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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. 4, Pages 12: Obtaining Atomic Matrix Elements from Vector
           Tune-Out Wavelengths Using Atom Interferometry

    • Authors: Adam Fallon, Charles Sackett
      First page: 12
      Abstract: Accurate values for atomic dipole matrix elements are useful in many areas of physics, and in particular for interpreting experiments such as atomic parity violation. Obtaining accurate matrix element values is a challenge for both experiment and theory. A new technique that can be applied to this problem is tune-out spectroscopy, which is the measurement of light wavelengths where the electric polarizability of an atom has a zero. Using atom interferometry methods, tune-out wavelengths can be measured very accurately. Their values depend on the ratios of various dipole matrix elements and are thus useful for constraining theory and broadening the application of experimental values. To date, tune-out wavelength measurements have focused on zeros of the scalar polarizability, but in general the vector polarizability also contributes. We show here that combined measurements of the vector and scalar polarizabilities can provide more detailed information about the matrix element ratios, and in particular can distinguish small contributions from the atomic core and the valence tail states. These small contributions are the leading error sources in current parity violation calculations for cesium.
      PubDate: 2016-03-30
      DOI: 10.3390/atoms4020012
      Issue No: Vol. 4, No. 2 (2016)
  • Atoms, Vol. 4, Pages 13: Multi-Configuration
           Dirac–Hartree–Fock (MCDHF) Calculations for B-Like Ions

    • Authors: Indu Khatri, Arun Goyal, Avnindra Singh, Man Mohan
      First page: 13
      Abstract: Relativistic configuration interaction results are presented for several B-like ions (Ge XXVIII, Rb XXXIII, Sr XXXIV, Ru XL, Sn XLVI, and Ba LII) using the multi-configuration Dirac–Hartree–Fock (MCDHF) method. The calculations are carried out in the active space approximation with the inclusion of the Breit interaction, the finite nuclear size effect, and quantum electrodynamic corrections. Results for fine structure energy levels for 1s22s22p and 2s2p2 configurations relative to the ground state are reported. The transition wavelengths, transition probabilities, line strengths, and absorption oscillator strengths for 2s22p–2s2p2 electric dipole (E1) transitions are calculated. Both valence and core-valence correlation effects were accounted for through single-double multireference (SD-MR) expansions to increasing sets of active orbitals. Comparisons are made with the available data and good agreement is achieved. The values calculated using core–valence correlation are found to be very close to other theoretical and experimental values. The behavior of oscillator strengths as a function of nuclear charge is studied. We believe that our results can guide experimentalists in identifying the fine-structure levels in their future work.
      PubDate: 2016-05-06
      DOI: 10.3390/atoms4020013
      Issue No: Vol. 4, No. 2 (2016)
  • Atoms, Vol. 4, Pages 14: Atom Interferometry in the Presence of an
           External Test Mass

    • Authors: Boris Dubetsky, Stephen Libby, Paul Berman
      First page: 14
      Abstract: The influence of an external test mass on the phase of the signal of an atom interferometer is studied theoretically. Using traditional techniques in atom optics based on the density matrix equations in the Wigner representation, we are able to extract the various contributions to the phase of the signal associated with the classical motion of the atoms, the quantum correction to this motion resulting from atomic recoil that is produced when the atoms interact with Raman field pulses and quantum corrections to the atomic motion that occur in the time between the Raman field pulses. By increasing the effective wave vector associated with the Raman field pulses using modified field parameters, we can increase the sensitivity of the signal to the point where such quantum corrections can be measured. The expressions that are derived can be evaluated numerically to isolate the contribution to the signal from an external test mass. The regions of validity of the exact and approximate expressions are determined.
      PubDate: 2016-04-21
      DOI: 10.3390/atoms4020014
      Issue No: Vol. 4, No. 2 (2016)
  • Atoms, Vol. 4, Pages 15: Novel Ion Trap Design for Strong Ion-Cavity

    • First page: 15
      Abstract: We present a novel ion trap design which facilitates the integration of an optical fiber cavity into the trap structure. The optical fibers are confined inside hollow electrodes in such a way that tight shielding and free movement of the fibers are simultaneously achievable. The latter enables in situ optimization of the overlap between the trapped ions and the cavity field. Through numerical simulations, we systematically analyze the effects of the electrode geometry on the trapping characteristics such as trap depths, secular frequencies and the optical access angle. Additionally, we simulate the effects of the presence of the fibers and confirm the robustness of the trapping potential. Based on these simulations and other technical considerations, we devise a practical trap configuration that isviable to achieve strong coupling of a single ion.
      PubDate: 2016-04-26
      DOI: 10.3390/atoms4020015
      Issue No: Vol. 4, No. 2 (2016)
  • Atoms, Vol. 4, Pages 16: The Faddeev-Merkuriev Differential Equations
           (MFE) and Multichannel 3-Body Scattering Systems

    • Authors: Chi Hu
      First page: 16
      Abstract: Numerical implementation of the modified Faddeev Equation (MFE) is presented in some detail. The Faddeev channel wave function displays unique properties of each and every open channel, respectively. In particular, near resonant energies, the structures of the resonances are beautifully displayed, from which, the life-time of the resonances can be determined by simply using the uncertainty principle. The phase shift matrix, or the K-matrix, provides unique information for each and every resonance. This information enables the identification of the physical formation mechanism of the Gailitis resonances. A few of these resonances, previously known as the mysterious shape resonances, have occurred in a number of different collision systems. The Gailitis resonances are actually produced by a quantized Stark-effect within the various collision systems. Since the Stark-effect is a universal phenomenon, the Gailitis resonances are expected to occur in much broader classes of collision systems. We will present the results of a precision calculation using the MFE method in sufficient detail for interested students who wish to explore the mysteries of nature with a powerful theoretical tool.
      PubDate: 2016-05-03
      DOI: 10.3390/atoms4020016
      Issue No: Vol. 4, No. 2 (2016)
  • Atoms, Vol. 4, Pages 5: Acknowledgement to Reviewers of Atoms in 2015

    • Authors: Atoms Editorial Office
      First page: 5
      Abstract: The editors of Atoms would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2015. [...]
      PubDate: 2016-01-22
      DOI: 10.3390/atoms4010005
      Issue No: Vol. 4, No. 1 (2016)
  • Atoms, Vol. 4, Pages 6: Two Photon Processes in an Atom Confined in
           Gaussian Potential

    • Authors: Sonia Lumb, Shalini Lumb, Vinod Prasad
      First page: 6
      Abstract: Transitions of an atom under the effect of a Gaussian potential and loose spherical confinement are studied. An accurate Bernstein-polynomial (B-polynomial) method has been applied for the calculation of the energy levels and radial matrix elements. The transition probability amplitudes, transparency frequencies, and resonance enhancement frequencies for transitions to various excited states have been evaluated. The effect of the shape of confining potential on these spectral properties is studied.
      PubDate: 2016-02-17
      DOI: 10.3390/atoms4010006
      Issue No: Vol. 4, No. 1 (2016)
  • Atoms, Vol. 4, Pages 7: Guest Editor’s Notes on the
           “Atoms” Special Issue on “Perspectives of Atomic Physics
           with Trapped Highly Charged Ions”

    • First page: 7
      Abstract: The study of highly charged ions (HCI) was pursued first at Uppsala (Sweden), by Edlén and Tyrén in the 1930s. Their work led to the recognition that the solar corona is populated by such ions, an insight which forced massive paradigm changes in solar physics. Plasmas aiming at controlled fusion in the laboratory, laser-produced plasmas, foil-excited swift ion beams, and electron beam ion traps have all pushed the envelope in the production of HCI. However, while there are competitive aspects in the race for higher ion charge states, the real interest lies in the very many physics topics that can be studied in these ions. Out of this rich field, the Special Issue concentrates on atomic physics studies that investigate highly charged ions produced, maintained, and/or manipulated in ion traps. There have been excellent achievements in the field in the past, and including fairly recent work, they have been described by their authors at conferences and in the appropriate journals. The present article attempts an overview over current lines of development, some of which are expanded upon in this Special Issue.
      PubDate: 2016-02-24
      DOI: 10.3390/atoms4010007
      Issue No: Vol. 4, No. 1 (2016)
  • Atoms, Vol. 4, Pages 8: Second Order Stark-Effect Induced Gailitis
           Resonances in e + Ps and p + 7Li

    • Authors: Chi Hu, Zoltan Papp
      First page: 8
      Abstract: We present a detailed comparison between the first order Stark-effect induced Gailitis resonance in e+ + H (n = 2) and the second order Stark-effect induced resonance in e + Ps (n = 1). Common characteristics as well as differences of these resonances will be identified. These results will be used to assess the presence of Gailitis resonances in the scattering of proton on the ground state of 7Li atom. During the lifetime of the Gailitis resonance, nuclear fusion is enhanced by the resonant entry of the proton into the nucleus of 7Li via a compound nuclear energy level of 8Be*.
      PubDate: 2016-02-26
      DOI: 10.3390/atoms4010008
      Issue No: Vol. 4, No. 1 (2016)
  • Atoms, Vol. 4, Pages 9: Merkuriev Cut-off in e+ − H Multichannel
           Scattering Calculations

    • Authors: Vitaly Gradusov, Vladimir Roudnev, Sergey Yakovlev
      First page: 9
      Abstract: We present the results of positron-Hydrogen multichannel scattering calculations performed on the base of Faddeev-Merkuriev equations. We discuss an optimal choice of the Merkuriev’s Coulomb splitting parameters. Splitting the Coulomb potential in two-body configuration space is applicable for a limited energy range. Splitting the potential in three-body configuration space makes it possible to perform calculations in a broader range of energies and to optimize the numerical convergence. Scattering cross sections for zero total angular momentum for all processes between the positronium formation threshold and the third excitation threshold of the Hydrogen atom are reported.
      PubDate: 2016-03-01
      DOI: 10.3390/atoms4010009
      Issue No: Vol. 4, No. 1 (2016)
  • Atoms, Vol. 4, Pages 10: Relativistic Ionization of Hydrogen Atoms by
           Positron Impact

    • Authors: Amal Chahboune, Bouzid Manaut, Elmostafa Hrour, Souad Taj
      First page: 10
      Abstract: Relativistic triple differential cross-sections (TDCS) for ionization of hydrogen atoms by positron impact have been calculated in the symmetric coplanar geometry. We have used Dirac wave functions to describe free electron’s and positron’s sates. The relativistic formalism is examined by taking the non relativistic limit. Present results are compared with those for the corresponding electron-impact case. In the first Born approximation, we found that the TDCS for positron impact ionization exceeds that for electron impact for all energies in accordance with the result obtained by several other theories.
      PubDate: 2016-03-04
      DOI: 10.3390/atoms4010010
      Issue No: Vol. 4, No. 1 (2016)
  • Atoms, Vol. 4, Pages 11: Fundamental Features of Quantum Dynamics Studied
           in Matter-Wave Interferometry—Spin Weak Values and the Quantum

    • Authors: Stephan Sponar, Tobias Denkmayr, Hermann Geppert, Yuji Hasegawa
      First page: 11
      Abstract: The validity of quantum-mechanical predictions has been confirmed with a high degree of accuracy in a wide range of experiments. Although the statistics of the outcomes of a measuring apparatus have been studied intensively, little has been explored and is known regarding the accessibility of quantum dynamics. For these sorts of fundamental studies of quantum mechanics, interferometry using neutron matter-waves in particular, provides almost ideal experimental circumstances. In this device quantum interference between spatially separated beams occurs on a macroscopic scale. Recently, the full determination of weak-values of neutrons 1 2 - spin adds a new aspect to the study of quantum dynamics. Moreover, a new counter-intuitive phenomenon, called quantum Cheshire Cat, is observed in an interference experiment. In this article, we present an overview of these experiments.
      PubDate: 2016-03-11
      DOI: 10.3390/atoms4010011
      Issue No: Vol. 4, No. 1 (2016)
  • Atoms, Vol. 4, Pages 1: Cavity Optomechanics with Ultra Cold Atoms in
           Synthetic Abelian and Non-Abelian Gauge Field

    • Authors: Bikash Padhi, Sankalpa Ghosh
      First page: 1
      Abstract: In this article we present a pedagogical discussion of some of the optomechanical properties of a high finesse cavity loaded with ultracold atoms in laser induced synthetic gauge fields of different types. Essentially, the subject matter of this article is an amalgam of two sub-fields of atomic molecular and optical (AMO) physics namely, the cavity optomechanics with ultracold atoms and ultracold atoms in synthetic gauge field. After providing a brief introduction to either of these fields we shall show how and what properties of these trapped ultracold atoms can be studied by looking at the cavity (optomechanical or transmission) spectrum. In presence of abelian synthetic gauge field we discuss the cold-atom analogue of Shubnikov de Haas oscillation and its detection through cavity spectrum. Then, in the presence of a non-abelian synthetic gauge field (spin-orbit coupling), we see when the electromagnetic field inside the cavity is quantized, it provides a quantum optical lattice for the atoms, leading to the formation of different quantum magnetic phases. We also discuss how these phases can be explored by studying the cavity transmission spectrum.
      PubDate: 2015-12-25
      DOI: 10.3390/atoms4010001
      Issue No: Vol. 4, No. 1 (2015)
  • Atoms, Vol. 4, Pages 2: An Optomechanical Elevator: Transport of a Bloch
           Oscillating Bose–Einstein Condensate up and down an Optical Lattice
           by Cavity Sideband Amplification and Cooling

    • First page: 2
      Abstract: In this paper we give a new description, in terms of optomechanics, of previous work on the problem of an atomic Bose–Einstein condensate interacting with the optical lattice inside a laser-pumped optical cavity and subject to a bias force, such as gravity. An atomic wave packet in a tilted lattice undergoes Bloch oscillations; in a high-finesse optical cavity the backaction of the atoms on the light leads to a time-dependent modulation of the intracavity lattice depth at the Bloch frequency which can in turn transport the atoms up or down the lattice. In the optomechanical picture, the transport dynamics can be interpreted as a manifestation of dynamical backaction-induced sideband damping/amplification of the Bloch oscillator. Depending on the sign of the pump-cavity detuning, atoms are transported either with or against the bias force accompanied by an up- or down-conversion of the frequency of the pump laser light. We also evaluate the prospects for using the optomechanical Bloch oscillator to make continuous measurements of forces by reading out the Bloch frequency. In this context, we establish the significant result that the optical spring effect is absent and the Bloch frequency is not modified by the backaction.
      PubDate: 2015-12-25
      DOI: 10.3390/atoms4010002
      Issue No: Vol. 4, No. 1 (2015)
  • Atoms, Vol. 4, Pages 3: Natural and Unnatural Parity Resonance States in
           the Positron-Hydrogen System with Screened Coulomb Interactions

    • Authors: Ye Ning, Zong-Chao Yan, Yew Ho
      First page: 3
      Abstract: In the present work, we report calculations of resonances in the positron-hydrogen system interacting with screened Coulomb potentials using the method of complex scaling together with employing correlated Hylleraas wave functions. Resonances with natural and unnatural parities are investigated. For the natural parity case, resonance parameters (energy and width) for D-wave resonance states with even parity lying below various positronium and hydrogen thresholds up to the H(N = 4) level are determined. For the unnatural parity case, results for P-even and D-odd resonance states with various screened Coulomb interaction strengths are located below different lower-lying Ps and H thresholds.
      PubDate: 2015-12-26
      DOI: 10.3390/atoms4010003
      Issue No: Vol. 4, No. 1 (2015)
  • Atoms, Vol. 4, Pages 4: Density Functional Theory (DFT) Study on the
           Ternary Interaction System of the Fluorinated Ethylene Carbonate, Li+ and
           Graphene Model

    • Authors: Mami Mutoh, Shigeaki Abe, Teruo Kusaka, Mariko Nakamura, Yasuhiro Yoshida, Junichiro Iida, Hiroto Tachikawa
      First page: 4
      Abstract: The ternary interaction system composed of fluorinated ethylene carbonate, denoted by EC(F), lithium ion (Li+) and a model of nano-structured graphene has been investigated by means of the density functional theory (DFT) method. For comparison, fluorinated vinylene carbonate, denoted by VC(F), was also used. The model of graphene consisting of 14 benzene rings was examined as a nano-structured graphene. The effects of fluorine substitution on the electronic state and binding energy were investigated from a theoretical point of view. It was found that both EC(F) and VC(F) bind to a hexagonal site corresponding to the central benzene ring of the model of the graphene surface. The binding energies of Li+EC(F) and Li+VC(F) to the model of graphene decreased with increasing number of fluorine atoms (n).
      PubDate: 2015-12-29
      DOI: 10.3390/atoms4010004
      Issue No: Vol. 4, No. 1 (2015)
  • Atoms, Vol. 3, Pages 474-494: Electron Impact Excitation and Dielectronic
           Recombination of Highly Charged Tungsten Ions

    • Authors: Zhongwen Wu, Yanbiao Fu, Xiaoyun Ma, Maijuan Li, Luyou Xie, Jun Jiang, Chenzhong Dong
      Pages: 474 - 494
      Abstract: Electron impact excitation (EIE) and dielectronic recombination (DR) of tungsten ions are basic atomic processes in nuclear fusion plasmas of the International Thermonuclear Experimental Reactor (ITER) tokamak. Detailed investigation of such processes is essential for modeling and diagnosing future fusion experiments performed on the ITER. In the present work, we studied total and partial electron-impact excitation (EIE) and DR cross-sections of highly charged tungsten ions by using the multiconfiguration Dirac–Fock method. The degrees of linear polarization of the subsequent X-ray emissions from unequally-populated magnetic sub-levels of these ions were estimated. It is found that the degrees of linear polarization of the same transition lines, but populated respectively by the EIE and DR processes, are very different, which makes diagnosis of the formation mechanism of X-ray emissions possible. In addition, with the help of the flexible atomic code on the basis of the relativistic configuration interaction method, DR rate coefficients of highly charged W37+ to W46+ ions are also studied, because of the importance in the ionization equilibrium of tungsten plasmas under running conditions of the ITER.
      PubDate: 2015-11-20
      DOI: 10.3390/atoms3040474
      Issue No: Vol. 3, No. 4 (2015)
  • Atoms, Vol. 3, Pages 495-508: Two-Photon Collective Atomic Recoil Lasing

    • Authors: James McKelvie, Gordon Robb
      Pages: 495 - 508
      Abstract: We present a theoretical study of the interaction between light and a cold gasof three-level, ladder configuration atoms close to two-photon resonance. In particular, weinvestigate the existence of collective atomic recoil lasing (CARL) instabilities in differentregimes of internal atomic excitation and compare to previous studies of the CARL instabilityinvolving two-level atoms. In the case of two-level atoms, the CARL instability is quenchedat high pump rates with significant atomic excitation by saturation of the (one-photon)coherence, which produces the optical forces responsible for the instability and rapid heatingdue to high spontaneous emission rates. We show that in the two-photon CARL schemestudied here involving three-level atoms, CARL instabilities can survive at high pump rateswhen the atoms have significant excitation, due to the contributions to the optical forces frommultiple coherences and the reduction of spontaneous emission due to transitions betweenthe populated states being dipole forbidden. This two-photon CARL scheme may form thebasis of methods to increase the effective nonlinear optical response of cold atomic gases.
      PubDate: 2015-11-20
      DOI: 10.3390/atoms3040495
      Issue No: Vol. 3, No. 4 (2015)
  • 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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