Atoms

28 pages, 8131 KB

Open AccessEditor’s ChoiceArticle

Effects of Spiralling Trajectories on White Dwarf Spectra: High Rydberg States

by Spiros Alexiou

Atoms 2023, 11(11), 141; https://doi.org/10.3390/atoms11110141 - 1 Nov 2023

Cited by 5 | Viewed by 1719

It has been recently suggested that white dwarf diagnostics could be in error and should be revised because of the effect of the magnetic field on spiralling trajectories of the plasma particles (mainly electrons), predicting a dramatic width increase for high densities of [...] Read more.

It has been recently suggested that white dwarf diagnostics could be in error and should be revised because of the effect of the magnetic field on spiralling trajectories of the plasma particles (mainly electrons), predicting a dramatic width increase for high densities of Balmer-

β

and especially for the

δ

and

ϵ

lines. These suggestions overlook important physics and are shown here to be incorrect. Specifically, exact calculations are carried out that can assess the importance of various physical effects neglected in the erroneous analysis mentioned. The net result of accounting for spiralling electron trajectories is typically a small to modest reduction in the line widths, at least for the parameters considered. Full article

(This article belongs to the Special Issue Rydberg Atomic Physics)

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13 pages, 981 KB

Open AccessEditor’s ChoiceArticle

Multi-Reflection Time-of-Flight Mass Spectroscopy for Superheavy Nuclides

by Peter Schury, Yuta Ito, Toshitaka Niwase and Michiharu Wada

Atoms 2023, 11(10), 134; https://doi.org/10.3390/atoms11100134 - 17 Oct 2023

Cited by 1 | Viewed by 2214

Abstract

The atomic masses of isotopes of elements beyond fermium, which can presently only be produced online via fusion-evaporation reactions, have until recently been determined only from

α

decay chains reaching nuclides with known atomic masses. Especially in the case of lower-yield nuclides, for [...] Read more.

The atomic masses of isotopes of elements beyond fermium, which can presently only be produced online via fusion-evaporation reactions, have until recently been determined only from

α

decay chains reaching nuclides with known atomic masses. Especially in the case of lower-yield nuclides, for which the sufficiently detailed nuclear spectroscopy required to fully determine the nuclear structure is not possible, such indirect mass determinations may suffer systematic errors. For many superheavy nuclides, their decay chains end in spontaneous fission or in

β

-decay prior to reaching nuclides of known mass. To address this dearth of accurate atomic masses, we have developed a multi-reflection time-of-flight mass spectrograph that can make use of decay-correlations to accurately and precisely determine atomic masses for the very low-yield superheavy nuclides. Full article

(This article belongs to the Special Issue Advances in Ion Trapping of Radioactive Ions)

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11 pages, 603 KB

Open AccessEditor’s ChoiceArticle

The St. Benedict Facility: Probing Fundamental Symmetries through Mixed Mirror β-Decays

by William S. Porter, Daniel W. Bardayan, Maxime Brodeur, Daniel P. Burdette, Jason A. Clark, Aaron T. Gallant, Alicen M. Houff, James J. Kolata, Biying Liu, Patrick D. O’Malley, Caleb Quick, Fabio Rivero, Guy Savard, Adrian A. Valverde and Regan Zite

Atoms 2023, 11(10), 129; https://doi.org/10.3390/atoms11100129 - 11 Oct 2023

Cited by 2 | Viewed by 1992

Abstract

Precise measurements of nuclear beta decays provide a unique insight into the Standard Model due to their connection to the electroweak interaction. These decays help constrain the unitarity or non-unitarity of the Cabibbo–Kobayashi–Maskawa (CKM) quark mixing matrix, and can uniquely probe the existence [...] Read more.

Precise measurements of nuclear beta decays provide a unique insight into the Standard Model due to their connection to the electroweak interaction. These decays help constrain the unitarity or non-unitarity of the Cabibbo–Kobayashi–Maskawa (CKM) quark mixing matrix, and can uniquely probe the existence of exotic scalar or tensor currents. Of these decays, superallowed mixed mirror transitions have been the least well-studied, in part due to the absence of data on their Fermi to Gamow-Teller mixing ratios (

ρ

). At the Nuclear Science Laboratory (NSL) at the University of Notre Dame, the Superallowed Transition Beta-Neutrino Decay Ion Coincidence Trap (St. Benedict) is being constructed to determine the

ρ

for various mirror decays via a measurement of the beta–neutrino angular correlation parameter (

a_{β ν}

) to a relative precision of 0.5%. In this work, we present an overview of the St. Benedict facility and the impact it will have on various Beyond the Standard Model studies, including an expanded sensitivity study of

ρ

for various mirror nuclei accessible to the facility. A feasibility evaluation is also presented that indicates the measurement goals for many mirror nuclei, which are currently attainable in a week of radioactive beam delivery at the NSL. Full article

(This article belongs to the Special Issue Advances in Ion Trapping of Radioactive Ions)

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16 pages, 6966 KB

Open AccessEditor’s ChoiceArticle

Status of CHIP-TRAP: The Central Michigan University High-Precision Penning Trap

by Matthew Redshaw, Ramesh Bhandari, Nadeesha Gamage, Mehedi Hasan, Madhawa Horana Gamage, Dakota K. Keblbeck, Savannah Limarenko and Dilanka Perera

Atoms 2023, 11(10), 127; https://doi.org/10.3390/atoms11100127 - 7 Oct 2023

Cited by 1 | Viewed by 2405

Abstract

Precise and accurate atomic mass data provide crucial information for applications in a wide range of fields in physics and beyond, including astrophysics, nuclear structure, particle and neutrino physics, fundamental symmetries, chemistry, and metrology. The most precise atomic mass measurements are performed on [...] Read more.

Precise and accurate atomic mass data provide crucial information for applications in a wide range of fields in physics and beyond, including astrophysics, nuclear structure, particle and neutrino physics, fundamental symmetries, chemistry, and metrology. The most precise atomic mass measurements are performed on charged particles confined in a Penning trap. Here, we describe the development, status, and outlook of CHIP-TRAP: the Central Michigan University high-precision Penning trap. CHIP-TRAP aims to perform ultra-high precision (∼1 part in 10

^{11}

fractional precision) mass measurements on stable and long-lived isotopes produced with external ion sources and transported to the Penning traps. Along the way, ions of a particular

m / q

are selected with a multi-reflection time-of-flight mass separator (MR-TOF-MS), with further filtering performed in a cylindrical capture trap before the ions are transported to a pair of hyperbolic measurement traps. In this paper, we report on the design and status of CHIP-TRAP and present results from the commissioning of the ion sources, MR-TOF-MS, and capture trap. We also provide an outlook on the continued development and commissioning of CHIP-TRAP. Full article

(This article belongs to the Special Issue Advances in Ion Trapping of Radioactive Ions)

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13 pages, 3652 KB

Open AccessEditor’s ChoiceArticle

Extreme Ultraviolet Radiation Sources from Dense Plasmas

by Klaus Bergmann

Atoms 2023, 11(9), 118; https://doi.org/10.3390/atoms11090118 - 31 Aug 2023

Cited by 4 | Viewed by 2371

Abstract

The concept of dense and hot plasmas can be used to build up powerful and brilliant radiation sources in the soft X-ray and extreme ultraviolet spectral range. Such sources are used for nanoscale imaging and structuring applications, such as EUV lithography in the [...] Read more.

The concept of dense and hot plasmas can be used to build up powerful and brilliant radiation sources in the soft X-ray and extreme ultraviolet spectral range. Such sources are used for nanoscale imaging and structuring applications, such as EUV lithography in the semiconductor industry. An understanding of light-generating atomic processes and radiation transport within the plasma is mandatory for optimization. The basic principles and technical concepts using either a pulsed laser or a gas discharge for plasma generation are presented, and critical aspects in the ionization dynamics are outlined within the framework of a simplified atomic physics model. Full article

(This article belongs to the Special Issue Atomic Physics in Dense Plasmas)

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93 pages, 4232 KB

Open AccessEditor’s ChoiceReview

Shape Coexistence in Even–Even Nuclei: A Theoretical Overview

by Dennis Bonatsos, Andriana Martinou, Spyridon K. Peroulis, Theodoros J. Mertzimekis and Nikolay Minkov

Atoms 2023, 11(9), 117; https://doi.org/10.3390/atoms11090117 - 30 Aug 2023

Cited by 21 | Viewed by 5532

Abstract

The last decade has seen a rapid growth in our understanding of the microscopic origins of shape coexistence, assisted by the new data provided by the modern radioactive ion beam facilities built worldwide. Islands of the nuclear chart in which shape coexistence can [...] Read more.

The last decade has seen a rapid growth in our understanding of the microscopic origins of shape coexistence, assisted by the new data provided by the modern radioactive ion beam facilities built worldwide. Islands of the nuclear chart in which shape coexistence can occur have been identified, and the different microscopic particle–hole excitation mechanisms leading to neutron-induced or proton-induced shape coexistence have been clarified. The relation of shape coexistence to the islands of inversion, appearing in light nuclei, to the new spin-aligned phase appearing in

N = Z

nuclei, as well as to shape/phase transitions occurring in medium mass and heavy nuclei, has been understood. In the present review, these developments are considered within the shell-model and mean-field approaches, as well as by symmetry methods. In addition, based on systematics of data, as well as on symmetry considerations, quantitative rules are developed, predicting regions in which shape coexistence can appear, as a possible guide for further experimental efforts that can help in improving our understanding of the details of the nucleon–nucleon interaction, as well as of its modifications occurring far from stability. Full article

(This article belongs to the Section Nuclear Theory and Experiments)

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21 pages, 590 KB

Open AccessEditor’s ChoiceArticle

Calculation of Energy and Angular Distributions of Electrons Produced in Intermediate-Energy p + H₂ Collisions

by Corey T. Plowman, Kade H. Spicer and Alisher S. Kadyrov

Atoms 2023, 11(8), 112; https://doi.org/10.3390/atoms11080112 - 14 Aug 2023

Cited by 4 | Viewed by 2036

Abstract

We extend the two-centre wave-packet convergent close-coupling approach to doubly differential ionisation in proton collisions with H₂ to intermediate projectile energies. The results for the doubly differential cross section at projectile energies from 48 to 200 keV are presented as a function [...] Read more.

We extend the two-centre wave-packet convergent close-coupling approach to doubly differential ionisation in proton collisions with H₂ to intermediate projectile energies. The results for the doubly differential cross section at projectile energies from 48 to 200 keV are presented as a function of the energy and angle of emitted electrons. We consider a wide range of emission angles from 10 to

160^{\circ}

, and compare our results to experimental data, where available. Excellent agreement between the presented results and the experimental data was found, especially for emission angles less than

130^{\circ}

. For very large backward emission angles our calculations tended to slightly overestimate the experimental data when energetic electrons are ejected and the doubly differential cross section is very small. This discrepancy may be due to the large uncertainties in the experimental data in this region and the model target description. Overall, the present results show significant improvement upon currently available theoretical results and provide a consistently accurate description of this process across a wide range of incident energies. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Atomic Collision and Atomic Spectroscopy)

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12 pages, 3988 KB

Open AccessEditor’s ChoiceArticle

Decay of Persistent Currents in Annular Atomic Superfluids

by Klejdja Xhani, Giulia Del Pace, Francesco Scazza and Giacomo Roati

Atoms 2023, 11(8), 109; https://doi.org/10.3390/atoms11080109 - 27 Jul 2023

Cited by 10 | Viewed by 2159

Abstract

We investigate the role of vortices in the decay of persistent current states of annular atomic superfluids by solving numerically the Gross–Pitaevskii equation, and we directly compare our results with the

^{6}

Li experiment at LENS data. We theoretically model the optical phase-imprinting [...] Read more.

We investigate the role of vortices in the decay of persistent current states of annular atomic superfluids by solving numerically the Gross–Pitaevskii equation, and we directly compare our results with the

^{6}

Li experiment at LENS data. We theoretically model the optical phase-imprinting technique employed to experimentally excite finite-circulation states in the Bose–Einstein condensation regime, accounting for imperfections of the optical gradient imprinting profile. By comparing simulations of this realistic protocol to an ideal imprinting, we show that the introduced density excitations arising from imperfect imprinting are mainly responsible for limiting the maximum reachable winding number

w_{\max}

in the superfluid ring. We also investigate the effect of a point-like obstacle with variable potential height

V_{0}

on the decay of circulating supercurrents. For a given obstacle height, a critical circulation

w_{c}

exists, such that for an initial circulation

w_{0}

larger than

w_{c}

the supercurrent decays through the emission of vortices, which cross the superflow and thus induce phase slippage. Higher values of the obstacle height

V_{0}

further favor the entrance of vortices, thus leading to lower values of

w_{c}

. Furthermore, the stronger vortex-defect interaction at higher

V_{0}

leads to vortices that propagate closer to the center of the ring condensate. The combination of both these effects leads to an increase in the supercurrent decay rate for increasing

w_{0}

, in agreement with experimental observations. Full article

(This article belongs to the Special Issue Recent Trends on Quantum Fluctuations in Ultra-Cold Quantum Gases)

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16 pages, 5924 KB

Open AccessEditor’s ChoiceArticle

Setup for the Ionic Lifetime Measurement of the ^229mTh³⁺ Nuclear Clock Isomer

by Kevin Scharl, Shiqian Ding, Georg Holthoff, Mahmood Irtiza Hussain, Sandro Kraemer, Lilli Löbell, Daniel Moritz, Tamila Rozibakieva, Benedict Seiferle, Florian Zacherl and Peter G. Thirolf

Atoms 2023, 11(7), 108; https://doi.org/10.3390/atoms11070108 - 24 Jul 2023

Cited by 5 | Viewed by 2781

Abstract

For the realization of an optical nuclear clock, the first isomeric excited state of thorium-229 (^229mTh) is currently the only candidate due to its exceptionally low-lying excitation energy (

8.338 \pm 0.024

eV). Such a nuclear clock holds promise not only [...] Read more.

For the realization of an optical nuclear clock, the first isomeric excited state of thorium-229 (^229mTh) is currently the only candidate due to its exceptionally low-lying excitation energy (

8.338 \pm 0.024

eV). Such a nuclear clock holds promise not only to be a very precise metrological device but also to extend the knowledge of fundamental physics studies, such as dark matter research or variations in fundamental constants. Considerable progress was achieved in recent years in characterizing ^229mTh from its first direct identification in 2016 to the only recent observation of the long-sought-after radiative decay channel. So far, nuclear resonance as the crucial parameter of a nuclear frequency standard has not yet been determined with laser-spectroscopic precision. To determine another yet unknown basic property of the thorium isomer and to further specify the linewidth of its ground-state transition, a measurement of the ionic lifetime of the isomer is in preparation. Theory and experimental investigations predict the lifetime to be 10³–10⁴ s. To precisely target this property using hyperfine structure spectroscopy, an experimental setup is currently being commissioned at LMU Munich. It is based on a cryogenic Paul trap providing long-enough storage times for ^229mTh ions, that will be sympathetically cooled with ⁸⁸Sr⁺. This article presents a concept for an ionic lifetime measurement and discusses the laser-optical part of a setup specifically developed for this purpose. Full article

(This article belongs to the Special Issue Over a Century of Nuclear Isomers: Challenges and Prospects)

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20 pages, 425 KB

Open AccessEditor’s ChoiceArticle

Exponentially Correlated Hylleraas–Configuration Interaction Studies of Atomic Systems. III. Upper and Lower Bounds to He-Sequence Oscillator Strengths for the Resonance ¹S→¹P Transition

by James S. Sims, Bholanath Padhy and María Belén Ruiz Ruiz

Atoms 2023, 11(7), 107; https://doi.org/10.3390/atoms11070107 - 22 Jul 2023

Cited by 1 | Viewed by 1950

Abstract

The exponentially correlated Hylleraas–configuration interaction method (E-Hy-CI) is a generalization of the Hylleraas–configuration interaction method (Hy-CI) in which the single

r_{i j}

of an Hy-CI wave function is generalized to a form of the generic type [...] Read more.

The exponentially correlated Hylleraas–configuration interaction method (E-Hy-CI) is a generalization of the Hylleraas–configuration interaction method (Hy-CI) in which the single

r_{i j}

of an Hy-CI wave function is generalized to a form of the generic type

r_{i j}^{ν_{i j}} e^{- ω_{i j} r_{i j}}

. This work continues the exploration, begun in the first two papers in this series (on the helium atom and on ground and excited

S

states of Li II), of whether wave functions containing both linear and exponential

r_{i j}

factors converge more rapidly than either one alone. In the present study, we examined not only 1

s^{2}

^{1} S

states but 1s2p

^{1} P

states for the He I, Li II, Be III, C V and O VII members of the He isoelectronic sequence as well. All

^{1} P

energies except He I are better than previous results. The wave functions obtained were used to calculate oscillator strengths, including upper and lower bounds, for the He-sequence lowest (resonance)

^{1} S \to

^{1} P

transition. Interpolation techniques were used to make a graphical study of the oscillator strength behavior along the isoelectronic sequence. Comparisons were made with previous experimental and theoretical results. The results of this study are oscillator strengths for the 1

s^{2}

^{1} S \to

1s2

p^{1} P

He isoelectronic sequence with rigorous non-relativistic quantum mechanical upper and lower bounds of (0.001–0.003)% and probable precision ≤ 0.0000003, and were obtained by extending the previously developed E-Hy-CI formalism to include the calculation of transition moments (oscillator strengths). Full article

(This article belongs to the Special Issue Recent Advances in Atomic and Molecular Spectroscopy)

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14 pages, 408 KB

Open AccessEditor’s ChoiceArticle

Mean-Field Description of Cooperative Scattering by Atomic Clouds

by Nicola Piovella

Atoms 2023, 11(7), 101; https://doi.org/10.3390/atoms11070101 - 29 Jun 2023

Viewed by 1615

Abstract

We present analytic expressions for the scattering of light by an extended atomic cloud. We obtain the solution for the mean-field excitation of different atomic spherical distributions driven by a uniform laser, including the initial build up, the steady state and the decay [...] Read more.

We present analytic expressions for the scattering of light by an extended atomic cloud. We obtain the solution for the mean-field excitation of different atomic spherical distributions driven by a uniform laser, including the initial build up, the steady state and the decay after the laser is switched off. We show that the mean-field model does not describe subradiant scattering due to the negative interference of the photons scattered by N discrete atoms. Full article

(This article belongs to the Section Cold Atoms, Quantum Gases and Bose-Einstein Condensation)

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21 pages, 9092 KB

Open AccessEditor’s ChoiceReview

Neutron Interferometer Experiments Studying Fundamental Features of Quantum Mechanics

by Armin Danner, Hartmut Lemmel, Richard Wagner, Stephan Sponar and Yuji Hasegawa

Atoms 2023, 11(6), 98; https://doi.org/10.3390/atoms11060098 - 15 Jun 2023

Cited by 5 | Viewed by 2729

Abstract

Quantum theory provides us with the best account of microscopic components of matter as well as of radiation. It was introduced in the twentieth century and has experienced a wide range of success. Although the theory’s probabilistic predictions of final experimental outcomes is [...] Read more.

Quantum theory provides us with the best account of microscopic components of matter as well as of radiation. It was introduced in the twentieth century and has experienced a wide range of success. Although the theory’s probabilistic predictions of final experimental outcomes is found to be correct with high precision, there is no general consensus regarding what is actually going on with a quantum system “en route”, or rather the perceivable intermediate behavior of a quantum system, e.g., the particle’s behavior in the double-slit experiment. Neutron interferometry using single silicon perfect crystals is established as a versatile tool to test fundamental phenomena in quantum mechanics, where an incident neutron beam is coherently split in two or three beam paths with macroscopic separation of several centimeters. Here, we present quantum optical experiments with these matter-wave interferometers, studying the effect of the quantum Cheshire Cat in some variants, the neutron’s presence in the paths of the interferometer as well as the direct test of a commutation relation. To reduce disturbances induced by the measurement, the interaction strength is lessened and so-called weak interactions are exploited by employing pre- and post-selection procedures. All results of the experiments confirm the predictions of quantum theory; the observed behaviors of the neutron between the pre- and post-selection in space and time emphasize striking and counter-intuitive aspects of quantum theory. Full article

(This article belongs to the Special Issue Advances in and Prospects for Matter Wave Interferometry)

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11 pages, 3248 KB

Open AccessEditor’s ChoiceArticle

Pulse Cycle Dependent Nondipole Effects in Above-Threshold Ionization

by Danish Furekh Dar and Stephan Fritzsche

Atoms 2023, 11(6), 97; https://doi.org/10.3390/atoms11060097 - 12 Jun 2023

Viewed by 1876

Abstract

In this study, we employ strong field approximation (SFA) to investigate the influence of the number of pulse cycles on above-threshold ionization within the framework of nondipole theory. The SFA enables the analysis of the ionization process under the dominance of the electric [...] Read more.

In this study, we employ strong field approximation (SFA) to investigate the influence of the number of pulse cycles on above-threshold ionization within the framework of nondipole theory. The SFA enables the analysis of the ionization process under the dominance of the electric field, compared to other factors such as the binding potential of an atom. Nondipole effects, including higher-order multipole fields, can significantly impact ionization dynamics. However, the interaction between nondipole effects and pulse cycles remains unclear. Therefore, we investigate the pulse cycle dependence of ionization and examine peak shifts in Kr and Ar atoms. Our findings have implications for comprehensively understanding the effects of electromagnetic fields on electron behavior. The insights gained from this study provide valuable guidance for future research in strong field ionization. Full article

(This article belongs to the Special Issue Recent Progress in Strong-Field Atomic and Molecular Physics)

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14 pages, 5827 KB

Open AccessEditor’s ChoiceArticle

Improved Line Intensity Analysis of Neutral Helium by Incorporating the Reabsorption Processes in a Helium Collisional-Radiative Model

by Keren Lin, Motoshi Goto and Hiroshi Akatsuka

Atoms 2023, 11(6), 94; https://doi.org/10.3390/atoms11060094 - 8 Jun 2023

Cited by 4 | Viewed by 2024

Abstract

In this study, eight emission lines in the visible wavelength range of neutral helium were used to diagnose the electron density and temperature of the Large Helical Device (LHD) helium plasma instead of the conventional three-line method. The collisional-radiative (CR) model for low-pressure [...] Read more.

In this study, eight emission lines in the visible wavelength range of neutral helium were used to diagnose the electron density and temperature of the Large Helical Device (LHD) helium plasma instead of the conventional three-line method. The collisional-radiative (CR) model for low-pressure helium plasma was revised to include the optical escape factors for spontaneous transition from the n¹P states to the ground state so that the influence of the absorption effect under optically thick conditions could be considered. The developed algorithm was based on fitting the number densities of eight excited states obtained using optical emission spectroscopy (OES). The electron density, electron temperature, ground-state density, and optical escape factors were selected as the fitting parameters. The objective function was set as the summation of the residual errors between the number densities measured in the experiment and those calculated using the revised model. A regularization term was introduced for the optical escape factor and optimized through bias and variance analyses. The results show that the agreement between the number density calculated by the algorithm and its counterpart measured in the experiment was generally improved compared to the method using three lines. Full article

(This article belongs to the Special Issue Plasma Spectroscopy and Plasma Diagnostics: From Classical to Sophisticated Methods)

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33 pages, 484 KB

Open AccessEditor’s ChoiceReview

Atomic Lifetimes of Astrophysical Interest in Ions of Fe

by Elmar Träbert

Atoms 2023, 11(5), 85; https://doi.org/10.3390/atoms11050085 - 22 May 2023

Cited by 3 | Viewed by 2526

Abstract

Multiply charged ions of iron dominate the EUV spectrum of the solar corona. For the interpretation of such spectra, data on both the atomic structure and the transition rate are essential, most of which are provided by theory and computation. The wavelengths of [...] Read more.

Multiply charged ions of iron dominate the EUV spectrum of the solar corona. For the interpretation of such spectra, data on both the atomic structure and the transition rate are essential, most of which are provided by theory and computation. The wavelengths of observed spectra are used to test the predicted energy level structure, while the line intensities depend on level lifetimes and branch fractions. A number of electric dipole and higher-order transition rates have been measured over the years in the laboratory, mostly by beam-foil spectroscopy, at heavy-ion storage rings, and at various ion traps. In this paper, the state of the knowledge base on level lifetimes in all ions of Fe is assessed, and the problems of further progress are outlined. Full article

(This article belongs to the Special Issue Atomic and Molecular Data in Astronomy and Astrophysics)

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15 pages, 736 KB

Open AccessEditor’s ChoiceArticle

Collision Strengths of Astrophysical Interest for Multiply Charged Ions

by Stephan Fritzsche, Li-Guang Jiao, Yuan-Cheng Wang and Jozef E. Sienkiewicz

Atoms 2023, 11(5), 80; https://doi.org/10.3390/atoms11050080 - 6 May 2023

Cited by 9 | Viewed by 2425

Abstract

The electron impact excitation and ionization processes are crucial for modeling the spectra of different astrophysical objects, from atmospheres of late-type stars to remnants of supernovae and up to the light emission from neutron star mergers, to name just a few. Despite their [...] Read more.

The electron impact excitation and ionization processes are crucial for modeling the spectra of different astrophysical objects, from atmospheres of late-type stars to remnants of supernovae and up to the light emission from neutron star mergers, to name just a few. Despite their significance, however, little is known quantitatively about these processes for low- and medium-impact energies of, say,

E_{kin} ≲ 5000

eV of the free incident electron. To further explore the role of impact excitation, we here expanded Jac, the Jena Atomic Calculator, to the computation of distorted wave collision strengths for fine-structure-resolved, as well as configuration-averaged transitions. While we excluded the formation of dielectronic resonances, these tools can be readily applied for ions with a complex shell structure and by including the major relativistic contributions to these strengths. Detailed computations of the collision strengths are shown and explained for the impact excitation of lithium- and chlorine-like ions. When compared with other, well-correlated methods, good agreement was found, and hence, these tools will support studies of effective collision strengths for a wide range of electron impact energies, levels, and ionic charge states. Full article

(This article belongs to the Special Issue Atomic Processes for Plasma Modeling Applications)

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369 pages, 1459 KB

Open AccessEditor’s ChoiceArticle

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 - 5 Apr 2023

Cited by 45 | Viewed by 5933

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 KB

Open AccessFeature PaperEditor’s ChoiceArticle

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 - 1 Apr 2023

Cited by 10 | Viewed by 2850

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

3 d^{7} a^{4} F_{9 / 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 KB

Open AccessEditor’s ChoiceArticle

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 4 | Viewed by 2638

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 KB

Open AccessEditor’s ChoiceReview

Photoionization and Electron–Ion Recombination in Astrophysical Plasmas

by D. John Hillier

Atoms 2023, 11(3), 54; https://doi.org/10.3390/atoms11030054 - 9 Mar 2023

Cited by 6 | Viewed by 3141

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 KB

Open AccessEditor’s ChoiceArticle

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 12 | Viewed by 2797

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

20 ℏ k

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 KB

Open AccessEditor’s ChoiceArticle

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 - 2 Feb 2023

Cited by 3 | Viewed by 2267

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 KB

Open AccessEditor’s ChoiceArticle

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 11 | Viewed by 2842

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 KB

Open AccessEditor’s ChoiceArticle

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 2407

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 KB

Open AccessEditor’s ChoiceArticle

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 49 | Viewed by 6490

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 KB

Open AccessEditor’s ChoiceArticle

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 7 | Viewed by 2168

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

E 1

-allowed intercombination transition at 244.909 Å, the other an

E 1

-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

E 1

-allowed intercombination transition at 244.909 Å, the other an

E 1

-forbidden

M 2

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 KB

Open AccessEditor’s ChoiceArticle

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 - 7 Sep 2022

Cited by 12 | Viewed by 2946

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

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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21 pages, 2374 KB

Open AccessEditor’s ChoiceReview

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 2462

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

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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8 pages, 2046 KB

Open AccessEditor’s ChoiceArticle

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 - 1 Jun 2022

Cited by 11 | Viewed by 3550

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 KB

Open AccessEditor’s ChoiceReview

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 53 | Viewed by 6628

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 KB

Open AccessEditor’s ChoiceArticle

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 - 9 May 2022

Cited by 8 | Viewed by 2943

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 7s

^{2}

, 6d

^{1}

7s

^{1}

and 7s

^{1}

7p

^{1}

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 KB

Open AccessEditor’s ChoiceArticle

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 11 | Viewed by 5925

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 \pm 0.2 \times 10^{7}

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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Graphical abstract

10 pages, 1125 KB

Open AccessEditor’s ChoiceArticle

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 - 2 Mar 2022

Cited by 8 | Viewed by 4591

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 KB

Open AccessEditor’s ChoiceArticle

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 13 | Viewed by 4128

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 KB

Open AccessEditor’s ChoiceArticle

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 - 7 Feb 2022

Cited by 12 | Viewed by 3164

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 KB

Open AccessEditor’s ChoiceArticle

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 13 | Viewed by 4236

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 Th

^{2 +}

ions with a

5 f 6 d

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 KB

Open AccessEditor’s ChoiceArticle

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 11 | Viewed by 3508

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 KB

Open AccessEditor’s ChoiceArticle

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 20 | Viewed by 5360

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 I

_{2}

. 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 I

_{2}

. 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 I

_{2}

using the BEB model. Full article

(This article belongs to the Special Issue A Tribute to Oleg Zatsarinny (1953–2021) and His Science–Fees Are Waived)

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14 pages, 3598 KB

Open AccessEditor’s ChoiceArticle

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 3196

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

(This article belongs to the Special Issue Electron Scattering in Gases –from Cross Sections to Plasma Modeling)

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10 pages, 471 KB

Open AccessEditor’s ChoiceArticle

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 8 | Viewed by 2924

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 SF

_{6}

/O

_{2}

plasma. Full article

(This article belongs to the Special Issue Electron Scattering in Gases –from Cross Sections to Plasma Modeling)

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12 pages, 1593 KB

Open AccessEditor’s ChoiceReview

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 - 7 Oct 2021

Cited by 11 | Viewed by 3911

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

(This article belongs to the Special Issue Electron Scattering in Gases –from Cross Sections to Plasma Modeling)

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8 pages, 1738 KB

Open AccessEditor’s ChoiceArticle

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 16 | Viewed by 2938

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

(This article belongs to the Special Issue A Tribute to Oleg Zatsarinny (1953–2021) and His Science–Fees Are Waived)

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11 pages, 2406 KB

Open AccessEditor’s ChoiceArticle

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 - 6 Sep 2021

Cited by 9 | Viewed by 3228

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

(This article belongs to the Special Issue Electron Scattering in Gases –from Cross Sections to Plasma Modeling)

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19 pages, 3238 KB

Open AccessEditor’s ChoiceArticle

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 - 4 Aug 2021

Cited by 12 | Viewed by 2977

Abstract

We report new accurate measurements of the drift mobility

μ

of quasifree electrons in moderately dense helium gas in the temperature range

26 K \leq T \leq 300 K

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

26 K \leq T \leq 300 K

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

μ_{0} N

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

μ_{0} N

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

μ_{0} N

as a function of N at intermediate densities. Full article

(This article belongs to the Special Issue Electron Scattering in Gases –from Cross Sections to Plasma Modeling)

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14 pages, 763 KB

Open AccessEditor’s ChoiceArticle

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 6 | Viewed by 2943

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

(This article belongs to the Special Issue A Tribute to Oleg Zatsarinny (1953–2021) and His Science–Fees Are Waived)

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37 pages, 4365 KB

Open AccessEditor’s ChoiceArticle

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 12 | Viewed by 4904

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 KB

Open AccessEditor’s ChoiceArticle

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 28 | Viewed by 4520

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 KB

Open AccessEditor’s ChoiceArticle

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 - 9 Jun 2021

Cited by 9 | Viewed by 3054

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

(This article belongs to the Special Issue Electron Scattering in Gases –from Cross Sections to Plasma Modeling)

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32 pages, 903 KB

Open AccessEditor’s ChoiceReview

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 9 | Viewed by 4208

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 KB

Open AccessFeature PaperEditor’s ChoiceArticle

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 5 | Viewed by 4049

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

\frac{2 π}{T}

. This system exhibits the hallmark signature of a DTC—persistent sub-harmonic oscillations with frequency

\frac{π}{T}

—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,

J T = 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

J T = 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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