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Journal Cover   Atoms
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  This is an Open Access Journal Open Access journal
   ISSN (Online) 2218-2004
   Published by MDPI Homepage  [140 journals]
  • Atoms, Vol. 3, Pages 273-298: Spectra of W VIII and W IX in the EUV Region

    • Pages: 273 - 298
      Abstract: The results obtained on the W VIII spectrum as well as on the isoelectronic spectra Lu V, Hf VI, Ta VII, and Re IX in the VUV wavelength region are summarized with emphasis on the main trends along the isoelectronic sequence. A total of 187 lines of W VIII in the region of 160–271 Å were accurately measured and identified, 98 levels were found, and transition probabilities calculated. The isoelectronic regularities support the data on W VIII. A list of spectral lines in the region of 170–199 Å, considered as belonging to W IX, is presented.
      PubDate: 2015-06-30
      DOI: 10.3390/atoms3030273
      Issue No: Vol. 3, No. 3 (2015)
  • Atoms, Vol. 3, Pages 299-319: Detailed Analysis of Configuration
           Interaction and Calculation of Radiative Transition Rates in Seven Times
           Ionized Tungsten (W VIII)

    • Pages: 299 - 319
      Abstract: A new set of oscillator strengths and transition probabilities for EUV spectral lines of seven times ionized tungsten (W VIII) is reported in the present paper. These results have been obtained using the pseudo-relativistic Hartree-Fock (HFR) method combined with a semi-empirical optimization of the radial parameters minimizing the discrepancies between computed energy levels and available experimental data. The final physical model considered in the calculations has been chosen further to a detailed investigation of the configuration interaction in this atomic system characterized by complex configurations of the type 4f145s25p5, 4f145s25p4nl, 4f145s5p6, 4f135s25p6, 4f135s25p5nl and 4f125s25p6nl (nl = 5d, 6s).
      PubDate: 2015-06-30
      DOI: 10.3390/atoms3030299
      Issue No: Vol. 3, No. 3 (2015)
  • Atoms, Vol. 3, Pages 320-338: On the Classical Coupling between Gravity
           and Electromagnetism

    • Authors: Maria Becker, Adam Caprez, Herman Batelaan
      Pages: 320 - 338
      Abstract: Coupling between electromagnetism and gravity, manifested as the distorted Coulomb field of a charge distribution in a gravitational field, has never been observed. A physical system consisting of an electron in a charged shell provides a coupling that is orders of magnitude stronger than for any previously-considered system. A shell voltage of one megavolt is required to establish a gravitationally-induced electromagnetic force equal in magnitude to the force of gravity on an electron. The experimental feasibility of detecting these forces on an electron is discussed. The effect establishes a relation between Einstein’s energy-mass equivalence and the coupling between electromagnetism and gravity.
      PubDate: 2015-06-30
      DOI: 10.3390/atoms3030320
      Issue No: Vol. 3, No. 3 (2015)
  • Atoms, Vol. 3, Pages 339-347: Influence of Virtual Photon Process on the
           Generation of Squeezed Light from Atoms in an Optical Cavity

    • Authors: Aranya Bhattacherjee
      Pages: 339 - 347
      Abstract: We show that a collection of two-level atoms in an optical cavity beyond the rotating wave approximation and in the dispersive-adiabatic and non-dispersive adiabatic regime constitutes a nonlinear medium and is capable of generating squeezed state of light. It is found that squeezing produced in the non-dispersive adiabatic regime is significantly high compared to that produced in the dispersive-adiabatic limit. On the other hand, we also show that it could be possible to observe the Dicke superradiant quantum phase transition in the dispersive-adiabatic regime where the Ã2 term is negligible. Such a system can be an essential component of a larger quantum-communication system.
      PubDate: 2015-07-24
      DOI: 10.3390/atoms3030339
      Issue No: Vol. 3, No. 3 (2015)
  • Atoms, Vol. 3, Pages 348-366: Cavity-Assisted Generation of Sustainable
           Macroscopic Entanglement of Ultracold Gases

    • Authors: Chaitanya Joshi, Jonas Larson
      Pages: 348 - 366
      Abstract: Prospects for reaching persistent entanglement between two spatially-separated atomic Bose–Einstein condensates are outlined. The system setup comprises two condensates loaded in an optical lattice, which, in return, is confined within a high-Q optical resonator. The system is driven by an external laser that illuminates the atoms, such that photons can scatter into the cavity. In the superradiant phase, a cavity field is established, and we show that the emerging cavity-mediated interactions between the two condensates is capable of entangling them despite photon losses. This macroscopic atomic entanglement is sustained throughout the time-evolution apart from occasions of sudden deaths/births. Using an auxiliary photon mode and coupling it to a collective quadrature of the two condensates, we demonstrate that the auxiliary mode’s squeezing is proportional to the atomic entanglement, and as such, it can serve as a probe field of the macroscopic entanglement.
      PubDate: 2015-08-04
      DOI: 10.3390/atoms3030348
      Issue No: Vol. 3, No. 3 (2015)
  • Atoms, Vol. 3, Pages 367-391: Experiments with Highly-Ionized Atoms in
           Unitary Penning Traps

    • Authors: Shannon Hoogerheide, Aung Naing, Joan Dreiling, Samuel Brewer, Nicholas Guise, Joseph Tan
      Pages: 367 - 391
      Abstract: Highly-ionized atoms with special properties have been proposed for interesting applications, including potential candidates for a new generation of optical atomic clocks at the one part in 1019 level of precision, quantum information processing and tests of fundamental theory. The proposed atomic systems are largely unexplored. Recent developments at NIST are described, including the isolation of highly-ionized atoms at low energy in unitary Penning traps and the use of these traps for the precise measurement of radiative decay lifetimes (demonstrated with a forbidden transition in Kr17+), as well as for studying electron capture processes.
      PubDate: 2015-08-14
      DOI: 10.3390/atoms3030367
      Issue No: Vol. 3, No. 3 (2015)
  • Atoms, Vol. 3, Pages 392-406: Probing and Manipulating Fermionic and
           Bosonic Quantum Gases with Quantum Light

    • Pages: 392 - 406
      Abstract: We study the atom-light interaction in the fully quantum regime, with the focus on off-resonant light scattering into a cavity from ultracold atoms trapped in an optical lattice. The detection of photons allows the quantum nondemolition (QND) measurement of quantum correlations of the atomic ensemble, distinguishing between different quantum states. We analyse the entanglement between light and matter and show how it can be exploited for realising multimode macroscopic quantum superpositions, such as Schrödinger cat states, for both bosons and fermions. We provide examples utilising different measurement schemes and study their robustness to decoherence. Finally, we address the regime where the optical lattice potential is a quantum dynamical variable and is modified by the atomic state, leading to novel quantum phases and significantly altering the phase diagram of the atomic system.
      PubDate: 2015-09-02
      DOI: 10.3390/atoms3030392
      Issue No: Vol. 3, No. 3 (2015)
  • Atoms, Vol. 3, Pages 407-421: Extreme Ultraviolet Spectra of Few-Times
           Ionized Tungsten for Divertor Plasma Diagnostics

    • Authors: Joel Clementson, Thomas Lennartsson, Peter Beiersdorfer
      Pages: 407 - 421
      Abstract: The extreme ultraviolet (EUV) emission from few-times ionized tungsten atoms has been experimentally studied at the Livermore electron beam ion trap facility. The ions were produced and confined during low-energy operations of the EBIT-I electron beam ion trap. By varying the electron-beam energy from around 30–300 eV, tungsten ions in charge states expected to be abundant in tokamak divertor plasmas were excited, and the resulting EUV emission was studied using a survey spectrometer covering 120–320 Å. It is found that the emission strongly depends on the excitation energy; below 150 eV, it is relatively simple, consisting of strong isolated lines from a few charge states, whereas at higher energies, it becomes very complex. For divertor plasmas with tungsten impurity ions, this emission should prove useful for diagnostics of tungsten flux rates and charge balance, as well as for radiative cooling of the divertor volume. Several lines in the 194–223 Å interval belonging to the spectra of five- and seven-times ionized tungsten (Tm-like W VI and Ho-like W VIII) were also measured using a high-resolution spectrometer.
      PubDate: 2015-09-09
      DOI: 10.3390/atoms3030407
      Issue No: Vol. 3, No. 3 (2015)
  • Atoms, Vol. 3, Pages 422-432: Quantum Entanglement and Shannon Information
           Entropy for the Doubly Excited Resonance State in Positronium Negative Ion

    • Authors: Chien-Hao Lin, Yew Ho
      Pages: 422 - 432
      Abstract: In the present work, we report an investigation on quantum entanglement in the doubly excited 2s2 1Se resonance state of the positronium negative ion by using highly correlated Hylleraas type wave functions, determined by calculation of the density of resonance states with the stabilization method. Once the resonance wave function is obtained, the spatial (electron-electron orbital) entanglement entropies (von Neumann and linear) can be quantified using the Schmidt decomposition method. Furthermore, Shannon entropy in position space, a measure for localization (or delocalization) for such a doubly excited state, is also calculated.
      PubDate: 2015-09-21
      DOI: 10.3390/atoms3030422
      Issue No: Vol. 3, No. 3 (2015)
  • Atoms, Vol. 3, Pages 433-449: A Realization of a Quasi-Random Walk for
           Atoms in Time-Dependent Optical Potentials

    • Authors: Torsten Hinkel, Helmut Ritsch, Claudiu Genes
      Pages: 433 - 449
      Abstract: We consider the time dependent dynamics of an atom in a two-color pumped cavity, longitudinally through a side mirror and transversally via direct driving of the atomic dipole. The beating of the two driving frequencies leads to a time dependent effective optical potential that forces the atom into a non-trivial motion, strongly resembling a discrete random walk behavior between lattice sites. We provide both numerical and analytical analysis of such a quasi-random walk behavior.
      PubDate: 2015-09-23
      DOI: 10.3390/atoms3030433
      Issue No: Vol. 3, No. 3 (2015)
  • Atoms, Vol. 3, Pages 450-473: Cavity Quantum Electrodynamics of
           Continuously Monitored Bose-Condensed Atoms

    • Authors: Mark Lee, Janne Ruostekoski
      Pages: 450 - 473
      Abstract: We study cavity quantum electrodynamics of Bose-condensed atoms that are subjected to continuous monitoring of the light leaking out of the cavity. Due to a given detection record of each stochastic realization, individual runs spontaneously break the symmetry of the spatial profile of the atom cloud and this symmetry can be restored by considering ensemble averages over many realizations. We show that the cavity optomechanical excitations of the condensate can be engineered to target specific collective modes. This is achieved by exploiting the spatial structure and symmetries of the collective modes and light fields. The cavity fields can be utilized both for strong driving of the collective modes and for their measurement. In the weak excitation limit the condensate–cavity system may be employed as a sensitive phonon detector which operates by counting photons outside the cavity that have been selectively scattered by desired phonons.
      PubDate: 2015-09-23
      DOI: 10.3390/atoms3030450
      Issue No: Vol. 3, No. 3 (2015)
  • Atoms, Vol. 3, Pages 53-75: Fully Relativistic Electron Impact Excitation
           Cross-Section and Polarization for Tungsten Ions

    • Authors: Priti, Dipti, Lalita Sharma, Rajesh Srivastava
      Pages: 53 - 75
      Abstract: Electron impact excitation of highly charged tungsten ions in the framework of a fully relativistic distorted wave approach is considered in this paper. Calculations of electron impact excitation cross-sections for the M- and L-shell transitions in the tungsten ions Wn+ (n = 44–66) and polarization of the decay of photons from the excited tungsten ions are briefly reviewed and discussed. New calculations in the wide range of incident electron energies are presented for M-shell transitions in the K-like through Ne-like tungsten ions.
      PubDate: 2015-04-28
      DOI: 10.3390/atoms3020053
      Issue No: Vol. 3, No. 2 (2015)
  • Atoms, Vol. 3, Pages 76-85: Collisional-Radiative Modeling of Tungsten at
           Temperatures of 1200–2400 eV

    • Authors: James Colgan, Christopher Fontes, Honglin Zhang, Joseph Abdallah
      Pages: 76 - 85
      Abstract: We discuss new collisional-radiative modeling calculations of tungsten at moderate temperatures of 1200 to 2400 eV. Such plasma conditions are relevant to ongoing experimental work at ASDEX Upgrade and are expected to be relevant for ITER. Our calculations are made using the Los Alamos National Laboratory (LANL) collisional-radiative modeling ATOMIC code. These calculations formed part of a submission to the recent NLTE-8 workshop that was held in November 2013. This series of workshops provides a forum for detailed comparison of plasma and spectral quantities from NLTE collisional-radiative modeling codes. We focus on the LANL ATOMIC calculations for tungsten that were submitted to the NLTE-8 workshop and discuss different models that were constructed to predict the tungsten emission. In particular, we discuss comparisons between semi-relativistic configuration-average and fully relativistic configuration-average calculations. We also present semi-relativistic calculations that include fine-structure detail, and discuss the difficult problem of ensuring completeness with respect to the number of configurations included in a CR calculation.
      PubDate: 2015-04-30
      DOI: 10.3390/atoms3020076
      Issue No: Vol. 3, No. 2 (2015)
  • Atoms, Vol. 3, Pages 86-119: Radiative Recombination and Photoionization
           Data for Tungsten Ions. Electron Structure of Ions in Plasmas

    • Authors: Malvina Trzhaskovskaya, Vladimir Nikulin
      Pages: 86 - 119
      Abstract: Theoretical studies of tungsten ions in plasmas are presented. New calculations of the radiative recombination and photoionization cross-sections, as well as radiative recombination and radiated power loss rate coefficients have been performed for 54 tungsten ions for the range W6+–W71+. The data are of importance for fusion investigations at the reactor ITER, as well as devices ASDEX Upgrade and EBIT. Calculations are fully relativistic. Electron wave functions are found by the Dirac–Fock method with proper consideration of the electron exchange. All significant multipoles of the radiative field are taken into account. The radiative recombination rates and the radiated power loss rates are determined provided the continuum electron velocity is described by the relativistic Maxwell–Jüttner distribution. The impact of the core electron polarization on the radiative recombination cross-section is estimated for the Ne-like iron ion and for highly-charged tungsten ions within an analytical approximation using the Dirac–Fock electron wave functions. The effect is shown to enhance the radiative recombination cross-sections by ≲20%. The enhancement depends on the photon energy, the principal quantum number of polarized shells and the ion charge. The influence of plasma temperature and density on the electron structure of ions in local thermodynamic equilibrium plasmas is investigated. Results for the iron and uranium ions in dense plasmas are in good agreement with previous calculations. New calculations were performed for the tungsten ion in dense plasmas on the basis of the average-atom model, as well as for the impurity tungsten ion in fusion plasmas using the non-linear self-consistent field screening model. The temperature and density dependence of the ion charge, level energies and populations are considered.
      PubDate: 2015-05-18
      DOI: 10.3390/atoms3020086
      Issue No: Vol. 3, No. 2 (2015)
  • Atoms, Vol. 3, Pages 120-161: Fusion-Related Ionization and Recombination
           Data for Tungsten Ions in Low to Moderately High Charge States

    • Pages: 120 - 161
      Abstract: Collisional processes and details of atomic structure of heavy many-electron atoms and ions are not yet understood in a fully satisfying manner. Experimental studies are required for guiding new theoretical approaches. In response to fusion-related needs for collisional and spectroscopic data on tungsten atoms in all charge states, a project has been initiated in which electron-impact and photon-induced ionization as well as photorecombination of Wq+ ions are studied. Cross sections and rate coefficients were determined for charge states q ranging from q = 1 to q = 5 for photoionization, for q = 1 up to q = 19 for electron-impact ionization and for q = 18 to q = 21 for electron-ion recombination. An overview, together with a critical assessment of the methods and results is provided.
      PubDate: 2015-05-20
      DOI: 10.3390/atoms3020120
      Issue No: Vol. 3, No. 2 (2015)
  • Atoms, Vol. 3, Pages 162-181: Tungsten Ions in Plasmas: Statistical Theory
           of Radiative-Collisional Processes

    • Authors: Alexander Demura, Mikhail Kadomtsev, Valery Lisitsa, Vladimir Shurygin
      Pages: 162 - 181
      Abstract: The statistical model for calculations of the collisional-radiative processes in plasmas with tungsten impurity was developed. The electron structure of tungsten multielectron ions is considered in terms of both the Thomas-Fermi model and the Brandt-Lundquist model of collective oscillations of atomic electron density. The excitation or ionization of atomic electrons by plasma electron impacts are represented as photo-processes under the action of flux of equivalent photons introduced by E. Fermi. The total electron impact single ionization cross-sections of ions Wk+ with respective rates have been calculated and compared with the available experimental and modeling data (e.g., CADW). Plasma radiative losses on tungsten impurity were also calculated in a wide range of electron temperatures 1 eV–20 keV. The numerical code TFATOM was developed for calculations of radiative-collisional processes involving tungsten ions. The needed computational resources for TFATOM code are orders of magnitudes less than for the other conventional numerical codes. The transition from corona to Boltzmann limit was investigated in detail. The results of statistical approach have been tested by comparison with the vast experimental and conventional code data for a set of ions Wk+. It is shown that the universal statistical model accuracy for the ionization cross-sections and radiation losses is within the data scattering of significantly more complex quantum numerical codes, using different approximations for the calculation of atomic structure and the electronic cross-sections.
      PubDate: 2015-05-25
      DOI: 10.3390/atoms3020162
      Issue No: Vol. 3, No. 2 (2015)
  • Atoms, Vol. 3, Pages 182-194: Photon-Induced Spin-Orbit Coupling in
           Ultracold Atoms inside Optical Cavity

    • Authors: Lin Dong, Chuanzhou Zhu, Han Pu
      Pages: 182 - 194
      Abstract: We consider an atom inside a ring cavity, where a plane-wave cavity field together with an external coherent laser beam induces a two-photon Raman transition between two hyperfine ground states of the atom. This cavity-assisted Raman transition induces effective coupling between atom’s internal degrees of freedom and its center-of-mass motion. In the meantime, atomic dynamics exerts a back-action to cavity photons. We investigate the properties of this system by adopting a mean-field and a full quantum approach, and show that the interplay between the atomic dynamics and the cavity field gives rise to intriguing nonlinear phenomena.
      PubDate: 2015-05-26
      DOI: 10.3390/atoms3020182
      Issue No: Vol. 3, No. 2 (2015)
  • Atoms, Vol. 3, Pages 195-259: MCDHF Calculations and Beam-Foil EUV Spectra
           of Boron-Like Sodium Ions (Na VII)

    • Pages: 195 - 259
      Abstract: Atomic data, such as wavelengths and line identifications, are necessary for many applications, especially in plasma diagnostics and for interpreting the spectra of distant astrophysical objects. The number of valence shell electrons increases the complexity of the computational problem. We have selected a five-electron ion, Na6+ (with the boron-like spectrum Na VII), for looking into the interplay of measurement and calculation. We summarize the available experimental work, perform our own extensive relativistic configuration interaction (RCI) computations based on multi-configuration Dirac–Hartree–Fock (MCDHF) wave functions, and compare the results to what is known of the level structure. We then discuss problems with databases that have begun to combine observations and computations.
      PubDate: 2015-06-09
      DOI: 10.3390/atoms3020195
      Issue No: Vol. 3, No. 2 (2015)
  • Atoms, Vol. 3, Pages 260-272: Tungsten Data for Current and Future Uses in
           Fusion and Plasma Science

    • Authors: Peter Beiersdorfer, Joel Clementson, Ulyana Safronova
      Pages: 260 - 272
      Abstract: We give a brief overview of our recent experimental and theoretical work involving highly charged tungsten ions in high-temperature magnetically confined plasmas. Our work includes X-ray and extreme ultraviolet spectroscopy, state-of-the-art structure calculations, the generation of dielectronic recombination rate coefficients, collisional-radiative spectral modeling and assessments of the atomic data need for X-ray diagnostics monitoring of the parameters of the core plasma of future tokamaks, such as ITER. We give examples of our recent results in these areas.
      PubDate: 2015-06-15
      DOI: 10.3390/atoms3020260
      Issue No: Vol. 3, No. 2 (2015)
  • Atoms, Vol. 3, Pages 1: Acknowledgement to Reviewers of Atoms in 2014

    • Authors: Atoms Office
      Pages: 1 - 1
      Abstract: The editors of Atoms would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2014:[...]
      PubDate: 2015-01-09
      DOI: 10.3390/atoms3010001
      Issue No: Vol. 3, No. 1 (2015)
  • Atoms, Vol. 3, Pages 2-52: Ab-Initio Calculations of Level Energies,
           Oscillator Strengths and Radiative Rates for E1 Transitions in
           Beryllium-Like Iron

    • Pages: 2 - 52
      Abstract: In the present work, energy levels, oscillator strengths, radiative rates and wavelengths of Be-like iron (Fe\(^{22+}\)) from ab-initio calculations using the multiconfiguration Dirac-Hartree-Fock method are presented. These quantities have been calculated for a set of configurations in the general form \(1s^2\,nl\,n'l'\) where \(n=2,3\) and \(\,n'=2,3,4,5\) and \(l=s,p,d\) and \(\,l'=s, p, d, f, g\). In addition, excitations of up to four electrons, including core-electron excitations, have been considered to improve the quality of the wave functions. This study comprises an extensive set of E1 transition rates between states with different \(J\). The present results are compared with the available experimental and theoretical data.
      PubDate: 2015-01-20
      DOI: 10.3390/atoms3010002
      Issue No: Vol. 3, No. 1 (2015)
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