations would be important for future investigations regarding the quantification of interpolaron correlations in Bose polaron problems. Full article
(This article belongs to the Special Issue Physics of Impurities in Quantum Gases)
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