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  • 1. Ackermann, M.
    et al.
    Ajello, M.
    Albert, A.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Bastieri, D.
    Bechtol, K.
    Bellazzini, R.
    Bloom, E. D.
    Bonamente, E.
    Borgland, A. W.
    Brandt, T. J.
    Bregeon, J.
    Brigida, M.
    Bruel, P.
    Buehler, R.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Caraveo, P. A.
    Cecchi, C.
    Charles, E.
    Chekhtman, A.
    Chiang, J.
    Ciprini, S.
    Claus, R.
    Cohen-Tanugi, J.
    Conrad, Jan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Cuoco, Alessandro
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Cutini, S.
    D'Ammando, F.
    de Palma, F.
    Dermer, C. D.
    Digel, S. W.
    do Couto e Silva, E.
    Drell, P. S.
    Drlica-Wagner, A.
    Dubois, R.
    Favuzzi, C.
    Fegan, S. J.
    Ferrara, E. C.
    Fortin, P.
    Fukazawa, Y.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Germani, S.
    Giglietto, N.
    Giroletti, M.
    Glanzman, T.
    Godfrey, G.
    Gomez-Vargas, G. A.
    Gregoire, T.
    Grenier, I. A.
    Grove, J. E.
    Guiriec, S.
    Gustafsson, M.
    Hadasch, D.
    Hayashida, M.
    Hayashi, K.
    Hou, X.
    Hughes, R. E.
    Johannesson, G.
    Johnson, A. S.
    Kamae, T.
    Knoedlseder, J.
    Kuss, M.
    Lande, J.
    Latronico, L.
    Lemoine-Goumard, M.
    Linden, T.
    Lionetto, A. M.
    Garde, M. Llena
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Longo, F.
    Loparco, F.
    Lovellette, M. N.
    Lubrano, P.
    Mazziotta, M. N.
    McEnery, J. E.
    Mitthumsiri, W.
    Mizuno, T.
    Monte, C.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Murgia, S.
    Naumann-Godo, M.
    Norris, J. P.
    Nuss, E.
    Ohsugi, T.
    Okumura, A.
    Orienti, M.
    Orlando, E.
    Ormes, J. F.
    Paneque, D.
    Panetta, J. H.
    Parent, D.
    Pavlidou, V.
    Pesce-Rollins, M.
    Pierbattista, M.
    Piron, F.
    Pivato, G.
    Raino, S.
    Rando, R.
    Reimer, A.
    Reimer, O.
    Roth, M.
    Sbarra, C.
    Schmitt, J.
    Sgro, C.
    Siegal-Gaskins, J.
    Siskind, E. J.
    Spandre, G.
    Spinelli, P.
    Strong, A. W.
    Suson, D. J.
    Takahashi, H.
    Tanaka, T.
    Thayer, J. B.
    Tibaldo, L.
    Tinivella, M.
    Torres, D. F.
    Tosti, G.
    Troja, E.
    Usher, T. L.
    Vandenbroucke, J.
    Vasileiou, V.
    Vianello, G.
    Vitale, V.
    Waite, A. P.
    Winer, B. L.
    Wood, K. S.
    Wood, M.
    Yang, Zhaoyu
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zimmer, Stephan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Komatsu, E.
    Anisotropies in the diffuse gamma-ray background measured by the Fermi LAT2012In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 85, no 8, article id 083007Article in journal (Refereed)
    Abstract [en]

    The contribution of unresolved sources to the diffuse gamma-ray background could induce anisotropies in this emission on small angular scales. We analyze the angular power spectrum of the diffuse emission measured by the Fermi Large Area Telescope at Galactic latitudes vertical bar b vertical bar > 30 degrees in four energy bins spanning 1-50 GeV. At multipoles l >= 155, corresponding to angular scales less than or similar to 2 degrees, angular power above the photon noise level is detected at >99.99% confidence level in the 1-2 GeV, 2-5 GeV, and 5-10 GeV energy bins, and at >99% confidence level at 10-50 GeV. Within each energy bin the measured angular power takes approximately the same value at all multipoles l >= 155, suggesting that it originates from the contribution of one or more unclustered source populations. The amplitude of the angular power normalized to the mean intensity in each energy bin is consistent with a constant value at all energies, C-P/< I >(2) 9.05 +/- 0.84 x 10(-6) sr, while the energy dependence of C-P is consistent with the anisotropy arising from one or more source populations with power-law photon spectra with spectral index Gamma(s) = 2.40 +/- 0.07. We discuss the implications of the measured angular power for gamma-ray source populations that may provide a contribution to the diffuse gamma-ray background.

  • 2.
    Adiels, L
    et al.
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Antonelli, A
    Backenstoss, G.
    Institute for Physics, University of Basle.
    Beltrami, I
    Bergström, I.
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Bloch, P
    Burgun, G
    DPhPe, CENSaclay.
    Carius, S.
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Chardalas, M
    Charalambous, S.
    Dept. of Nuclear Physics, Univerity of Tessaloniki.
    Dedoussis, S
    Derré, J
    Dousse, J. C.
    University of Fribourg.
    Dris, M
    Faure, J L
    Fetscher, W
    Fry, J R
    Filokyprou, G
    Gabathuler, Erwin
    Gamet, R
    Garreta, D
    Geralis, J
    Gerber, H J
    Guyot, C
    Hatzifotiadou, D.
    Hayman, P
    Hugi, M
    Institute for Physics, University of Basle.
    Kern, J
    Kerek, A.
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Kesseler, G
    Kochowski, Claude
    Kokinias, P
    Kostarakis, P
    Kuzminski, J
    Lefas, C
    Lindblad, T
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Mall, U
    Marel, Gérard
    Mason, P
    Milshtein, A I
    Nakada, Tatsuya
    Nilsson, A
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Papadopoulos, I M
    Pavlopoulos, P.
    Institute for Physics, University of Basle.
    Pauli, E
    Rickenbach, R
    Schaller, L A
    Schopper, A
    Tauscher, L.
    Institute for Physics, University of Basle.
    Tröster, D.
    Institute for Physics, University of Basle.
    Tzamouranis, Yu
    Watson, E. J.
    CERN.
    Zevgolatakos, S
    Study of CP violation in a tagged neutral kaon beam.1986In: Topical European Meeting on the Quark Structure of Matter in the Rhine Valley, 1986Conference paper (Other academic)
  • 3. Ai, Yue-jie
    et al.
    Tian, Guangjun
    Liao, Rong-zhen
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Zhang, Qiong
    Fang, Wei-hai
    Luo, Yi
    Intrinsic Property of Flavin Mononucleotide Controls its Optical Spectra in Three Redox States2011In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 12, no 16, p. 2899-2902Article in journal (Refereed)
  • 4.
    Ali, Safdar
    Stockholm University, Faculty of Science, Department of Physics.
    Electron - Ion Recombination Data for Plasma Applications: Results from Electron Beam Ion Trap and Ion Storage Ring2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis contains results of electron-ion recombination processes in atomic ions relevant for plasma applications. The measurements were performed at the Stockholm Refrigerated Electron Beam Ion Trap (R-EBIT) and at the CRYRING heavy-ion storage ring. Dielectronic recombination (DR) cross sections, resonant strengths, rate coefficients and energy peak positions in H-like and He-like S are obtained for the first time from the EBIT measurements. Furthermore, the experimentally obtained DR resonant strengths are used to check the behaviour of a scaling formula for low Z, H-and He-like iso-electronic sequences and to update the fitting parameters. KLL DR peak positions for initially He- to B-like Ar ions are obtained experimentally from the EBIT measurements. Both the results from highly charged sulfur and argon are compared with the calculations performed with a distorted wave approximation.

    Absolute recombination rate coefficients of B-like C, B-like Ne and Be-like F ions are obtained for the first time with high energy resolution from storage ring measurements. The experimental results are compared with the intermediate coupling AUTOSTRUCTURE calculations. Plasma rate coefficients of each of these ions are obtained by convoluting the energy dependent recombination spectra with a Maxwell-Boltzmann energy distribution in the temperature range of 103-106 K. The resulting plasma rate coefficients are presented and compared with the calculated data available in literature.

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  • 5.
    Ali, Safdar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Mahmood, Sultan
    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.
    Li, Y. M.
    Wu, Z.
    Schuch, Reinhold
    Stockholm University, Faculty of Science, Department of Physics.
    Electron-ion recombination of H- and He-like sulfur2011In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 44, no 22, p. 225203-Article in journal (Refereed)
    Abstract [en]

    Electron-ion recombination of sulfur ions with electrons in the energy range of 1.6-3 keV was studied at the Stockholm Refrigerated Electron Beam Ion Trap. We obtained the KLn dielectronic recombination (DR) cross sections up to n = 5 for H-like and He-like sulfur ions by observing the x-rays from the trapped ions. A fully relativistic distorted wave approximation method was used for calculating the DR cross sections, while the resonance energies were obtained with a multiconfiguration Dirac-Fock approach using the GRASP II code. The calculations agree with the experimental results within the experimental error bars. Additionally, the obtained total DR resonance strengths were used to check the behaviour of a scaling formula for low-Z, He-like iso-electronic sequence (Watanabe et al 2001 J. Phys. B: At. Mol. Opt. Phys. 34 5095).

  • 6.
    Ali, Safdar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Mahmood, Sultan
    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.
    Li, Y. M.
    Wu, Z.
    Schuch, Reinhold
    Stockholm University, Faculty of Science, Department of Physics.
    Photo-recombination studies at R-EBIT with a Labview control and data = quisition system2011In: Journal of Instrumentation, E-ISSN 1748-0221, Vol. 6, p. C01016-Article in journal (Refereed)
    Abstract [en]

    Equipment at the Stockholm Refrigerated Electron Beam Ion Trap (R-EBIT) was developed for photo-recombination studies. A LabView-based event mode data acquisition and R-EBIT control system was implemented. The energies of KLL dielectronic recombination resonances in Li- to C-like argon ions were determined and compared with theoretical calculations performed using a distorted wave approximation. The theoretical and experimental peak positions for Li-, Be-, and C-like argon ions agree within the error bars. For B-like argon we observe an energy shift of 9 eV between the experimentally obtained peak position and the calculated result.

  • 7.
    Amann-Winkel, Katrin
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Max Planck Institute for Polymer Research and Johannes Gutenberg University, Germany.
    Kim, Kyung Hwan
    Giovambattista, Nicolas
    Ladd-Parada, Marjorie
    Stockholm University, Faculty of Science, Department of Physics.
    Späh, Alexander
    Stockholm University, Faculty of Science, Department of Physics.
    Perakis, Fivos
    Stockholm University, Faculty of Science, Department of Physics.
    Pathak, Harshad
    Stockholm University, Faculty of Science, Department of Physics.
    Yang, Cheolhee
    Eklund, Tobias
    Stockholm University, Faculty of Science, Department of Physics.
    Lane, Thomas J.
    You, Seonju
    Jeong, Sangmin
    Lee, Jae Hyuk
    Eom, Intae
    Kim, Minseok
    Park, Jaeku
    Chun, Sae Hwan
    Poole, Peter H.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Liquid-liquid phase separation in supercooled water from ultrafast heating of low-density amorphous ice2023In: Nature Communications, E-ISSN 2041-1723, Vol. 14, no 1, article id 442Article in journal (Refereed)
    Abstract [en]

    Recent experiments continue to find evidence for a liquid-liquid phase transition (LLPT) in supercooled water, which would unify our understanding of the anomalous properties of liquid water and amorphous ice. These experiments are challenging because the proposed LLPT occurs under extreme metastable conditions where the liquid freezes to a crystal on a very short time scale. Here, we analyze models for the LLPT to show that coexistence of distinct high-density and low-density liquid phases may be observed by subjecting low-density amorphous (LDA) ice to ultrafast heating. We then describe experiments in which we heat LDA ice to near the predicted critical point of the LLPT by an ultrafast infrared laser pulse, following which we measure the structure factor using femtosecond x-ray laser pulses. Consistent with our predictions, we observe a LLPT occurring on a time scale < 100 ns and widely separated from ice formation, which begins at times >1 μs.

  • 8.
    Amselem, Elias
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Bourennane, Mohamed
    Stockholm University, Faculty of Science, Department of Physics.
    Reply to 'Experimental bound entanglement?'2010In: Nature Physics, ISSN 1745-2473, E-ISSN 1745-2481, Vol. 6, p. 827-827Article in journal (Other (popular science, discussion, etc.))
  • 9.
    Amselem, Elias
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Bourennane, Mohamed
    Stockholm University, Faculty of Science, Department of Physics.
    Cabello, Adán
    Departamento de Física Aplicada II, Universidad de Sevilla.
    Danielsen, Lars Eirik
    Department of Informatics, University of Bergen.
    López-Tarrida, Antonio
    Departamento de Física Aplicada II, Universidad de Sevilla.
    Portillo, José
    Departamento de Matemática Aplicada I, Universidad de Sevilla.
    Experimental fully contextual correlationsArticle in journal (Refereed)
    Abstract [en]

    Quantum correlations are contextual yet, in general, nothing prevents the existence of even morecontextual correlations. We identify and test a simple noncontextual inequality in which the quantumviolation cannot be improved by any hypothetical post-quantum resource, and use it to experimentally obtain correlations in which the maximum noncontextual content, defined as the maximumfraction of noncontextual correlations, is less than 0.06. Our correlations are experimentally generated from the outcomes of sequential compatible measurements on a four-state quantum system encoded in the polarization and path of a single photon.

  • 10.
    Amselem, Elias
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Sadiq, Muhamad
    Stockholm University, Faculty of Science, Department of Physics.
    Bourennane, Mohamed
    Stockholm University, Faculty of Science, Department of Physics.
    Experimental bound entanglement through a Pauli channel2013In: Scientific Reports, E-ISSN 2045-2322, Vol. 3, article id 1966Article in journal (Refereed)
    Abstract [en]

    Understanding the characteristics of a quantum systems when affected by noise is one of the biggest challenges for quantum technologies. The general Pauli error channel is an important lossless channel for quantum communication. In this work we consider the effects of a Pauli channel on a pure four-qubit state and simulate the Pauli channel experimentally by studying the action on polarization encoded entangled photons. When the noise channel acting on the photons is correlated, a set spanned by four orthogonal bound entangled states can be generated. We study this interesting case experimentally and demonstrate that products of Bell states can be brought into a bound entangled regime. We find states in the set of bound entangled states which experimentally violate the CHSH inequality while still possessing a positive partial transpose.

  • 11.
    Anderson, Emma
    Stockholm University, Faculty of Science, Department of Physics.
    The Curious Case of Hot Metal Clusters: Spontaneous decay of excited, small silver and copper cluster anions in DESIREE2018Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Clusters anions are complex systems which, when formed with high internal energies, can decay via fragmentation and/or electron loss and may also cool via photon emission (radiative cooling). By studying the spontaneous decay mechanisms of small metal clusters, we can gain insight into the structure and properties of these systems. Whilst the qualitative behaviour of clusters in general can be described with statistical methods the properties of smallclusters depend strongly on the number of constituents. A detailed understanding of how the structure and energetics of such systems drive the cooling processes is yet to be found.

    This thesis presents measurements of the spontaneous decay of vibrationally excited small silver (Agn= 2-7) and copper clusters (Cun= 3-6). These measurements were performed using a single ring of the Double ElectroStatic Ion Ring ExpEriment (DESIREE) in which ions are stored in a cryogenic (~13 K) and extreme vacuum (10-14mbar) environment. The storage conditions of DESIREE enable the spontaneous decay of the silver and copper cluster anions to be followed to long time scales of up to 60 s. These long times were inaccessible until the recent development of cryogenic ion storage rings and traps. Theoretical calculations of the decay of the cluster anions were performed using a detailed balance method and these are presented and compared to the measured decay curves. Furthermore, the present measurements are compared to existing experimental results.

  • 12.
    Anderson, Emma K.
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Aarhus University, Denmark.
    Schmidt-May, Alice Frederike
    Stockholm University, Faculty of Science, Department of Physics.
    Najeeb, P. K.
    Stockholm University, Faculty of Science, Department of Physics.
    Eklund, Gustav
    Stockholm University, Faculty of Science, Department of Physics.
    Chartkunchand, K. C.
    Rosén, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    Kamińska, Magdalena
    Stockholm University, Faculty of Science, Department of Physics.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Nascimento, R.
    Hansen, K.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Fragmentation of and electron detachment from hot copper and silver dimer anions: A comparison2023In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 107, no 6, article id 062824Article in journal (Refereed)
    Abstract [en]

    We measured the spontaneous decays of internally hot copper and silver dimer anions, and , stored in one of the two ion-beam storage rings of the Double Electrostatic Ion Ring Experiment (DESIREE) at Stockholm University. A coincidence detection technique was utilized enabling essentially background-free measurements of -> Cu + Cu- and -> Ag + Ag- fragmentation rates. Furthermore, the total rates of neutral decay products (monomers and dimers) were measured and the relative contributions of fragmentation and electron emission ( -> Cu2 + e- and -> Ag2 + e-) were deduced as functions of storage time. Fragmentation is completely dominant at early times. However, after about 20 ms of storage, electron emission is observed and becomes the leading decay path after 100 ms for both dimer anions. The branching ratios between fragmentation and electron emission (vibrationally assisted autodetachment processes) are very nearly the same for and Ag-2 throughout the present storage cycle of 10 seconds. This is surprising considering the difference between the electron affinities of the neutral dimers, Cu2 and Ag2, and the difference between the and the dissociation energies.

  • 13.
    Andersson, Arne J. W.
    Stockholm University.
    Simulation techniques applied to nuclear reactor technology1973Doctoral thesis, comprehensive summary (Other academic)
  • 14.
    Andersson, David
    Stockholm University, Faculty of Science, Department of Physics.
    Thermal effects and spontaneous frictional relaxation in atomically thin layered materialsManuscript (preprint) (Other academic)
  • 15. Andersson, E
    et al.
    Stenrup, M
    Eland, J H D
    Hedin, L
    Berglund, M
    Karlsson, L
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Ågren, H
    Rubensson, J. -E.
    Feifel, R
    Single-photon core-valence double ionization of molecular oxygen2008In: Phys. Rev. A, Vol. 78, p. 023409-Article in journal (Refereed)
    Abstract [en]

    Single-photon core-valence double ionization of molecular oxygen has been studied using a magnetic bottle time-of-flight electron coincidence spectrometer. The K−1V−1 double ionization electron spectrum of O2 is reported and is assigned with the aid of ab initio calculations. A direct comparison of the core-valence double ionization electron spectra with the conventional valence band photoelectron spectrum is made. The lowest core-valence double ionization energy is found to be 571.6 eV and is associated with a 3 dicationic state.

  • 16.
    Andersson, Julius
    Stockholm University, Faculty of Science, Department of Physics.
    Laser cooling, state initialization and laser manipulation of a trapped ion2021Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    One way of realizing a quantum computer is to use an ion trap. The research group Trapped Ion Quantum Technologies at Stockholm university were operating an ion trap with strontium ions. To increase the coherence time they installed a magnetic field shielding. Therefore the experimental setup had to be partially rebuilt. A new 405 nm laser was installed in order to speed up the ionization step of neutral strontium atoms. The characterization of the laser was performed and it showed that the laser could be operated at the required wavelength. The wavelength was characterized with respect to temperature and power. A scan of the 422 nm Doppler cooling laser was also performed and it showed that the Doppler cooling worked as intended. Lastly, Rabi oscillations were performed to see if coherent manipulation of the ion's quantum state worked as intended. This experiment was also successful but it showed some differences between having the magnetic shielding door open or closed which should be investigated further.

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  • 17.
    Andersson, Ole
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Bengtsson, Ingemar
    Stockholm University, Faculty of Science, Department of Physics.
    Ericsson, Marie
    Sjöqvist, Erik
    Geometric phases for mixed states of the Kitaev chain2016In: Philosophical Transactions. Series A: Mathematical, physical, and engineering science, ISSN 1364-503X, E-ISSN 1471-2962, Vol. 374, no 2068, article id 20150231Article in journal (Refereed)
    Abstract [en]

    The Berry phase has found applications in building topological order parameters for certain condensed matter systems. The question whether some geometric phase for mixed states can serve the same purpose has been raised, and proposals are on the table. We analyse the intricate behaviour of Uhlmann's geometric phase in the Kitaev chain at finite temperature, and then argue that it captures quite different physics from that intended. We also analyse the behaviour of a geometric phase introduced in the context of interferometry. For the Kitaev chain, this phase closely mirrors that of the Berry phase, and we argue that it merits further investigation.

  • 18. Andersson, Renée
    et al.
    Kadi, Malin
    Davidsson, Jan
    Hansson, Tony
    Stockholm University, Faculty of Science, Department of Physics.
    Photoionisation of molecular wavepackets – the NaK(C1Σ+) case2002In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 352, no 1-2, p. 106-112Article in journal (Refereed)
  • 19.
    Andersson, Sten
    Stockholm University.
    Aspects on the problems of synthesis and structure of some oxide or oxide-like compounds formed by the transition elements in the groups 4, 5 and 6 of the periodic table.1967Doctoral thesis, comprehensive summary (Other academic)
  • 20. Andresen, G. B.
    et al.
    Ashkezari, M. D.
    Baquero-Ruiz, M.
    Bertsche, W.
    Bowe, P. D.
    Butler, E.
    Cesar, C. L.
    Chapman, S.
    Charlton, M.
    Deller, A.
    Eriksson, S.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Gutierrez, A.
    Hangst, J. S.
    Hardy, W. N.
    Hayden, M. E.
    Humphries, A. J.
    Hydomako, R.
    Jenkins, M. J.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Jorgensen, L. V.
    Kurchaninov, L.
    Madsen, N.
    Menary, S.
    Nolan, P.
    Olchanski, K.
    Olin, A.
    Povilus, A.
    Pusa, P.
    Robicheaux, F.
    Sarid, E.
    Nasr, S. Seif el
    Silveira, D. M.
    So, C.
    Storey, J. W.
    Thompson, R. I.
    van der Werf, D. P.
    Wurtele, J. S.
    Yamazaki, Y.
    Trapped antihydrogen2010In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 468, no 7324, p. 673-676Article in journal (Refereed)
    Abstract [en]

    Antimatter was first predicted1 in 1931, by Dirac. Work with high-energy antiparticles is now commonplace, and anti-electrons are used regularly in the medical technique of positron emission tomography scanning. Antihydrogen, the bound state of an antiproton and a positron, has been produced2, 3 at low energies at CERN (the European Organization for Nuclear Research) since 2002. Antihydrogen is of interest for use in a precision test of nature’s fundamental symmetries. The charge conjugation/parity/time reversal (CPT) theorem, a crucial part of the foundation of the standard model of elementary particles and interactions, demands that hydrogen and antihydrogen have the same spectrum. Given the current experimental precision of measurements on the hydrogen atom (about two parts in 1014 for the frequency of the 1s-to-2s transition4), subjecting antihydrogen to rigorous spectroscopic examination would constitute a compelling, model-independent test of CPT. Antihydrogen could also be used to study the gravitational behaviour of antimatter5. However, so far experiments have produced antihydrogen that is not confined, precluding detailed study of its structure. Here we demonstrate trapping of antihydrogen atoms. From the interaction of about 107 antiprotons and 7 × 108 positrons, we observed 38 annihilation events consistent with the controlled release of trapped antihydrogen from our magnetic trap; the measured background is 1.4 ± 1.4 events. This result opens the door to precision measurements on anti-atoms, which can soon be subjected to the same techniques as developed for hydrogen.

  • 21. Andresen, G. B.
    et al.
    Ashkezari, M. D.
    Baquero-Ruiz, M.
    Bertsche, W.
    Bowe, P. D.
    Butler, E.
    Cesar, C. L.
    Chapman, S.
    Charlton, M.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Hangst, J. S.
    Hardy, W. N.
    Hayano, R. S.
    Hayden, M. E.
    Humphries, A.
    Hydomako, R.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Kurchaninov, L.
    Lambo, R.
    Madsen, N.
    Menary, S.
    Nolan, P.
    Olchanski, K.
    Olin, A.
    Povilus, A.
    Pusa, P.
    Robicheaux, F.
    Sarid, E.
    Silveira, D. M.
    So, C.
    Storey, J. W.
    Thompson, R. I.
    van der Werf, D. P.
    Wilding, D.
    Wurtele, J. S.
    Yamazaki, Y.
    Evaporative Cooling of Antiprotons to Cryogenic Temperatures2010In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 105, no 1, p. 013003-Article in journal (Refereed)
    Abstract [en]

    We report the application of evaporative cooling to clouds of trapped antiprotons, resulting in plasmas with measured temperature as low as 9 K. We have modeled the evaporation process for charged particles using appropriate rate equations. Good agreement between experiment and theory is observed, permitting prediction of cooling efficiency in future experiments. The technique opens up new possibilities for cooling of trapped ions and is of particular interest in antiproton physics, where a precise CPT test on trapped antihydrogen is a long-standing goal.

  • 22. Araujo, Mateus
    et al.
    Quintino, Marco Tulio
    Cavalcanti, Daniel
    Santos, Marcelo Franca
    Cabello, Adan
    Stockholm University, Faculty of Science, Department of Physics.
    Cunha, Marcelo Terra
    Tests of bell inequality with arbitrarily low photodetection efficiency and homodyne measurements2012In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 86, no 3, p. 030101-Article in journal (Refereed)
    Abstract [en]

    We show that hybrid local measurements combining homodyne measurements and photodetection provide violations of a Bell inequality with arbitrarily low photodetection efficiency. This is shown in two different scenarios: when one part receives an atom entangled to the field mode to be measured by the other part and when both parts make similar photonic measurements. Our findings promote the hybrid measurement scenario as a candidate for loophole-free Bell tests beyond previous expectations.

  • 23. Argenti, Luca
    et al.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Attosecond photoelectron spectroscopy of helium doubly excited states2023In: Physical Review Research, E-ISSN 2643-1564, Vol. 5, no 3, article id 033047Article in journal (Refereed)
    Abstract [en]

    We describe a numerical method that simulates the interaction of the helium atom with sequences of femtosecond and attosecond light pulses. The method, which is based on the close-coupling expansion of the electronic configuration space in a B-spline bipolar spherical harmonic basis, can accurately reproduce the excitation and single ionization of the atom, within the electrostatic approximation. The time-dependent Schrödinger equation is integrated with a sequence of second-order split-exponential unitary propagators. The asymptotic channel-, energy-, and angularly resolved photoelectron distributions are computed by projecting the wave packet at the end of the simulation on the multichannel scattering states of the atom, which are separately computed within the same close-coupling basis. This method is applied to simulate the pump-probe ionization of helium in the vicinity of the 2s/2p excitation threshold of the He+ ion. This work confirms the qualitative conclusions of one of our earliest publications [Argenti and Lindroth, Phys. Rev. Lett. 105, 053002 (2010)], in which we demonstrated the control of the 2s/2p ionization branching ratio. Here we take those calculations to convergence and show how correlation brings the periodic modulation of the branching ratios in almost phase opposition. The residual total ionization probability to the 2s+2p channels is dominated by the beating between the sp+2,3 and the sp+2,4 doubly excited states, which is consistent with the modulation of the complementary signal in the 1s channel, measured in 2010 by Chang and coworkers [Gilbertson et al., Phys. Rev. Lett. 105, 263003 (2010)].

  • 24.
    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.

  • 25. 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.

  • 26. Artesani, Alessia
    et al.
    Lamuraglia, Raffaella
    Menegazzo, Federica
    Bonetti, Stefano
    Stockholm University, Faculty of Science, Department of Physics. Istituto Italiano di Tecnologia, Italy; Ca' Foscari University of Venice, Italy .
    Traviglia, Arianna
    Terahertz Time-Domain Spectroscopy in Reflection Configuration for Inorganic and Mineral Pigment Identification2023In: Applied Spectroscopy, ISSN 0003-7028, E-ISSN 1943-3530, Vol. 77, no 1, p. 74-87Article in journal (Refereed)
    Abstract [en]

    This work demonstrates terahertz time-domain spectroscopy (THz-TDS) in reflection configuration on a class of inorganic and mineral pigments. The technique is validated for pictorial materials against the limitations imposed by the back-reflection of the THz signal, such as weak signal intensity, multiple signal losses and distortion, as well as the current scarce databases. This work provides a detailed description of the experimental procedure and method used for the determination of material absorption coefficient of a group of 10 pigments known to be used in ancient frescoes, that are, Cu-based (azurite, malachite, and Egyptian blue), Pb-based (minium and massicot), Fe-based (iron oxide yellow, dark ochre, hematite, and Pompeii red) pigments and mercury sulfide (cinnabar), and classified the vibrational modes of the molecular oxides and sulfides for material identification. The results of this work showed that the mild signal in reflection configuration does not limit the application of THz-TDS on inorganic and mineral pigments as long as (i) the THz signal is normalized with a highly reflective reference sample, (ii) the secondary reflected signals from inner interfaces are removed with a filtering procedure, and (iii) the limitations at high frequencies imposed by the dynamic range of the instrument are considered. Under these assumptions, we were able to differentiate molecular phases of the same metal and identify azurite, Egyptian blue, minium, and cinnabar, isolating the molecular vibrations up to 125 cm−1. The established approach demonstrated to be reliable, and it can be extended for the study of other materials, well beyond the reach of the heritage domain. 

  • 27. Artesani, Alessia
    et al.
    Ljubenovic, Marina
    Traviglia, Arianna
    Bonetti, Stefano
    Stockholm University, Faculty of Science, Department of Physics. Ca'Foscari University of Venice, Italy.
    Self-Referenced Method for Geometrical Distortion Removal in THz Time-Domain Reflection Imaging2023In: IEEE Transactions on Terahertz Science and Technology, ISSN 2156-342X, E-ISSN 2156-3446, Vol. 13, no 2, p. 113-121Article in journal (Refereed)
    Abstract [en]

    In this article, we develop a method for removing the phase drift induced by physically distorted object in terahertz time-domain reflection imaging (THz-TDRI). The proposed approach is defined as self-referenced, as it does not rely on any numerical parameter optimization nor extra instrumental components, and it is based on the unique manipulation of time-domain imaging data. In fact, we demonstrate that the problem can be solved assuming a linear contribution of the temporal shift induced by surface curvature. We illustrate how the self-referenced method is modeled and implemented, and we report the results obtained on two objects with different characteristics: a tilted and highly reflective surface, and a warped and heterogeneous surface. The proposed method demonstrates how to successfully remove the phase alterations induced on the reflected electric field, and how to repair the heavily corrupted images in the frequency-domain.

  • 28. Ashworth, Eleanor K.
    et al.
    Langeland, Jeppe
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Toft Lindkvist, Thomas
    Kjær, Christina
    Bull, James N.
    Brøndsted Nielsen, Steen
    Cryogenic Fluorescence Spectroscopy of Ionic Fluorones in Gaseous and Condensed Phases: New Light on Their Intrinsic Photophysics2022In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 126, no 51, p. 9553-9563Article in journal (Refereed)
    Abstract [en]

    Fluorescence spectroscopy of gas-phase ions generated through electrospray ionization is an emerging technique able to probe intrinsic molecular photophysics directly without perturbations from solvent interactions. While there is ample scope for the ongoing development of gas-phase fluorescence techniques, the recent expansion into low-temperature operating conditions accesses a wealth of data on intrinsic fluorophore photophysics, offering enhanced spectral resolution compared with room-temperature measurements, without matrix effects hindering the excited-state dynamics. This perspective reviews current progress on understanding the photophysics of anionic fluorone dyes, which exhibit an unusually large Stokes shift in the gas phase, and discusses how comparison of gas- and condensed-phase fluorescence spectra can fingerprint structural dynamics. The capacity for temperature-dependent measurements of both fluorescence emission and excitation spectra helps establish the foundation for the use of fluorone dyes as fluorescent tags in macromolecular structure determination. We suggest ideas for technique development. 

  • 29. Ashworth, Eleanor K.
    et al.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Kjaer, Christina
    Page, Philip C. Bulman
    Meech, Stephen R.
    Nielsen, Steen Brondsted
    Bull, James N.
    Complexation of Green and Red Kaede Fluorescent Protein Chromophores by a Zwitterion to Probe Electrostatic and Induction Field Effects2022In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 126, no 7, p. 1158-1167Article in journal (Refereed)
    Abstract [en]

    The photophysics of green fluorescent protein (GFP) and red Kaede fluorescent protein (rKFP) are defined by the intrinsic properties of the light-absorbing chromophore and its interaction with the protein binding pocket. This work deploys photodissociation action spectroscopy to probe the absorption profiles for a series of synthetic GFP and rKFP chromophores as the bare anions and as complexes with the betaine zwitterion, which is assumed as a model for dipole microsolvation. Electronic structure calculations and energy decomposition analysis using Symmetry-Adapted Perturbation Theory are used to characterize gas-phase structures and complex cohesion forces. The calculations reveal a preponderance for coordination of betaine to the phenoxide deprotonation site predominantly through electrostatic forces. Calculations using the STEOM-DLPNO-CCSD method are able to reproduce absolute and relative vertical excitation energies for the bare anions and anion–betaine complexes. On the other hand, treatment of the betaine molecule with a point-charge model, in which the charges are computed from some common electron density population analysis schemes, show that just electrostatic and point-charge induction interactions are unable to account for the betaine-induced spectral shift. The present methodology could be applied to investigate cluster forces and optical properties in other gas-phase ion–zwitterion complexes. 

  • 30. Baeuml, Lena
    et al.
    Rott, Florian
    Schnappinger, Thomas
    Stockholm University, Faculty of Science, Department of Physics. LMU Munich, Germany.
    de Vivie-Riedle, Regina
    Following the Nonadiabatic Ultrafast Dynamics of Uracil via Simulated X-ray Absorption Spectra2023In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 127, no 46, p. 9787-9796Article in journal (Refereed)
    Abstract [en]

    The nucleobase uracil exhibits high photostability due to ultrafast relaxation processes mediated by conical intersections (CoIns), where the interplay between nuclear and electron dynamics becomes crucial. In our previous study, we observed seemingly long-lived traces of electronic coherence for the relaxation process through the S-2/S-1 CoIn by applying our ansatz for coupled nuclear and electron dynamics in molecules (NEMol). In this work, we theoretically investigate how time-dependent transient X-ray absorption spectroscopy can be used to observe this ultrafast dynamics. Therefore, we calculated X-ray absorption spectra (XAS) for the oxygen K-edge, using a multireference protocol in combination with NEMol dynamics. Thus, we have access to both the transient XAS based on the nuclear wavepacket dynamics and the modulation of the signals caused by the electronic coherence induced by the excitation process and the presence of a CoIn seam. In both cases, we were able to qualitatively predict its influence on the resulting XAS.

  • 31.
    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.

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    PhysRevA.85.013415.pdf
  • 32.
    Banerjee, Ambar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Coates, Michael R.
    Stockholm University, Faculty of Science, Department of Physics.
    Kowalewski, Markus
    Stockholm University, Faculty of Science, Department of Physics.
    Wikmark, Hampus
    Jay, Raphael M.
    Wernet, Philippe
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Photoinduced bond oscillations in ironpentacarbonyl give delayed synchronous bursts of carbonmonoxide release2022In: Nature Communications, E-ISSN 2041-1723, Vol. 13, no 1, article id 1337Article in journal (Refereed)
    Abstract [en]

    Early excited state dynamics in the photodissociation of transition metal carbonyls determines the chemical nature of short-lived catalytically active reaction intermediates. However, time-resolved experiments have not yet revealed mechanistic details in the sub-picosecond regime. Hence, in this study the photoexcitation of ironpentacarbonyl Fe(CO)5 is simulated with semi-classical excited state molecular dynamics. We find that the bright metal-to-ligand charge-transfer (MLCT) transition induces synchronous Fe-C oscillations in the trigonal bipyramidal complex leading to periodically reoccurring release of predominantly axial CO. Metaphorically the photoactivated Fe(CO)5 acts as a CO geyser, as a result of dynamics in the potential energy landscape of the axial Fe-C distances and non-adiabatic transitions between manifolds of bound MLCT and dissociative metal-centered (MC) excited states. The predominant release of axial CO ligands and delayed release of equatorial CO ligands are explained in a unified mechanism based on the σ*(Fe-C) anti-bonding character of the receiving orbital in the dissociative MC states.

  • 33.
    Banerjee, Ambar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    da Cruz, Vinicius Vaz
    Ekholm, Victor
    Sathe, Conny
    Rubensson, Jan-Erik
    Ignatova, Nina
    Gel'mukhanov, Faris
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Simulating fluorine K-edge resonant inelastic x-ray scattering of sulfur hexafluoride and the effect of dissociative dynamics2023In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 108, no 2, article id 023103Article in journal (Refereed)
    Abstract [en]

    We report on a computational study of resonant inelastic x-ray scattering (RIXS), at different fluorine K-edge resonances of the SF6 molecule, and corresponding nonresonant x-ray emission. Previously measured polarization dependence in RIXS is reproduced and traced back to the local sigma and pi symmetry of the molecular orbitals and corresponding states involved in the RIXS process. Also electron-hole coupling energies are calculated and related to experimentally observed spectator shifts. The role of dissociative S-F bond dynamics is explored to model detuning of RIXS spectra at the |F1s(-1) 6a(1g)(1)> resonance, which shows challenges to accurately reproduce the required steepness for core-excited potential energy surface. We show that the RIXS spectra can only be properly described by considering breaking of the global inversion symmetry of the electronic wave function and core-hole localization, induced by vibronic coupling. Due to the core-hole localization we have symmetry forbidden transitions, which lead to additional resonances and changing width of the RIXS profile.

  • 34. Barklem, Paul S
    et al.
    Amarsi, Anish M
    Grumer, Jon
    Eklund, Gustav
    Stockholm University, Faculty of Science, Department of Physics.
    Rosén, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    Ji, MingChao
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T
    Stockholm University, Faculty of Science, Department of Physics.
    Mutual neutralisation in Li++H/D and Na++H/D collisions: Implications of experimentalresults for non-LTE modelling of stellar spectraManuscript (preprint) (Other academic)
  • 35.
    Baym, Gordon
    et al.
    Univ Illinois, Dept Phys, Urbana, IL , USA.
    Pethick, Christopher
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Univ Copenhagen, Niels Bohr Int Acad, Niels Bohr Inst, Copenhagen , Denmark.
    Normal mass density of a superfluid Fermi gas at unitarity2013In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 88, no 4, p. 043631-Article in journal (Refereed)
    Abstract [en]

    We calculate the normal mass density of a paired Fermi gas at unitarity. The dominant contribution near the superfluid transition is from fermionic quasiparticle excitations and is, thus, sensitive to the pairing gap. A comparison with the recent experiment of Sidorenkov et al. [Nature (London) 498, 78 (2013)] suggests that the superfluid gap near the transition temperature is larger than the BCS value, but the data do not permit a quantitative inference of the gap. Calculations of the quenched moment of inertia of a BCS superfluid in a harmonic trap are in reasonable agreement with the earlier experiment of Riedl et al.

  • 36. Behringer, Hans
    et al.
    Eichhorn, Ralf
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Brownian dynamics simulations with hard-body interactions: Spherical particles2012In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 137, no 16, p. 164108-Article in journal (Refereed)
    Abstract [en]

    A novel approach to account for hard-body interactions in (overdamped) Brownian dynamics simulations is proposed for systems with non-vanishing force fields. The scheme exploits the analytically known transition probability for a Brownian particle on a one-dimensional half-line. The motion of a Brownian particle is decomposed into a component that is affected by hard-body interactions and into components that are unaffected. The hard-body interactions are incorporated by replacing the affected component of motion by the evolution on a half-line. It is discussed under which circumstances this approach is justified. In particular, the algorithm is developed and formulated for systems with space-fixed obstacles and for systems comprising spherical particles. The validity and justification of the algorithm is investigated numerically by looking at exemplary model systems of soft matter, namely at colloids in flow fields and at protein interactions. Furthermore, a thorough discussion of properties of other heuristic algorithms is carried out.

  • 37.
    Bengtsson, Ingemar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Blanchfield, Kate
    Stockholm University, Faculty of Science, Department of Physics.
    Cabello, Adán
    Stockholm University, Faculty of Science, Department of Physics. Universidad de Sevilla, Spain.
    A Kochen-Specker inequality for a SIC2012In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 376, no 4, p. 374-376Article in journal (Refereed)
    Abstract [en]

    Yu and Oh (eprint) [1] have given a state-independent proof of the Kochen–Specker theorem in three dimensions using only 13 rays. The proof consists of showing that a non-contextual hidden variable theory necessarily leads to an inequality that is violated by quantum mechanics. We give a similar proof making use of 21 rays that constitute aSIC (symmetric informationally-complete positive operator-valued measure) and a complete set of MUB (mutually unbiased bases). A theory-independent inequality is also presented using the same 21 rays, as required for experimental tests of contextuality.

  • 38.
    Bengtsson, Jakob
    Stockholm University, Faculty of Science, Department of Physics.
    On the use of the uniform complex scaling-method for studying time-dependent systems2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    During the last few decades, laser technology has gone through a series of revolutionary improvements. With light pulses in the sub-femtosecond regime now experimentally available, an explicit time-dependent Hamilton operator is indispensable for a proper theoretical description of the interactions of atoms with such pulses. However, these theoretical studies are computationally very demanding, which motivates the search for new numerical methods and algorithms to approach time-dependent problems. This thesis contributes to this research field, with the main focus on the use of complex-scaled Hamilton operators. Thus, the formalism of complex scaling is studied in the context of its application to explicitly time-dependent atomic systems.

    Both non-relativistic and relativistic dynamics are investigated. The numerical advantages and the possibilities to extract physical quantities from complex-scaled wave functions are discussed. Of special interest is the ability to treat resonance states. These are multiply excited electronic states with sufficient energy to decay through Auger transitions to the surrounding continuum. With complex scaling, the Hamilton operator is non-Hermitian and such resonance states can be obtained as eigenstates.

    To analyze the non-bound part of the wave function requires essentially the construction of a second wave function; the left state vector. This additional wave function is, however, not easily constructed numerically in the complex scaling-method. To circumvent some of the numerical problems, we have proposed three different methods. These methods are based on Floquet theory, a propagation on a complex time-grid and time-dependent perturbation theory. By carefully investigating the numerical properties of the left state vector, we have thus studied the non-bound part of the system.

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    fulltext
  • 39.
    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.

  • 40.
    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.

  • 41.
    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.

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    fulltext
  • 42. Berggren, A. -M
    et al.
    Aldahan, A.
    Possnert, G.
    Hansson, Margareta
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Steen-Larsen, H. C.
    Storm, A. Sturevik
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Murad, A.
    Variability of Be-10 and delta O-18 in snow pits from Greenland and a surface traverse from Antarctica2013In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 294, p. 568-572Article in journal (Refereed)
    Abstract [en]

    To examine temporal variability of Be-10 in glacial ice, we sampled snow to a depth of 160 cm at the NEEM (North Greenland Eemian Ice Drilling) drilling site in Greenland. The samples span three years between the summers of 2006 and 2009. At the same time, spatial variability of Be-10 in glacial ice was explored through collection of the upper similar to 5 cm of surface snow in Antarctica during part of the Swedish-Japanese traverse from Svea to Syowa station during the austral summer in 2007-2008. The results of the Greenlandic 1 Be snow suggested variable concentrations that apparently do not clearly reflect the seasonal change as indicated by the delta O-18 data. The Be-10 concentration variability most likely reflects also effects of aerosol loading and deposition pathways, possibly in combination with post-depositional processes. The Antarctic traverse data expose a negative correlation between Be-10 and delta O-18, while there are weaker but still significant correlations to altitude and distance to the coast (approximated by the distance to the 70th latitude). These relationships indicate that geographical factors, mainly the proximity to the coast, may strongly affect 1 Be concentrations in snow in Queen Maud Land, Antarctica.

  • 43.
    Bergqvist, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Light transport and positioning simulations for the design of a cylindrical SPECT camera1998Doctoral thesis, comprehensive summary (Other academic)
  • 44.
    Berkowicz, Sharon
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Das, Sudipta
    Stockholm University, Faculty of Science, Department of Physics.
    Reiser, Mario
    Stockholm University, Faculty of Science, Department of Physics.
    Filianina, Mariia
    Stockholm University, Faculty of Science, Department of Physics.
    Bin, Maddalena
    Stockholm University, Faculty of Science, Department of Physics.
    Crevatin, Giulio
    Hennies, Franz
    Weninger, Clemens
    Björling, Alexander
    Bell, Paul
    Perakis, Fivos
    Stockholm University, Faculty of Science, Department of Physics.
    Nanofocused x-ray photon correlation spectroscopy2022In: Physical Review Research, E-ISSN 2643-1564, Vol. 4, no 3, article id L032012Article in journal (Refereed)
    Abstract [en]

    Here, we demonstrate an experimental proof of concept for nanofocused x-ray photon correlation spectroscopy, a technique sensitive to nanoscale fluctuations present in a broad range of systems. The experiment, performed at the NanoMAX beamline at MAX IV, uses a novel event-based x-ray detector to capture nanoparticle structural dynamics with microsecond resolution. By varying the nanobeam size from σ=88 nm to σ=2.5μm, we quantify the effect of the nanofocus on the small-angle scattering lineshape and on the diffusion coefficients obtained from nano-XPCS. We observe that the use of nanobeams leads to a multifold increase in speckle contrast, which greatly improves the experimental signal-to-noise ratio, quantified from the two-time intensity correlation functions. We conclude that it is possible to account for influence of the high beam divergence on the lineshape and measured dynamics by including a convolution with the nanobeam profile in the model.

  • 45. Bernard, Jérôme
    et al.
    Ji, MingChao
    Stockholm University, Faculty of Science, Department of Physics.
    Indrajith, Suvasthika
    Stockholm University, Faculty of Science, Department of Physics.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Navarro-Navarrete, José E.
    Stockholm University, Faculty of Science, Department of Physics.
    Kono, Naoko
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Martin, Serge
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Efficient radiative cooling of tetracene cations C18H12+: absolute recurrent fluorescence rates as a function of internal energy2023In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 25, no 15, p. 10726-10740Article in journal (Refereed)
    Abstract [en]

    We have measured recurrent fluorescence (RF) cooling rates of internally hot tetracene cations, C18H12+, as functions of their storage times and internal energies in two different electrostatic ion-beam storage rings – the cryogenic ring DESIREE with a circumference of 8.6 meters in Stockholm and the much smaller room temperature ring Mini-Ring in Lyon, which has a circumference of 0.71 meters. The RF rates were measured to be as high as 150 to 1000 s−1 for internal energies in the 7 to 9.4 eV energy range, where we have probed the time evolution of the internal energy distribution with nanosecond laser pulses with a 1 kHz repetition rate. These RF rates are found to be significantly higher than those of previously investigated smaller PAHs such as e.g. anthracene and naphthalene, for which the lowest non-forbidden electronic excited state, the D2 state, is populated with a smaller probability by inverse internal conversion. Furthermore, the D2–D0 transition rate is smaller for these smaller molecules than for tetracene. The complementary features of the two storage rings allow for RF rate measurements in a broader internal energy range than has been possible before. The smaller sampling period of about 6 μs in Mini-Ring is ideal to study the cooling dynamics of the hotter ions that decay fast, whereas DESIREE with a sampling period of about 60 μs is better suited to study the colder ions that decay on longer timescales ranging up to hundreds of milliseconds. The excellent agreement between the two series of measurements in the region where they overlap demonstrates the complementarity of the two electrostatic ion-beam storage rings.

  • 46. Bertolino, Mattias
    et al.
    Carlström, Stefanos
    Peschel, Jasper
    Zapata, Felipe
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Dahlström, Jan Marcus
    Thomas-Reiche-Kuhn correction for truncated configuration-interaction spaces: Case of laser-assisted dynamical interference2022In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 106, no 4, article id 043108Article in journal (Refereed)
    Abstract [en]

    The Thomas-Reiche-Kuhn sum rule is used to form an effective potential that is added to the time-dependent configuration-interaction singles (TDCIS) equations of motion in velocity gauge. The purpose of the effective potential is to include virtual coupling from singles to doubles, which is required for size-consistent velocity-gauge TDCIS results. The proposed method is compared to length-gauge TDCIS results for laser-assisted photoionization. Finally, a dynamical interference effect controlled by two-color fields is predicted for atomic targets. 

  • 47. Björck, M.
    et al.
    Soroka, I. L.
    Stockholm University, Faculty of Science, Department of Physics. Uppsala University, Sweden.
    Chacon-Carillo, C.
    Andersson, G.
    The asymmetric interface structure of bcc Fe82Ni18/Co superlattices as revealed by neutron diffraction2007In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 515, no 08-jul, p. 3619-3623Article in journal (Refereed)
    Abstract [en]

    The interface structure of Fe82Ni18/Co (001) Superlattices has been studied with a combination of X-ray and neutron diffraction. The analysis 'reveals highly asymmetric interfaces with total interface widths of 10 +/- 1 ML(monolayers) for Fe82Ni18 on Co and a maximum interface width of 1 ML for Co on Fe82Ni18. In addition it is concluded that there is no detectable long range B2-type chemical order occurring in the interface region. These results are also discussed in the context of previously measured magnetic mornents of the same system.

  • 48.
    Blanco, Carlos
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Princeton University, USA.
    Harris, Ian
    Kahn, Yonatan
    Lillard, Benjamin
    Pérez-Ríos, Jesús
    Molecular Migdal effect2022In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 106, no 11, article id 115015Article in journal (Refereed)
    Abstract [en]

    Nuclear scattering events with large momentum transfer in atomic, molecular, or solid-state systems may result in electronic excitations. In the context of atomic scattering by dark matter (DM), this is known as the Migdal effect, but the same effect has also been studied in molecules in the chemistry and neutron scattering literature. Here we present two distinct Migdal-like effects from DM scattering in molecules, which we collectively refer to as the molecular Migdal effect: a center-of-mass recoil, equivalent to the standard Migdal treatment; and a nonadiabatic coupling resulting from corrections to the Born-Oppenheimer approximation. The molecular bonds break spherical symmetry, leading to large daily modulation in the Migdal rate from anisotropies in the matrix elements. Our treatment reduces to the standard Migdal effect in atomic systems but does not rely on the impulse approximation or any semiclassical treatments of nuclear motion and as such may be extended to models where DM scatters through a long-range force. We demonstrate all of these features in a few simple toy models of diatomic molecules, namely, H+2, N2, and CO, and find total molecular Migdal rates competitive with those in semiconductors for the same target mass. We discuss how our results may be extended to more realistic targets comprised of larger molecules which could be deployed at the kilogram scale.

  • 49.
    Blomberg, Margareta
    Stockholm University.
    Reactions, bonding and spectra of organometallic and diatomic molecules, studied by high accuracy quantum chemical methods1983Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The main topic of the thesis is reductive elimination and oxidative addition reactions with nickel and palladium complexes. It is found that hydrogen is added to nickel much easier than both ethane and methane. This result can be understood from the reaction mechanisms; the spherical symmetry of the hydrogen atoms makes it easier for them than for methyl groups to bind in several directions simultanously, leading to lower barriers for reactions involving only hydrogen. Differences in the atomic spectra of nickel and palladium leads to differences in the reactions with hydrogen and it is found that the hydrogen bond is not as easily split by palladium as by nickel.

    Very accurate ground state potential curves are computed for Be2, F2 And NiH. For NiH also a large part of the electronic spectrum is calculated. Good agreement is obtained for those parameters that are experimentally known. In the spectrum of NiH, however, only one excited 2Δ band is found at 15000 cm-1, contrary to the earlier assignment of the experimentally obtained spectrum.

    Some other topics are also studied: predissociation in CC1, ligand rotation in nickel-bis-dithiolene, the point dipole approximation in the Solomon-Bloembergen equation and the electronic structure of beryllium and lithium complexes.

    The methods used are in most cases multiconfiguration SCF and large scale configuration interaction calculations.

  • 50.
    Blomberg, Mattias
    Stockholm University, Faculty of Science, Department of Physics.
    Redox Reactions of NO and O2 in Iron Enzymes: A Density Functional Theory Study2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In the present thesis the density functional B3LYP has been used to study reactions of NO and O2 in redox active enzymes.

    Reduction of nitric oxide (NO) to nitrous oxide (N2O) is an important part in the bacterial energy conservation (denitrification). The reduction of NO in three different bimetallic active sites leads to the formation of hyponitrous acid anhydride (N2O22-). The stability of this intermediate is crucial for the reaction rate. In the two diiron systems, respiratory and scavenging types of NOR, it is possible to cleave the N-O bond, forming N2O, without any extra protons or electrons. In a heme-copper oxidase, on the other hand, both a proton and an electron are needed to form N2O.

    In addition to being an intermediate in the denitrification, NO is a toxic agent. Myoglobin in the oxy-form reacts with NO forming nitrate (NO3 -) at a high rate, which should make this enzyme an efficient NO scavenger. Peroxynitrite (ONOO-) is formed as a short-lived intermediate and isomerizes to nitrate through a radical reaction.

    In the mechanism for pumping protons in cytochrome oxidase, thermodynamics, rather than structural changes, might guide protons to the heme propionate for further translocation.

    The dioxygenation of arachidonic acid in prostaglandin endoperoxide H synthase forms the bicyclic prostaglandin G2, through a cascade of radical reactions. The mechanism proposed by Hamberg and Samuelsson is energetically feasible.

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