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  • 1.
    Argenti, Luca
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Ionization branching ratio control with a resonance attosecond clock2010In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 105, p. 053002-Article in journal (Refereed)
    Abstract [en]

    We investigate the possibility to monitor the dynamics of autoionizing states in real-time and control the yields of different ionization channels in helium by simulating extreme ultraviolet (XUV) pump IR-probe experiments focused on the N=2 threshold. The XUV pulse creates a coherent superposition of doubly excited states which is found to decay by ejecting electrons in bursts. Prominent interference fringes in the photoelectron angular distribution of the 2s and 2p ionization channels are observed, along with significant out-of-phase quantum beats in the yields of the corresponding parent ions.

  • 2. Argenti, Luca
    et al.
    Pazourek, Renate
    Feist, Johannes
    Nagele, Stefan
    Liertzer, Matthias
    Persson, Emil
    Burgdoerfer, Joachim
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Photoionization of helium by attosecond pulses: Extraction of spectra from correlated wave functions2013In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 87, no 5, p. 053405-Article in journal (Refereed)
    Abstract [en]

    We investigate the photoionization spectrum of helium by attosecond XUV pulses both in the spectral region of doubly excited resonances as well as above the double ionization threshold. In order to probe for convergence, we compare three techniques to extract photoelectron spectra from the wave packet resulting from the integration of the time-dependent Schrodinger equation in a finite-element discrete variable representation basis. These techniques are projection on products of hydrogenic bound and continuum states, projection onto multichannel scattering states computed in a B-spline close-coupling basis, and a technique based on exterior complex scaling implemented in the same basis used for the time propagation. These methods allow one to monitor the population of continuum states in wave packets created with ultrashort pulses in different regimes. Applications include photo cross sections and anisotropy parameters in the spectral region of doubly excited resonances, time-resolved photoexcitation of autoionizing resonances in an attosecond pump-probe setting, and the energy and angular distribution of correlated wave packets for two-photon double ionization.

  • 3.
    Baggesen, J.C.
    et al.
    Department of Physics and Astronomy, Aarhus University.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Madsen, L.
    Department of Physics and Astronomy, Aarhus University.
    Theory of attosecond absorption spectroscopy in krypton2012In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 85, p. 013415-Article in journal (Refereed)
    Abstract [en]

    A theory for time-domain attosecond pump–attosecond probe photoabsorption spectroscopy is formulated and related to the atomic response. The theory is illustrated through a study of attosecond absorption spectroscopy in krypton. The atomic parameters entering the formulation such as energies and Auger widths, as well as wave functions and dipole coupling matrix elements, are determined by accurate many-body structure calculations. We create a hole in a valence shell by an attosecond pump, couple an inner-shell electron to the hole by an attosecond probe, and then monitor the formation of the hole in this manner. In a second example, a hole is created in an inner shell by the first pulse, and the second probe pulse couples an even more tightly bound state to that hole. The hole decays in this example by Auger electron emission, and the absorption spectroscopy follows the decay of the hole and the associated coherences in real time.

  • 4.
    Bengtsson, Jakob
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Modifying H− resonance asymmetries with short light pulses2012In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 85, no 5, p. 053413-Article in journal (Refereed)
    Abstract [en]

    We present a method, based on time-dependent perturbation theory and complex rotation, to treat the interaction of a short light pulse with a correlated atomic system. The pulse is built from two short and weak pulses with Gaussian envelopes that are centred at two different frequencies.The method is applied to the negative hydrogen ion in the vicinity of a doubly excited resonanceand it is shown that the two light pulses can be used to alter the Fano profile of a resonance.

  • 5.
    Bengtsson, Jakob
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Selstø, Sølve
    Stockholm University, Faculty of Science, Department of Physics.
    Solution of the time-dependent Schrödinger equation using uniform complex scaling2008In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 78, no 3, p. 032502-Article in journal (Refereed)
    Abstract [en]

    The formalism of complex rotation of the radial coordinate is studied in the context of time-dependent systems. The applicability of this method is discussed and illustrated with numerical examples involving atoms exposed to electromagnetic field pulses. Complex rotation proves to be an efficient tool to obtain ionization probabilities and rates. Although, in principle, any information about the system may be obtained from the rotated wave function by transforming it back to its unrotated form, a good description of the ionized part of the wave function is generally subject to numerical challenges. It is, however, found that the combination of complex rotation and Floquet formalism offers an alternative and promising possibility to retrieve the physical information.

  • 6.
    Bengtsson, Jakob
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Selstø, Sølve
    Wave functions associated with time-dependent, complex-scaled Hamiltoniansevaluated on a complex time grid2012In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 85, no 1, p. 013419-Article in journal (Refereed)
    Abstract [en]

    We solve the time-dependent Schr ̈ dinger equation with the method of uniform complex scaling and investigateothe possibility to evaluate the solution on a complex time grid. With this approach it is possible to calculateproperties that relate directly to the continuum part of the complex scaled wave function, such as the photoelectronspectrum after photoabsorption.

  • 7.
    Brandefelt, Nicklas
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    4S resonances of He-below the He+(n=1) threshold1999In: Physical Review A, ISSN 1050-2947, Vol. 59, p. 2691-2696Article in journal (Refereed)
    Abstract [en]

    Resonances of 4Se symmetry in He- are searched for in the region below the He+(n=1) threshold. The energies and widths of the resonances are calculated with an ab initio three-electron description of the ion. The complex rotation method is combined with the use of B splines in a spherical cavity to describe the ion and the decaying channels. Four resonances are found. The first three resonances agree well with experiments. The fourth resonance has not been seen in an experiment yet, due to a small photodetachment cross section and large width

  • 8.
    Brandefelt, Nicklas
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Triply excited 4S resonances of He-2002In: Physical Review A, ISSN 1050-2947, Vol. 65, no 3, p. 032503-032510Article in journal (Refereed)
    Abstract [en]

    Resonances of 4Se symmetry in He- are searched for in the region above the He+(n=1) threshold and below the He+(n=2) threshold. The energies and widths of the resonances are calculated with an ab initio three-electron description of the ion. The complex rotation method is combined with the use of B splines in a spherical cavity to describe the ion and the decay channels. Seven resonances are found and five are presented with energy position and width

  • 9.
    Bürgers, Andre
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Brandefelt, Nicklas
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    The interelectronic angle in doubly excited states and the quality of approximate quantum numbers1998In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, Vol. 31, p. 3181-3198Article in journal (Refereed)
    Abstract [en]

    We present complex scaling calculations of the cosine of the interelectronic angle in doubly excited states of helium below the N = 4 threshold. Since it is directly connected to one of the approximate quantum numbers commonly used to classify doubly excited states, an analysis of this expectation value will give information about the quality of this quantum number. Deviations from the predicted value already occur in the lowest manifold of resonances and are interpreted as a mixture of different basis states. This assertion is tested by a direct doubly excited symmetry basis expansion. Two types of mixing are observed; mixing of basis states to form Rydberg series and mixing of Rydberg series converging to the same threshold. As a possible origin of the basis state mixing which affects the Rydberg series as a whole, avoided crossings in the variation of the resonance energies with respect to the nuclear charge Z are discussed. Mixing between Rydberg series is due to close degeneracies in the resonance energies and connected with avoided crossings in the quantum defect. Both types can easily be distinguished by regarding real and imaginary parts of the complex expectation value

  • 10.
    Carette, Thomas
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Dahlström, J. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Argenti, L.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Multiconfigurational Hartree-Fock close-coupling ansatz: Application to the argon photoionization cross section and delays2013In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 87, no 2, p. 023420-Article in journal (Refereed)
    Abstract [en]

    We present a robust, ab initio method for addressing atom-light interactions and apply it to photoionization of argon. We use a close-coupling ansatz constructed on a multiconfigurational Hartree-Fock description of localized states and B-spline expansions of the electron radial wave functions. In this implementation, the general many-electron problem can be tackled thanks to the use of the ATSP2K libraries [C. Froese Fischer et al., Comput. Phys. Commun. 176, 559 (2007)]. In the present contribution, we combine this method with exterior complex scaling, thereby allowing for the computation of the complex partial amplitudes that encode the whole dynamics of the photoionization process. The method is validated on the 3s3p(6)np series of resonances converging to the 3s extraction. Then, it is used for computing the energy dependent differential atomic delay between 3p and 3s photoemission, and agreement is found with the measurements of Guenot et al. [Phys. Rev. A 85, 053424 (2012)]. The effect of the presence of resonances in the one-photon spectrum on photoionization delay measurements is studied. DOI: 10.1103/PhysRevA.87.023420

  • 11. Chew, Andrew
    et al.
    Douguet, Nicolas
    Cariker, Coleman
    Li, Jie
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Ren, Xiaoming
    Yin, Yanchun
    Argenti, Luca
    Hill, Wendell T.
    Chang, Zenghu
    Attosecond transient absorption spectrum of argon at the L-2,L-3 edge2018In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 97, no 3, article id 031407Article in journal (Refereed)
    Abstract [en]

    Progress in high-harmonic generation has led to high-energy attosecond pulses with cutoff above the carbon 1s edge (283.8 eV). These pulses are essential to extend time-resolved spectroscopies to the water window in order to control electron dynamics in solvated organic species. Here we report a step towards this goal: the measurement, with subcycle time resolution, of the attosecond transient absorption spectrum of argon at the 2p(-1) L-2,L-3 edge (similar to 250 eV) in the presence of a short-wave infrared control pulse. The measurements, supported by theoretical simulations, demonstrate the concurrent role of Auger decay and tunnel ionization in the driven evolution of inner-valence holes of polyelectronic atoms.

  • 12. Cirelli, Claudio
    et al.
    Marante, Carlos
    Heuser, Sebastian
    Petersson, C. L. M.
    Jiménez Galán, Álvaro
    Argenti, Luca
    Zhong, Shiyang
    Busto, David
    Isinger, Marcus
    Nandi, Saikat
    Maclot, Sylvain
    Rading, Linnea
    Johnsson, Per
    Gisselbrecht, Mathieu
    Lucchini, Matteo
    Gallmann, Lukas
    Dahlström, J. Marcus
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    L'Huillier, Anne
    Martin, Fernando
    Keller, Ursula
    Anisotropic photoemission time delays close to a Fano resonance2018In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 955Article in journal (Refereed)
    Abstract [en]

    Electron correlation and multielectron effects are fundamental interactions that govern many physical and chemical processes in atomic, molecular and solid state systems. The process of autoionization, induced by resonant excitation of electrons into discrete states present in the spectral continuum of atomic and molecular targets, is mediated by electron correlation. Here we investigate the attosecond photoemission dynamics in argon in the 20-40 eV spectral range, in the vicinity of the 3s(-1)np autoionizing resonances. We present measurements of the differential photoionization cross section and extract energy and angle-dependent atomic time delays with an attosecond interferometric method. With the support of a theoretical model, we are able to attribute a large part of the measured time delay anisotropy to the presence of autoionizing resonances, which not only distort the phase of the emitted photoelectron wave packet but also introduce an angular dependence.

  • 13.
    Dahlström, J. M.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Carette, Thomas
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Diagrammatic approach to attosecond delays in photoionization2012In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 86, no 6, p. 061402-Article in journal (Refereed)
    Abstract [en]

    We study laser-assisted photoionization by attosecond pulses using a time-independent formalism based on diagrammatic many-body perturbation theory. Our aim is to provide an ab initio route to the delays for this above-threshold ionization process, which is essential for a quantitative understanding of attosecond metrology. We present correction curves for characterization schemes of attosecond pulses, such as streaking, that account for the delayed atomic response in ionization from neon and argon. We also verify that photoelectron delays from many-electron atoms can be measured using similar schemes if, instead, the so-called continuum-continuum delay is subtracted. Our method is general and it can be extended also to more complex systems and additional correlation effects can be introduced systematically. DOI: 10.1103/PhysRevA.86.061402

  • 14.
    Dahlström, J. Marcus
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Max Planck Society, Germany; Centre for Free Electron Laser Science, Germany.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Study of attosecond delays using perturbation diagrams and exterior complex scaling2014In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 47, no 12, p. 124012-Article in journal (Refereed)
    Abstract [en]

    We describe in detail how attosecond delays in laser-assisted photoionization can be computed using perturbation theory based on two-photon matrix elements. Special emphasis is laid on above-threshold ionization, where the electron interacts with an infrared field after photoionization by an extreme ultraviolet field. Correlation effects are introduced using diagrammatic many-body theory to the level of the random-phase approximation with exchange. Our aim is to provide an ab initio route to correlated multi-photon processes that are required for an accurate description of experiments on the attosecond time scale. Here, our results are focused on photoionization of the M-shell of argon atoms, where experiments have been carried out using the so-called reconstruction of attosecond beating by the two-photon interference transitions technique. An influence of autoionizing resonances in attosecond delay measurements is observed. Further, it is shown that the delay depends on both detection angle of the photoelectron and energy of the probe photon.

  • 15.
    Dahlström, Jan Marcus
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Lund University, Sweden.
    Pabst, Stefan
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Attosecond transient absorption of a bound wave packet coupled to a smooth continuum2017In: Journal of Optics, ISSN 2040-8978, E-ISSN 2040-8986, Vol. 19, no 11, article id 114004Article in journal (Refereed)
    Abstract [en]

    We investigate the possibility of using transient absorption of a coherent bound electron wave packet in hydrogen as an attosecond pulse characterization technique. In a recent work, we have shown that photoionization of such a coherent bound electron wave packet opens up for pulse characterization with unprecedented temporal accuracy-independent of the atomic structure-with maximal photoemission at all kinetic energies given a wave packet with zero relative phase (Pabst and Dahlstrom Phys. Rev. A 94 13411 (2016)). Here, we perform numerical propagation of the time-dependent Schrodinger equation and analytical calculations based on perturbation theory to show that the energy-resolved maximal absorption of photons from the attosecond pulse does not uniquely occur at a zero relative phase of the initial wave packet. Instead, maximal absorption occurs at different relative wave packet phases, distributed as a non-monotonous function with a smooth -pi/2 shift across the central photon energy (given a Fourier-limited Gaussian pulse). Similar results are also found in helium. Our finding is surprising, because it implies that the energy-resolved photoelectrons are not mapped one-to-one with the energy-resolved absorbed photons of the attosecond pulse.

  • 16. Dahlström, Jan Marcus
    et al.
    Pabst, Stefan
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Pulse analysis by delayed absorption from a coherently excited atom2019In: Apl Photonics, ISSN 2378-0967, Vol. 4, no 1, article id 011101Article in journal (Refereed)
    Abstract [en]

    In this tutorial, we provide a short review of attosecond pulse characterization techniques and a pedagogical account of a recently proposed method called Pulse Analysis by Delayed Absorption (PANDA) [S. Pabst and J. M. Dahlstrom, Phys. Rev. A 94, 013411 (2016)]. We discuss possible implementations of PANDA in alkali atoms using either principal quantum number wave packets or spin-orbit wave packets. The main merit of the PANDA method is that it can be used as a pulse characterization method that is free from atomic latency effects, such as scattering phase shifts and long-lived atomic resonances. Finally, we propose that combining the PANDA method with angle-resolved photoelectron detection should allow for experimental measurements of attosecond delays in photoionization from bound wave packets on the order of tens of attoseconds.

  • 17. Della Picca, R.
    et al.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Multicolor XUV above threshold ionization of argon2015In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 48, no 24, article id 245202Article in journal (Refereed)
    Abstract [en]

    Argon photo-electron spectra produced by short-pulse extreme ultraviolet radiation, and with particular emphasis on the two-photon absorption region, is analyzed theoretically. The electromagnetic pulse is modeled to resemble experimentally available pulses and is built from a range of high-harmonics from an 800 nm laser. The photo-electron spectra show a characteristic peak structure due to the absorption of different combinations of photons, where the relative peak intensity is very sensitive to both the XUV pulse parameters and the target description. The theoretical result is further compared with experimental data, and good qualitative agreement is found.

  • 18. Fröstad, T.
    et al.
    Hansen, J. P.
    Wesslén, Carl Johan
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Räsänen, E.
    Two-electron quantum dot in tilted magnetic fields: Sensitivity to the confinement model2013In: European Physical Journal B: Condensed Matter Physics, ISSN 1434-6028, E-ISSN 1434-6036, Vol. 86, no 10, article id 430Article in journal (Refereed)
    Abstract [en]

    Semiconductor quantum dots are conventionally treated within the effective-mass approximation and a harmonic model potential in the two-dimensional plane for the electron confinement. The validity of this approach depends on the type of the quantum-dot device as well as on the number of electrons confined in the system. Accurate modeling is particularly demanding in the few-particle regime, where screening effects are diminished and thus the system boundaries may have a considerable effect on the confining potential. Here we solve the numerically exact two-electron states in both harmonic and hard-wall model quantum dots subjected to tilted magnetic fields. Our numerical results enable direct comparison against experimental singlet-triplet energy splittings. Our analysis shows that hard and soft wall models produce qualitatively different results for quantum dots exposed to tilted magnetic fields. Hence, we are able to address the sensitivity of the two-body phenomena to the modeling, which is of high importance in realistic spin-qubit design.

  • 19.
    Genkin, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Ferro, Fabrizio
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Environmentally induced shift of the quantum arrival time2009In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. A80, p. 052112-Article in journal (Refereed)
    Abstract [en]

    Usinga simple model potential, we study the effects of weakMarkovian dissipation on the quantum arrival time. The interaction withthe environment is incorporated into the dynamics through a Markovianmaster equation of Lindblad type, which allows us to comparetime-of-arrival distributions and approximate crossing probabilities for different dissipation strengthsand temperatures. We also establish a connection to an earlierstudy where quantum tunneling with dissipation was investigated, which leadsus to some conclusions concerning the formulation of the continuityequation in the Lindblad theory.

  • 20.
    Genkin, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Description of resonance decay by Lindblad operators2008In: Journal of Physics A: Mathematical and Theoretical, ISSN 1751-8113, Vol. 41, no 42, p. 425303-Article in journal (Refereed)
    Abstract [en]

    Using an analytical model potential which contains resonant and bound states, we show that the decay of the resonances can be simulated by Lindblad operators. For that purpose, the unitary time evolution of an initial Gaussian wave packet in the model potential is compared with the non-unitary time evolution, obtained by solving the Lindblad equation, of the same wave packet in a potential which coincides with the model potential in the region of interest but does not contain resonances. In the latter case, dissipative effects are accounted for by Lindblad operators which lead to phenomenological friction and diffusion constants in the equations of motion. We suggest how those constants can be determined in a non-heuristic way, being directly connected to the width of the resonance in the model potential which we calculate using the complex rotation method.

  • 21.
    Genkin, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Effects of screened Coulomb impurities on autoionizing two-electron resonances in spherical quantum dots2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 12, p. 125315-Article in journal (Refereed)
    Abstract [en]

    In a recent paper [Phys. Rev. B 78, 075316 (2008)], Sajeev and Moiseyev demonstrated that the bound-to-resonant transitions and lifetimes of autoionizing states in spherical quantum dots can be controlled by varying the confinement strength. In the present paper, we report that such control can in some cases be compromised by the presence of Coulomb impurities. It is demonstrated that a screened Coulomb impurity placed in the vicinity of the dot center can lead to bound-to-resonant transitions and to avoided-crossinglike-behavior when the screening of the impurity charge is varied. It is argued that these properties also can have impact on electron transport through quantum dot arrays.

  • 22.
    Genkin, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Environmental effects on the phase space dynamics and decoherence time scale of a charged particle in a Penning trap2009In: Journal of Physics A: Mathematical and Theoretical, ISSN 1751-8113, Vol. 42, no 38, p. 385302-Article in journal (Refereed)
    Abstract [en]

    We study the time evolution of a charged particle in a Penning trap in the framework of open quantum systems. The interaction with the environment istaken into account by imposing Lindblad operators which are linear in the canonical variables. For the special case of a proton in an asymmetricPenning trap we compare the dynamics with earlier results obtained from the unitary time-dependent Schrödinger equation. A possibility to estimatethe spatial decoherence time of the system is discussed, and approximate decoherence time scales are given for different ions.

  • 23.
    Genkin, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    On the Penning trap coherent states2009In: Journal of Physics A: Mathematical and Theoretical, ISSN 1751-8113, Vol. 42, no 27, p. 275305-Article in journal (Refereed)
    Abstract [en]

    Recently, a class of coherent states of a particle in a Penning trap was derived byFernandez and Velazquez (J. Phys. A: Math. Theor. 42 (2009) 085304).By means of the Wigner function and density matrix associated with these states,we show that they are fully consistent with Morikawa's definition of the decoherence degree and hence they provide apossibility to directly access the decoherence process in a Penning trap.

  • 24.
    Genkin, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Possibility of resonant capture of antiprotons by highly charged hydrogenlike ions2009In: European Physical Journal D: Atomic, Molecular and Optical Physics, ISSN 1434-6060, E-ISSN 1434-6079, Vol. 51, no 2, p. 205-212Article in journal (Refereed)
    Abstract [en]

    Recently, an experimetal setup was proposed by Lapierre et al (in Physics with ultra slow antiproton beams, AIP Conference Proceedings, edited by Y. Yamazaki and M. Wada (2005), vol. 793, p. 361) which would allow antiprotons and highly charged ions to collide repeatedly in an electron beam ion trap (EBIT) due to a nested trap configuration. As mentioned by the authors, such a setup may open the possibility to study antiproton capture into well-defined states through a resonant process which involves simultaneous electron excitation. In the present work, we give some theoretical estimations of the feasibility of that process.

  • 25.
    Genkin, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Waltersson, Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Estimation of the spatial decoherence time in circular quantum dots2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. B79, no 24, p. 245310-Article in journal (Refereed)
    Abstract [en]

    We propose a simple phenomenological model to estimate the spatial decoherence time in quantum dots. The dissipative phase space dynamicsis described in terms of the density matrix and the corresponding Wigner function, which are derived from a master equation with Lindblad operatorslinear in the canonical variables. The formalism was initially developed to describe diffusion and dissipation in deep inelastic heavy ioncollisions, but also an application to quantum dots is possible.It allows us to study the dependence of the decoherence rate on the dissipation strength, the temperature and an external magnetic field, which isdemonstrated in illustrative calculations on a circular GaAs one-electron quantum dot.

  • 26. Guenot, D.
    et al.
    Klunder, K.
    Arnold, C. L.
    Kroon, D.
    Dahlström, J. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Miranda, M.
    Fordell, T.
    Gisselbrecht, M.
    Johnsson, P.
    Mauritsson, J.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Maquet, A.
    Taieb, R.
    L'Huillier, A.
    Kheifets, A. S.
    Photoemission time delay measurements and calculations close to the 3s ionization cross section minimum in ar2012In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 85, no 5, p. 053424-Article in journal (Refereed)
    Abstract [en]

    We present experimental measurements and theoretical calculations of photoionization time delays from the 3s and 3p shells in Ar in the photon energy range of 32-42 eV. The experimental measurements are performed by interferometry using attosecond pulse trains and the infrared laser used for their generation. The theoretical approach includes intershell correlation effects between the 3s and 3p shells within the framework of the random-phase approximation with exchange. The connection between single-photon ionization and the two-color two-photon ionization process used in the measurement is established using the recently developed asymptotic approximation for the complex transition amplitudes of laser-assisted photoionization. We compare and discuss the theoretical and experimental results, especially in the region where strong intershell correlations in the 3s -> kp channel lead to an induced Cooper minimum in the 3s ionization cross section.

  • 27.
    Haeffler, Gunnar
    et al.
    Department of Physics, Chalmers University of Technology and Göteborg University.
    Kiyan, Igor Yu.
    Department of Physics, Chalmers University of Technology and Göteborg University.
    Berzinsh, Uldis
    Department of Physics, Chalmers University of Technology and Göteborg University.
    Hanstorp, Dag
    Department of Physics, Chalmers University of Technology and Göteborg University.
    Brandefelt, Nicklas
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Pegg, David J.
    Department of Physics, University of Tennessee, Knoxville.
    Strongly correlated states in the Li- ion2001In: Physical Review A, ISSN 1050-2947, Vol. 63, no 5, p. 053409-053412Article in journal (Refereed)
    Abstract [en]

    A collinear laser-ion beam apparatus has been used to investigate resonance structure in the Li(3s)+e-(kp) partial photodetachment cross section below the Li(6p) threshold. A complex rotation calculation was used to identify the strongly correlated, doubly excited states of the quasi-two-electron ion Li- that are responsible for the observed resonances. These represent the most highly excited states of Li- observed thus far. Several members of a strong “+” type series were observed as well as at least one resonance with “-” type character. In particular, we report on an observation of a resonance that violates the Δν=0 propensity rule.

  • 28. Heuser, Sebastian
    et al.
    Galan, Álvaro Jiménez
    Cirelli, Claudio
    Marante, Carlos
    Sabbar, Mazyar
    Boge, Robert
    Lucchini, Matteo
    Gallmann, Lukas
    Ivanov, Igor
    Kheifets, Anatoli S.
    Dahlström, J. Marcus
    Stockholm University, Faculty of Science, Department of Physics. Max Planck Institute for the Physics of Complex Systems, Germany; Center for Free-Electron Laser Science, Germany.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Argenti, Luca
    Martin, Fernando
    Keller, Ursula
    Angular dependence of photoemission time delay in helium2016In: Physical Review A, ISSN 2469-9926, Vol. 94, no 6, article id 063409Article in journal (Refereed)
    Abstract [en]

    Time delays of electrons emitted from an isotropic initial state with the absorption of a single photon and leaving behind an isotropic ion are angle independent. Using an interferometric method involving XUV attosecond pulse trains and an IR-probe field in combination with a detection scheme, which allows for full three-dimensional momentum resolution, we show that measured time delays between electrons liberated from the 1s(2) spherically symmetric ground state of helium depend on the emission direction of the electrons relative to the common linear polarization axis of the ionizing XUV light and the IR-probing field. Such time delay anisotropy, for which we measure values as large as 60 as, is caused by the interplay between final quantum states with different symmetry and arises naturally whenever the photoionization process involves the exchange of more than one photon. With the support of accurate theoretical models, the angular dependence of the time delay is attributed to small phase differences that are induced in the laser-driven continuum transitions to the final states. Since most measurement techniques tracing attosecond electron dynamics involve the exchange of at least two photons, this is a general and significant effect that must be taken into account in all measurements of time delays involving photoionization processes.

  • 29. Isinger, M.
    et al.
    Squibb, R. J.
    Busto, D.
    Zhong, S.
    Harth, A.
    Kroon, D.
    Nandi, S.
    Arnold, C. L.
    Miranda, M.
    Dahlström, J. Marcus
    Stockholm University, Faculty of Science, Department of Physics. Lund University, Sweden.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Feifel, R.
    Gisselbrecht, M.
    L'Huillier, A.
    Photoionization in the time and frequency domain2017In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 358, no 6365, p. 893-896Article in journal (Refereed)
    Abstract [en]

    Ultrafast processes in matter, such as the electron emission after light absorption, can now be studied using ultrashort light pulses of attosecond duration (10-18 seconds) in the extreme ultraviolet spectral range. The lack of spectral resolution due to the use of short light pulses has raised issues in the interpretation of the experimental results and the comparison with theoretical calculations. We determine photoionization time delays in neon atoms over a 40-electron volt energy range with an interferometric technique combining high temporal and spectral resolution. We spectrally disentangle direct ionization from ionization with shake-up, in which a second electron is left in an excited state, and obtain excellent agreement with theoretical calculations, thereby solving a puzzle raised by 7-year-old measurements.

  • 30.
    Kjellsson Lindblom, Tor
    et al.
    Stockholm University, Faculty of Science, Department of Physics. The University of Electro-Communications, Japan.
    Førre, Morten
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Selstø, Sølve
    Semirelativistic Schrodinger Equation for Relativistic Laser-Matter Interactions2018In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 121, no 25, article id 253202Article in journal (Refereed)
    Abstract [en]

    A semirelativistic formulation of light-matter interaction is derived using the so called propagation gauge and the relativistic mass shift. We show that relativistic effects induced by a superintense laser field can, to a surprisingly large extent, be accounted for by the Schrodinger equation, provided that we replace the rest mass in the propagation gauge Hamiltonian by the corresponding time-dependent field-dressed mass. The validity of the semirelativistic approach is tested numerically on a hydrogen atom exposed to an intense extreme ultraviolet laser pulse strong enough to accelerate the electron towards relativistic velocities. It is found that while the results obtained from the ordinary (nonrelativistic) Schrodinger equation generally differ from those of the Dirac equation, demonstrating that relativistic effects are significant, the semirelativistic formulation provides results in quantitative agreement with a fully relativistic treatment.

  • 31.
    Kjellsson, Tor
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Førre, Morten
    Skjerlie Simonsen, Aleksander
    Selstø, Sølve
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Alternative gauge for the description of the light-matter interaction in a relativistic framework2017In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 96, no 2, article id 023426Article in journal (Refereed)
    Abstract [en]

    We present a generalized velocity gauge form of the relativistic laser-matter interaction. In comparison with the (equivalent) regular minimal coupling description, this form of light-matter interaction results in superior convergence properties for the numerical solution of the time-dependent Dirac equation. This applies both to the numerical treatment and, more importantly, to the multipole expansion of the laser field. The advantages of the alternative gauge is demonstrated in hydrogen by studies of the dynamics following the impact of superintense laser pulses of extreme ultraviolet wavelengths and subfemtosecond duration.

  • 32.
    Kjellsson, Tor
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Selstø, Sølve
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Relativistic ionization dynamics for a hydrogen atom exposed to superintense XUV laser pulses2017In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 95, no 4, article id 043403Article in journal (Refereed)
    Abstract [en]

    We present a theoretical study of the ionization dynamics of a hydrogen atom exposed to attosecond laser pulses in the extreme ultraviolet region at very high intensities. The pulses are such that the electron is expected to reach relativistic velocities, thus necessitating a fully relativistic treatment. We solve the time-dependent Dirac equation and compare its predictions with those of the corresponding nonrelativistic Schrodinger equation. We find that as the electron is expected to reach about 20% of the speed of light, relativistic corrections introduce a finite yet small decrease in the probability of ionizing the atom.

  • 33. Kotur, M.
    et al.
    Guenot, D.
    Jimenez-Galan, A.
    Kroon, D.
    Larsen, E. W.
    Louisy, M.
    Bengtsson, S.
    Miranda, M.
    Mauritsson, J.
    Arnold, C. L.
    Canton, S. E.
    Gisselbrecht, M.
    Carette, Thomas
    Stockholm University, Faculty of Science, Department of Physics.
    Dahlström, J. Marcus
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Maquet, A.
    Argenti, L.
    Martin, F.
    L'Huillier, A.
    Spectral phase measurement of a Fano resonance using tunable attosecond pulses2016In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 7, article id 10566Article in journal (Refereed)
    Abstract [en]

    Electron dynamics induced by resonant absorption of light is of fundamental importance in nature and has been the subject of countless studies in many scientific areas. Above the ionization threshold of atomic or molecular systems, the presence of discrete states leads to autoionization, which is an interference between two quantum paths: direct ionization and excitation of the discrete state coupled to the continuum. Traditionally studied with synchrotron radiation, the probability for autoionization exhibits a universal Fano intensity profile as a function of excitation energy. However, without additional phase information, the full temporal dynamics cannot be recovered. Here we use tunable attosecond pulses combined with weak infrared radiation in an interferometric setup to measure not only the intensity but also the phase variation of the photoionization amplitude across an autoionization resonance in argon. The phase variation can be used as a fingerprint of the interactions between the discrete state and the ionization continua, indicating a new route towards monitoring electron correlations in time.

  • 34.
    Lindroth, E
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Bürgers, A
    Stockholm University, Faculty of Science, Department of Physics.
    Brandefelt, N
    Stockholm University, Faculty of Science, Department of Physics.
    Relativistic effects on the H- resonances converging to the H(n=2) threshold threshold1998In: Physical Review A, ISSN 1050-2947, Vol. 57, no 2, p. R685-R688Article in journal (Refereed)
    Abstract [en]

    The series of H- resonances of 1Po symmetry predicted to converge exponentially to all thresholds has been investigated below the H(n=2) threshold. It is shown that the series will be terminated already after the third resonance when the relativistic and radiative splitting of the H(n=2) states is considered. Resonance parameters of this third resonance have been calculated with highly correlated wave functions. The resonance is predicted to be situated 19μeV below H(2p1/2) with a width of 0.06μeV. Accurate resonance parameters are also given for the first two resonances and the photoabsorption cross section is calculated for the threshold region.

  • 35.
    Lindroth, Eva
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Argenti, Luca
    Atomic Resonance States and Their Role in Charge-Changing Processes2012In: Advances in Quantum Chemistry, vol 63 / [ed] Cleanthes A. Nicolaides, Erkki Brändas and John R. Sabin, Elsevier, 2012, p. 247-308Chapter in book (Refereed)
    Abstract [en]

    Resonant states play a governing role in many charge-changing processes in atoms; the photoionization of atoms in gas phase and the corresponding time-reversed process of dielectronic recombinations being the two most prominent and well-known examples. This is so thanks to their strongly localized character, which leads to large transition matrix elements and to the unusually long timescale at which their dynamics unfolds, if compared to free-electron wave packets. Many resonances correspond also to highly correlated electronic states. Hence, on the one hand, high-resolution extreme ultraviolet (XUV) and soft x-ray photoelectron spectroscopy, which give access to electronic resonances, provide unique insight into the effects of electronic correlation in the energy domain; on the other hand, new laser techniques able to produce light pulses of sub-femtosecond duration give a complementary, much needed, view of electronic correlation resolved in time. Here, we discuss resonances in atoms and atomic ions in all these respects. First, we survey how resonances can be accurately localized and characterized with complex scaling, standard scattering techniques and, for heavy ions, with relativistic many-body theory. The need for high precision is particularly stringent in the latter case since resonances located just above the ionization threshold, and thus whose parameters are most affected by numerical uncertainties, are often the most important for recombination. Second, we examine how the spectral properties of resonances translate in the time domain and how the course of the ionization process can be steered with external ultra-short driving laser pulses.

  • 36.
    Lindroth, Eva
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Argenti, Luca
    Stockholm University, Faculty of Science, Department of Physics.
    Bengtsson, Jakob
    Stockholm University, Faculty of Science, Department of Physics.
    Ferro, Fabrizio
    Stockholm University, Faculty of Science, Department of Physics.
    Genkin, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Selstø, Sølve
    Stockholm University, Faculty of Science, Department of Physics.
    The Structure Behind it All2009In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 194, p. 012001-Article in journal (Refereed)
    Abstract [en]

    The talk discussed collisions where the structure of the systems involved plays a decisive role for the outcome of the event. For many types of charge changing processes the presence of resonant states can change the probability for a certain reaction by orders of magnitude. One example of this is electron-ion recombination where the resonant states are doubly or even multiply excited states lying above the ionization threshold of the recombined ion. The concept of a resonant state is discussed with the help of a simple model. The influence of such states is then illustrated through a few examples where some different calculational methods are compared with experiments. Finally, the possibility to also obtain accurate spectroscopical information from a collisional process is discussed

  • 37.
    Lindroth, Eva
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Dahlström, Jan Marcus
    Stockholm University, Faculty of Science, Department of Physics.
    Attosecond delays in laser-assisted photodetachment from closed-shell negative ions2017In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 96, no 1, article id 013420Article in journal (Refereed)
    Abstract [en]

    We study laser-assisted photodetachment time delays by attosecond pulse trains from the closed-shell negative ions F- and Cl. We investigate the separability of the delay into two contributions: (i) the Wigner-like delay associated with one-photon ionization by the attosecond pulse train and (ii) the delay associated with the exchange of an additional laser photon in the presence of the potential of the remaining target. Based on the asymptotic form of the wave packet, the latter term is expected to be negligible because the ion is neutralized, leading to a vanishing laser-ion interaction with increasing electron-atom separation. While this asymptotic behavior is verified at high photoelectron energies, we also quantify sharp deviations at low photoelectron energies. Further, these low-energy delays are clearly different for the two studied anions, indicating a breakdown of the universality of laser-ion-induced delays. The fact that the short-range potential can induce a delay of as much as 50 as can have implications for the interpretation of delay measurements also in other systems that lack long-range potential.

  • 38.
    Mahmood, Sultan
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Ali, Safdar
    Stockholm University, Faculty of Science, Department of Physics.
    Orban, Istvan
    Stockholm University, Faculty of Science, Department of Physics.
    Tashenov, Stanislav
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Schuch, Reinhold
    Stockholm University, Faculty of Science, Department of Physics.
    Recombination and electron impact excitation rate coefficients for S XV AND S XVI2012In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 754, no 2, p. 86-Article in journal (Refereed)
    Abstract [en]

    Recombination and electron impact excitation of S14+ and S15+ ions was measured at the Stockholm refrigerated electron beam ion trap. The collision energy range was 1.4-3 keV, where we covered the KLL, KLM, KLN, and KLO dielectronic recombination resonances resulting in S13+ and S14+ ions. The recombination rates were obtained by detecting the charge state distribution with a newly developed time-of-flight technique. Resonance energies and cross sections calculated within the relativistic many-body perturbation theory for S15+ agree well with the experimental data. The temperature dependent rate coefficients have been extracted from the measured rates and compared with calculations from literature used for studies of collisionally ionized astrophysical plasmas. A good agreement for S15+ was obtained, while the plasma rates for S14+ were 23% lower than the so far published values. In addition to the time-of-flight spectra, the x-ray spectra, produced mainly by photo-recombination and excitation, have been also collected. The combination of these two measurements allowed us to separate the photo-recombination and the excitation spectra, and the excitation rate coefficients for summed intensities with known fractions of S14+ and S15+ ions were extracted.

  • 39. Marante, Carlos
    et al.
    Klinker, Markus
    Kjellsson, Tor
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    González-Vázquez, Jesus
    Argenti, Luca
    Martín, Fernando
    Photoionization using the XCHEM approach: Total and partial cross sections of Ne and resonance parameters above the 2s(2)2p(5) threshold2017In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 96, no 2, article id 022507Article in journal (Refereed)
    Abstract [en]

    The XCHEM approach interfaces well established quantum chemistry packages with scattering numerical methods in order to describe single-ionization processes in atoms and molecules. This should allow one to describe electron correlation in the continuum at the same level of accuracy as quantum chemistry methods do for bound states. Here we have applied this method to study multichannel photoionization of Ne in the vicinity of the autoionizing states lying between the 2s(2)2p(5) and 2s(2)p(6) ionization thresholds. The calculated total photoionization cross sections are in very good agreement with the absolute measurement of Samson et al. [J. Electron Spectrosc. Relat. Phenom. 123, 265 (2002)], and with independent benchmark calculations performed at the same level of theory. From these cross sections, we have extracted resonance positions, total autoionization widths, Fano profile parameters, and correlation parameters for the lowest three autoionizing states. The values of these parameters are in good agreement with those reported in earlier theoretical and experimental work. We have also evaluated beta asymmetry parameter and partial photoionization cross sections and, from the latter, partial autoionization widths and Starace parameters for the same resonances, not yet available in the literature. Resonant features in the calculated beta parameter are in good agreement with the experimental observations. We have found that the three lowest resonances preferentially decay into the 2p(-1) epsilon d continuum rather than into the 2p(-1) epsilon s one [Phys. Rev. A 89, 043415 (2014)], in agreement with previous expectations, and that in the vicinity of the resonances the partial 2p(-1) epsilon s cross section can be larger than the 2p(-1) epsilon d one, in contrast with the accepted idea that the latter should amply dominate in the whole energy range. These results show the potential of the XCHEM approach to describe highly correlated process in the ionization continuum of many-electron systems, in particular molecules, for which the XCHEM code has been specifically designed.

  • 40. Månsson, Erik P.
    et al.
    Guenot, Diego
    Arnold, Cord L.
    Kroon, David
    Kasper, Susan
    Dahlström, Marcus
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Kheifets, Anatoli S.
    L'Huillier, Anne
    Sörensen, Stacey L.
    Gisselbrecht, Mathieu
    Double ionization probed on the attosecond timescale2014In: Nature Physics, ISSN 1745-2473, E-ISSN 1745-2481, Vol. 10, no 3, p. 207-211Article in journal (Refereed)
    Abstract [en]

    Double ionization following the absorption of a single photon is one of the most fundamental processes requiring interaction between electrons(1-3). Information about this interaction is usually obtained by detecting emitted particles without access to real-time dynamics. Here, attosecond light pulses(4,5), electron wave packet interferometry(6) and coincidence techniques(7) are combined to measure electron emission times in double ionization of xenon using single ionization as a clock, providing unique insight into the two-electron ejection mechanism. Access to many-particle dynamics in real time is of fundamental importance for understanding processes induced by electron correlation in atomic, molecular and more complex systems.

  • 41. Müller, A.
    et al.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Bari, S.
    Borovik, A.
    Hillenbrand, P-M
    Holste, K.
    Indelicato, P.
    Kilcoyne, A. L. D.
    Klumpp, S.
    Martins, M.
    Viefhaus, J.
    Wilhelm, P.
    Schippers, S.
    Photoionization of metastable heliumlike C4+ (1s2s S-3(1)) ions: Precision study of intermediate doubly excited states2018In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 98, no 3, article id 033416Article in journal (Refereed)
    Abstract [en]

    In a joint experimental and theoretical endeavor, photoionization of metastable C4+ (1s2s S-3(1)) ions via intermediate levels with hollow, double-K-vacancy configurations 2s2p, 2s3p, 2p3s, 2p3d, 2s4p, 2p4s, and 2p4d has been investigated. High-resolution photon-ion merged-beams measurements were carried out with the resolving power reaching up to 25 800 which is sufficient to separate the leading fine-structure components of the 2s2p P-3 term. Many-body perturbation theory was employed to determine level-to-level cross sections for K-shell excitation with subsequent autoionization. The resonance energies were calculated with inclusion of electron correlation and radiative contributions. Their uncertainties are estimated to be below +/- 1 meV. Detailed balance confirms the present photoionization cross-section results by comparison with previous dielectronic-recombination measurements. The high accuracy of the theoretical transition energies together with the present experimental results qualify photoabsorption resonances in heliumlike ions as new, greatly improved energy-reference standards at synchrotron radiation facilities.

  • 42.
    Nikolić, Dragan
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Kieslich, Stefan
    Brandau, Carsten
    Schippers, Stefan
    Shi, Wei
    Müller, Alfred
    Gwinner, Gerald
    Schnell, Michael
    Wolf, Andreas
    Dielectronic recombination resonances in Na8+2004In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 70, no 6Article in journal (Refereed)
    Abstract [en]

    The electron-ion recombination spectrum of the Li-like Na8+ ion in the energy range 0.0–0.5 eV is presented. Experimental results obtained by storage-ring techniques are compared with a calculated spectrum, based on a combination of relativistic many-body methods and complex rotation, and the agreement is found to be very good. The deviations between measured and calculated dielectronic recombination resonance energies are usually below about 2 meV with a maximum difference at 5.5 meV, while the theoretical cross sections deviate by at most 20% from the experiment. The recombination spectrum in the investigated energy region is determined by the 2pj7ℓj Rydberg manifold of dielectronic recombination resonances, comprising 61 states within half an eV above the ground state of Na8+. The theoretical resonance parameters of all contributing states are provided.

  • 43.
    Orban, Istvan
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Glans, P.
    Altun, Z.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Källberg, Anders
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Schuch, Reinhold
    Stockholm University, Faculty of Science, Department of Physics.
    Determination of the recombination rate coefficients for Na-like Si IV forming Mg-like Si III2006In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 459, no 1, p. 291-296Article in journal (Refereed)
    Abstract [en]

    Aims. Absolute, total recombination rate coefficients for Si iv were determined using the CRYRING heavy-ion storage ring.Calculated rate coefficients were used to estimate recombination into states that could not be detected in the experiment becauseof field ionization. Total, as well as separate, radiative and dielectronic plasma recombination rate coefficients were determined.Methods. Stored ions were merged with an expanded electron beam in the electron cooler section of the storage ring. Recombined ionswere separated from the stored ion beam in the first dipole magnet after the electron cooler and were detected with unity efficiency.The absolute radiative and dielectronic recombination rate coefficients were obtained over a center-of-mass energy range of 0−20 eV,covering Δn = 0 core excitations up to the 3s → 3d series limit. The results of an intermediate coupling autostructure calculationwere compared with the experiment. The theoretical results were also used to estimate the contribution to dielectronic recombinationby high Rydberg states, which were not detected because of field ionization. The spectra were convoluted with Maxwell-Boltzmannenergy distributions in the 103−106 K temperature range.Results. The resulting plasma recombination rate coefficients are presented and compared with theoretical results frequently usedfor plasma modeling. In the 103−104 K range, a significant underestimation of the calculated dielectronic recombination plasma ratecoefficients was observed. Above 3 × 104 K, the agreement between our dielectronic recombination plasma rate coefficients and twoof the previously published rate coefficients is better than 20%.Conclusions. The observed differences between the experimental and calculated recombination rate coefficients at low temperaturesreflect the need for benchmarking experiments. Our experimentally-derived rate coefficients can guide the development of bettertheoretical models and lead to more accurately-calculated rate coefficients.

  • 44.
    Orban, Istvan
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Glans, Peter
    Department of Engineering, Physics and Mathematics, Mid Sweden University.
    Schuch, Reinhold
    Stockholm University, Faculty of Science, Department of Physics.
    Spectroscopic study of doubly excited states in Mg-likeSi using dielectronic recombination2007In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 40, no 5, p. 1063-1080Article in journal (Refereed)
    Abstract [en]

    We present calculated and experimentally derived electron–ion recombinationrate coefficients for Na-like Si IV, recombining into Mg-like Si III, andprovide accurate spectroscopic data for doubly excited states located above theionization threshold of Si III. The experimental recombination rate coefficientswere measured in a merged-beam-type experiment at the heavy-ion storagering CRYRING at the Manne Siegbahn Laboratory in Stockholm. Changing theelectron–ion relative energy from 0 to 20 eV we covered the energy region fromthe first to the third ionization threshold. We find that even for the low-chargedSi2+ ion, a relativistic many-body perturbation theory calculation is necessary,to describe the recombination rate coefficients in the low-energy region, up to1.5 eV, satisfactorily. Doubly excited states, forbidden to form in LS coupling,are responsible for the most prominent dielectronic recombination resonances atlow energies and contribute with 40% to the strength. Several wide resonancesgive rise to a plateau-like formation in the recombination spectrum. A broaderenergy range, up to 6.7 eV, was covered with a non-relativistic many-bodycalculation. This range contains, in addition to 3pn resonances, severalresonances of the type 3dn, with the LS-forbidden 3d2 3F states giving riseto a strong, isolated peak at 2.976 eV. The NIST database lists eleven doublyexcited states of Si III with energy positions deviating considerably from ourdetermination. Since the listed lines are also not fully matching those with thelargest fluorescence yields it must be concluded that they are misidentified.

  • 45.
    Orban, Istvan
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Tashenov, Stanislav
    Stockholm University, Faculty of Science, Department of Physics.
    Ferro, Fabrizio
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Schuch, Reinhold
    Stockholm University, Faculty of Science, Department of Physics.
    Charge-state Selected Detection of Photons from Electron-Ion Interactions in an EBIT2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114Article in journal (Refereed)
    Abstract [en]

    A new approach provides charge-state selective recombination rate coefficients from TOF spectraof highly charged ions extracted from an EBIT. Experimentally derived dielectronic recombinationspectra are compared with results of relativistic many body perturbation theory calculations. Electronimpact excitation rate coefficients are also obtained from the experiment through the separationof the DR contribution in the X-ray spectra. The combination of TOF and X-ray measurementsoffers a powerful tool for the simultaneous extraction of atomic quantities for several charge states.

  • 46. Popsueva, V.
    et al.
    Nepstad, R.
    Birkeland, T.
    Førre, M.
    Hansen, J.P.
    Lindroth, E.
    Stockholm University, Faculty of Science, Department of Physics.
    Waltersson, E.
    Stockholm University, Faculty of Science, Department of Physics.
    Structure of lateral two-electron quantum dot molecules in electromagnetic fields2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 76, no 3, p. 035303-Article in journal (Refereed)
    Abstract [en]

    The energy levels of laterally coupled parabolic double quantum dots are calculated for varying interdot distances. Electron-electron interaction is shown to dominate the spectra: In the diatomic molecule limit of large interdot separation, the two nearly degenerate singlet and triplet ground states are followed by a narrow band of four singlet and four triplet states. The energy spacing between the ground state and the first band of excited states scales directly with the confinement strength of the quantum wells. Similar level separation and band structure are found when the double dot is exposed to a perpendicular magnetic field. Conversely, an electric field parallel to the interdot direction results in a strong level mixing and a narrow transition from a localized state to a covalent diatomic molecular state.

  • 47. Sabbar, M.
    et al.
    Heuser, S.
    Boge, R.
    Lucchini, M.
    Carette, Thomas
    Stockholm University, Faculty of Science, Department of Physics. Université Libre de Bruxelles, Belgium.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Gallmann, L.
    Cirelli, C.
    Keller, U.
    Resonance Effects in Photoemission Time Delays2015In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 115, no 13, article id 133001Article in journal (Refereed)
    Abstract [en]

    We present measurements of single-photon ionization time delays between the outermost valence electrons of argon and neon using a coincidence detection technique that allows for the simultaneous measurement of both species under identical conditions. The analysis of the measured traces reveals energy-dependent time delays of a few tens of attoseconds with high energy resolution. In contrast to photoelectrons ejected through tunneling, single-photon ionization can be well described in the framework of Wigner time delays. Accordingly, the overall trend of our data is reproduced by recent Wigner time delay calculations. However, besides the general trend we observe resonance features occurring at specific photon energies. These features have been qualitatively reproduced and identified by a calculation using the multiconfigurational Hartree-Fock method, including the influence of doubly excited states and ionization thresholds.

  • 48.
    Saelen, Lene
    et al.
    Department of physics and technology, University of Bergen, Norway.
    Waltersson, Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Hansen, J. P.
    Department of physics and technology, University of Bergen, Norway.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Fundamental gates for a strongly correlated two-electron quantum ring2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 3, p. 033303-Article in journal (Refereed)
    Abstract [en]

    We demonstrate that conditional as well as unconditional basic operations which are necessary for universal quantum gates can be performed with almost 100% fidelity within a strongly interacting two-electron quantum ring. Both sets of operations are based on a quantum control algorithm that optimizes a driving electromagnetic pulse for a given quantum gate. The demonstrated transitions occur on a time scale much shorter than typical decoherence times of the system.

  • 49.
    Selstø, Sølve
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Bengtsson, Jakob
    Stockholm University, Faculty of Science, Department of Physics.
    Solution of the Dirac equation for hydrogenlike systems exposed to intense electromagnetic pulses2009In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 79, no 4, p. 043418-Article in journal (Refereed)
    Abstract [en]

    The time-dependent Dirac equation is solved numerically and compared to the corresponding prediction of the nonrelativistic Schrödinger equation for hydrogenlike systems exposed to intense laser pulses. It is found that for a correct description of effects beyond the dipole approximation, virtual electron-positron pairs can be very important. Relativistic effects in the ionization dynamics of highly charged systems are studied.

  • 50. Skjerlie Simonsen, Aleksander
    et al.
    Kjellsson, Tor
    Stockholm University, Faculty of Science, Department of Physics.
    Forre, Morten
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Selsto, Solve
    Ionization dynamics beyond the dipole approximation induced by the pulse envelope2016In: Physical Review D, ISSN 2469-9926, Vol. 93, no 5, article id 053411Article in journal (Refereed)
    Abstract [en]

    When atoms and molecules are ionized by laser pulses of finite duration and increasingly high intensities, the validity of the much-used dipole approximation, in which the spatial dependence and magnetic component of the external field are neglected, eventually breaks down. We report that, when going beyond the dipole approximation for the description of atoms exposed to ultraviolet light, the spatial dependence of the pulse shape, the envelope, provides the dominant correction, while the spatial dependence of the carrier is negligible. We present a first-order beyond-dipole correction to the Hamiltonian which accounts exclusively for nondipole effects stemming from the carrier envelope of the pulse. We demonstrate by ab initio calculations for hydrogen that this approximation, which we refer to as the envelope approximation, reproduces the full interaction beyond the dipole approximation for absolute and differential observables and proves to be valid for a broad range of high-frequency fields. This is done both for the Schrodinger and the Dirac equation. Moreover, it is demonstrated that the envelope approximation provides an interaction-term which gives rise to faster numerical convergence in terms of partial waves compared to its exact counterpart.

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