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  • 1. Andersson, E.
    et al.
    Fritzsche, S.
    Linusson, Per
    Stockholm University, Faculty of Science, Department of Physics.
    Hedin, L.
    Eland, J. H. D.
    Rubensson, J. -E
    Karlsson, L.
    Feifel, R.
    Multielectron coincidence study of the double Auger decay of 3d-ionized krypton2010In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 82, no 4, 043418- p.Article in journal (Refereed)
    Abstract [en]

    Multielectron coincidence data for triple ionization of krypton have been recorded above the 3d ionization threshold at two photon energies (140 and 150 eV). Three principal transition pathways have been observed, two involving double Auger transitions from Kr+, and one involving single Auger transitions from Kr2+ created by direct single-photon double ionization. The decay of the 3d(9) D-2(5/2,3/2) states in Kr+ has been analyzed in some detail and is found to be strongly dominated by cascade processes where two electrons with well-defined energies are emitted. The decay paths leading to the 4s(2)4p(3) S-4, D-2, and P-2 states of Kr3+ are analyzed and energies of seven intermediate states in Kr2+ are given. A preliminary investigation of the decay paths from Kr+ 3d (9)4p(5)nl shake-up states has also been carried out.

  • 2. Andersson, E.
    et al.
    Linusson, Per
    Stockholm University, Faculty of Science, Department of Physics.
    Fritzsche, S.
    Hedin, L.
    Eland, J. H. D.
    Karlsson, L.
    Rubensson, J. -E
    Feifel, R.
    Formation of Kr3+ via core-valence doubly ionized intermediate states2012In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 85, no 3, 032502- p.Article in journal (Refereed)
    Abstract [en]

    The time-of-flight photoelectron-photoion coincidence technique has been used to study single-photon 3d(9)4p(5) core-valence double ionization of Kr and subsequent Auger decay to triply charged states associated with the 4s(2)4p(3) and 4s(1)4p(4) configurations. The photon energy used was h nu = 150 eV. Multiconfiguration Dirac-Fock calculations were performed both for the doubly ionized intermediate states and the triply ionized final states. The intermediate states of Kr2+ are observed between 120 and 125 eV, whereas the final states of Kr3+ are observed between 74- and 120-eV ionization energy. Assignments of all structures are made based on the present numerical results. The calculated Auger rates give a detailed explanation of the relative line strengths observed.

  • 3. Andersson, J.
    et al.
    Beerwerth, R.
    Linusson, Per
    Stockholm University, Faculty of Science, Department of Physics.
    Eland, J. H. D.
    Zhaunerchyk, V.
    Fritzsche, S.
    Feifel, R.
    Triple ionization of atomic Cd involving 4p(-1) and 4s(-1) inner-shell holes2015In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 92, no 2, 023414Article in journal (Refereed)
    Abstract [en]

    The triple ionization spectrum of atomic Cd formed upon the removal of a 4p or a 4s inner-shell electron and subsequent Auger decays has been obtained at 200 eV photon energy. By using a versatile multielectron coincidence detection technique based on a magnetic bottle spectrometer in combination with multiconfiguration Dirac-Fock calculations, Auger cascades leading to tricationic final states have been analyzed and final-state configurations have been identified. The most prominent Auger cascades leading to the ground state of Cd3+ have been identified in good agreement with theory.

  • 4. Aolita, Leandro
    et al.
    Gallego, Rodrigo
    Acin, Antonio
    Chiuri, Andrea
    Vallone, Giuseppe
    Mataloni, Paolo
    Cabello, Adan
    Stockholm University, Faculty of Science, Department of Physics.
    Fully nonlocal quantum correlations2012In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 85, no 3, 032107- p.Article in journal (Refereed)
    Abstract [en]

    Quantum mechanics is a nonlocal theory, but not as nonlocal as the no-signalling principle allows. However, there exist quantum correlations that exhibit maximal nonlocality: they are as nonlocal as any nonsignalling correlation and thus have a local content, quantified by the fraction p(L) of events admitting a local description, equal to zero. We exploit the known link between the Kochen-Specker and Bell theorems to derive a maximal violation of a Bell inequality from every Kochen-Specker proof. We then show that these Bell inequalities lead to experimental bounds on the local content of quantum correlations that are significantly better than those based on other constructions. We perform the experimental demonstration of a Bell test originating from the Peres-Mermin Kochen-Specker proof, providing an upper bound on the local content pL less than or similar to 0.22.

  • 5. 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, 030101- p.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.

  • 6. 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, 053405- p.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.

  • 7. Asboth, Janos K.
    et al.
    Edge, Jonathan M.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Edge-state-enhanced transport in a two-dimensional quantum walk2015In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 91, no 2, 022324Article in journal (Refereed)
    Abstract [en]

    Quantum walks on translation-invariant regular graphs spread quadratically faster than their classical counterparts. The same coherence that gives them this quantum speedup inhibits or even stops their spread in the presence of disorder. We ask how to create an efficient transport channel from a fixed source site (A) to fixed target site (B) in a disordered two-dimensional discrete-time quantum walk by cutting some of the links. We show that the somewhat counterintuitive strategy of cutting links along a single line connecting A to B creates such a channel. The efficient transport along the cut is due to topologically protected chiral edge states, which exist even though the bulk Chern number in this system vanishes. We give a realization of the walk as a periodically driven lattice Hamiltonian and identify the bulk topological invariant responsible for the edge states as the quasienergy winding of this Hamiltonian.

  • 8.
    Badziag, Piotr
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Horodecki, Karol
    Horodecki, Michal
    Jenkinson, Justin
    Szarek, Stanislaw J.
    Bound entangled states with extremal properties2014In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 90, no 1, 012301- p.Article in journal (Refereed)
    Abstract [en]

    Following recent work of Beigi and Shor, we investigate positive partial transpose (PPT) states that are heavily entangled. We first exploit volumetric methods to show that in a randomly chosen direction, there are PPT states whose distance in trace norm from separable states is (asymptotically) at least 1/4. We then provide explicit examples of PPT states which are nearly as far from separable ones as possible. To obtain a distance of 2 - c from the separable states, we need a dimension of 2(poly[log(1/epsilon)]), as opposed to 2(poly(1/epsilon)) given by the construction of Beigi and Shor [J. Math. Phys. 51, 042202 (2010)]. We do so by exploiting the so-called private states, introduced earlier in the context of quantum cryptography. We also provide a lower bound for the distance between private states and PPT states and investigate the distance between pure states and the set of PPT states.

  • 9.
    Badziag, Piotr
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Horodecki, Pawel
    Horodecki, Ryszard
    Augusiak, Remigiusz
    Separability in terms of a single entanglement witness2013In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 88, no 1, 010301- p.Article in journal (Refereed)
    Abstract [en]

    The separability problem is formulated in terms of a characterization of a single entanglement witness. More specifically, we show that any (in general multipartite) state rho is separable if and only if a specially constructed entanglement witness W-rho is weakly optimal, i.e., its expectation value vanishes on at least one product vector. Interestingly, the witness can always be chosen to be decomposable. Our result changes the conceptual aspect of the separability problem and raises some questions about the properties of positive maps.

  • 10.
    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, 013415- p.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.

  • 11. Bahati, E. M.
    et al.
    Fogle, M.
    Vane, C. R.
    Bannister, M. E.
    Thomas, R. D.
    Stockholm University, Faculty of Science, Department of Physics.
    Zhaunerchyk, Vitali
    Stockholm University, Faculty of Science, Department of Physics.
    Electron-impact dissociation of CD3+ and CH3+ ions producing CD2+, CH+ and C+ fragment ions2009In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 79, no 5, 52703- p.Article in journal (Refereed)
    Abstract [en]

    Using a crossed electron-ion beams method, we measured absolute cross sections for electron-impact dissociation of the CD3+ molecular ions producing CD2+ fragment ions and CH3+ ions yielding CH+ and C+ fragment ions over a collision energy range from a few eV up to 100 eV. The total experimental uncertainties are about 12% at the maximum of the curves of cross sections (peak of the cross section for the CH+ channel). The obtained results suggest important roles played by predissociation of bound states in the production of both the CH+ and C+ fragment ions. Good agreement is found with other results reported for the CH+ fragment, but some differences are found for the CD2+ and C+ fragments.

  • 12. Barillot, T.
    et al.
    Cauchy, C.
    Hervieux, P. -A
    Gisselbrecht, M.
    Canton, S. E.
    Johnsson, P.
    Laksman, J.
    Mansson, E. P.
    Dahlström, J. Marcus
    Stockholm University, Faculty of Science, Department of Physics.
    Magrakvelidze, M.
    Dixit, G.
    Madjet, M. E.
    Chakraborty, H. S.
    Suraud, E.
    Dinh, P. M.
    Wopperer, P.
    Hansen, K.
    Loriot, V.
    Bordas, C.
    Sörensen, S.
    Lepine, F.
    Angular asymmetry and attosecond time delay from the giant plasmon resonance in C-60 photoionization2015In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 91, no 3, 033413Article in journal (Refereed)
    Abstract [en]

    This combined experimental and theoretical study demonstrates that the surface plasmon resonance in C-60 alters the valence photoemission quantum phase, resulting in strong effects in the photoelectron angular distribution and emission time delay. Electron momentum imaging spectroscopy is used to measure the photoelectron angular distribution asymmetry parameter that agrees well with our calculations from the time-dependent local density approximation (TDLDA). Significant structure in the valence photoemission time delay is simultaneously calculated by TDLDA over the plasmon active energies. Results reveal a unified spatial and temporal asymmetry pattern driven by the plasmon resonance and offer a sensitive probe of electron correlation. A semiclassical approach facilitates further insights into this link that can be generalized and applied to other molecular systems and nanometer-sized metallic materials exhibiting plasmon resonances.

  • 13.
    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, 043631- p.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.

  • 14. Baym, Gordon
    et al.
    Pethick, Christopher J.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Landau critical velocity in weakly interacting Bose gases2012In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 86, no 2, 023602- p.Article in journal (Refereed)
    Abstract [en]

    The flow of a uniform Bose gas at speeds greater than the Landau critical velocity nu(c) does not necessarily destroy superfluidity, but rather needs only to lead to a decrease of the superfluid mass density rho(s). Analyzing a weakly interacting Bose gas with a finite-range interparticle interaction that leads to a Landau critical velocity at nonzero quasiparticle momentum, we explicitly construct the (nonuniform) condensate for fluid flow faster than nu(c) and calculate the accompanying decrease in rho s. We briefly comment on the relation of the physics to other problems in superfluids, e.g., solitons and vortices in Bose-Einstein condensates, and critical currents in superconductors.

  • 15.
    Bengtsson, Ingemar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Kus, Marek
    'Classical' Quantum States2009In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 80, no 2, 022319- p.Article in journal (Refereed)
    Abstract [en]

    We show that several classes of mixed quantum states in finite-dimensional Hilbert spaces which can be characterized as being, in some respect, "most classical" can be described and analyzed in a unified way. Among the states we consider are separable states of distinguishable particles, uncorrelated states of indistinguishable fermions and bosons, as well as mixed spin states decomposable into probabilistic mixtures of pure coherent states. The latter was the subject of the recent paper by Giraud et al. [Phys. Rev. A 78, 042112 (2008)], who showed that in the lowest-dimensional nontrivial case of spin 1, each such state can be decomposed into a mixture of eight pure states. Using our method, we prove that in fact four pure states always suffice.

  • 16.
    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, 053413- p.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.

  • 17.
    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, 032502- p.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.

  • 18.
    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, 013419- p.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.

  • 19.
    Bogdanski, Jan
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Rafiei, Nima
    Bourennane, Mohamed
    Stockholm University, Faculty of Science, Department of Physics.
    Experimental quantum secret sharing using telecommunication fiber2008In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 78, no 6Article in journal (Refereed)
    Abstract

    We report quantum secret sharing experiment in telecommunication fiber in five-party implementation. The quantum secret sharing experiment has been based on a single qubit protocol, which has opened the door to practical secret sharing implementation over fiber channels and in free space. The previous quantum secret sharing proposals were based on multiparticle entangled states, difficult in the practical implementation and not scalable. The secret sharing protocol has been implemented in an interferometric fiber optics setup with phase encoding and demonstrated for three, four, and five parties. The experimental setup measurements have shown feasibility and scalability of secure multiparty quantum communication over commercial telecom fiber networks.

  • 20.
    Brinne Roos, Johanna
    et al.
    Department of Theoretical Chemistry, School of Biotechnology, Royal Institute of Technology, Stockholm.
    Larson, Åsa
    Department of Theoretical Chemistry, School of Biotechnology, Royal Institute of Technology, Stockholm.
    Orel, Ann
    Department of Applied Science, University of California, Davis.
    Electron collisions with H3+: Ion-pair formation2007In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 76, no 4, 042703-1-042703-9 p.Article in journal (Refereed)
    Abstract [en]

    The formation of the ion pair H2++H in electron recombination with H3+ is studied. The diabatic potentials and electronic couplings are extracted from ab initio electron scattering calculations as well as quantum chemistry calculations. In order to describe this reaction we include six coupled electronic states and propagate wave packets in two dimensions using the multiconfiguration time-dependent Hartree method. Also, the cross section for ion-pair formation in electron recombination with D3+ is calculated. The cross section for this isotopomer is found to be about a factor of 3 smaller than the cross section for H3+.

  • 21.
    Brinne Roos, Johanna
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Orel, Ann E.
    Dept of Applied Science US Davis.
    Dissociative recombination of HF+2008In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 78, no 2, 022508-1-022508-12 p.Article in journal (Refereed)
    Abstract [en]

    The direct mechanism of dissociative recombination of HF+ is studied usingboth time-dependent and time-independent methods, where the dynamics on 30resonant states is explored. The relevant electronic states are calculatedab initio by combining electron scattering calculations with multireference configurationinteraction structure calculations. For collision energies between 0.04 and 10  eV,we obtain qualitative agreement with experiment. At 1.9  eV there isa sharp threshold in both the experimental and theoretical crosssections that can be explained by the opening of newasymptotic limits. The measured cross section below 0.04  eV is notreproduced due to the neglect of the electronic couplings betweenthe neutral states. We examine the validity of the localapproximation for treating autoionization from the resonant states included inthis study.

  • 22.
    Cabello, Adan
    et al.
    Stockholm University, Faculty of Science, Department of Physics. University of Sevilla, Spain.
    Amselem, Elias
    Stockholm University, Faculty of Science, Department of Physics.
    Blanchfield, Kate
    Stockholm University, Faculty of Science, Department of Physics.
    Bourennane, Mohamed
    Stockholm University, Faculty of Science, Department of Physics.
    Bengtsson, Ingemar
    Stockholm University, Faculty of Science, Department of Physics.
    Proposed experiments of qutrit state-independent contextuality and two-qutrit contextuality-based nonlocality2012In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 85, no 3, 032108- p.Article in journal (Refereed)
    Abstract [en]

    Recent experiments have demonstrated ququart state-independent quantum contextuality and qutrit state-dependent quantum contextuality. So far, the most basic form of quantum contextuality pointed out by Kochen and Specker, and Bell, has eluded experimental confirmation. Here we present an experimentally feasible test to observe qutrit state-independent quantum contextuality using single photons in a three-path setup. In addition, we show that if the same measurements are performed on two entangled qutrits, rather than sequentially on the same qutrit, then the noncontextual inequality becomes a Bell inequality. We show that this connection also applies to other recently introduced noncontextual inequalities.

  • 23.
    Cabello, Adan
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    D'Ambrosio, Vincenzo
    Nagali, Eleonora
    Sciarrino, Fabio
    Hybrid ququart-encoded quantum cryptography protected by Kochen-Specker contextuality2011In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 84, no 3, 030302- p.Article in journal (Refereed)
    Abstract [en]

    Quantum cryptographic protocols based on complementarity are not secure against attacks in which complementarity is imitated with classical resources. The Kochen-Specker (KS) theorem provides protection against these attacks, without requiring entanglement or spatially separated composite systems. We analyze the maximum tolerated noise to guarantee the security of a KS-protected cryptographic scheme against these attacks and describe a photonic realization of this scheme using hybrid ququarts defined by the polarization and orbital angular momentum of single photons.

  • 24.
    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, 023420- p.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

  • 25.
    Carette, Thomas
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Nemouchi, Messaoud
    Li, Jiguang
    Godefroid, Michel
    Relativistic effects on the hyperfine structures of 2 p(4)(P-3)3 p D-2(o), D-4(o), and P-4(o) in F-19 I2013In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 88, no 4, 042501- p.Article in journal (Refereed)
    Abstract [en]

    The hyperfine interaction constants of the 2p(4)(P-3)3p D-2(3/2,5/2)o, D-4(1/2-7/2)o, and P-4(1/2-5/2)o levels in neutral fluorine are investigated theoretically. Large-scale calculations are carried out using the multiconfiguration Hartree-Fock (MCHF) and Dirac-Hartree-Fock (MCDHF) methods. In the framework of the MCHF approach, the relativistic effects are taken into account in the Breit-Pauli approximation using nonrelativistic orbitals. In the fully relativistic approach, the orbitals are optimized using the Dirac-Coulomb Hamiltonian with correlation models inspired by the nonrelativistic calculations. Higher-order excitations are captured through multireference configuration interaction calculations including the Breit interaction. In a third (intermediate) approach, the Dirac-Coulomb-Breit Hamiltonian matrix is diagonalized in a relativistic configuration space built with nonrelativistic MCHF radial functions converted into Dirac spinors using the Pauli approximation. The magnetic dipole hyperfine-structure constants calculated with the three relativistic models are consistent and reveal unexpectedly large effects of relativity for 2D(5/2)(o), P-4(3/2)o, and P-4(5/2)o. The agreement with the few available experimental values is satisfactory. The strong J dependence of relativistic corrections on the hyperfine constants is investigated through the detailed analysis of the orbital, spin-dipole, and contact relative contributions calculated with the nonrelativistic magnetic dipole operator.

  • 26. Chen, Jing-Ling
    et al.
    Su, Hong-Yi
    Wu, Chunfeng
    Deng, Dong-Ling
    Cabello, Adan
    Stockholm University, Faculty of Science, Department of Physics.
    Kwek, L. C.
    Oh, C. H.
    Quantum contextuality for a relativistic spin-1/2 particle2013In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 87, no 2, 022109- p.Article in journal (Refereed)
    Abstract [en]

    The quantum predictions for a single nonrelativistic spin-1/2 particle can be reproduced by noncontextual hidden variables. Here we show that quantum contextuality for a relativistic electron moving in a Coulomb potential naturally emerges if relativistic effects are taken into account. The contextuality can be identified through the violation of noncontextuality inequalities. We also discuss quantum contextuality for the free Dirac electron as well as the relativistic Dirac oscillator. DOI: 10.1103/PhysRevA.87.022109

  • 27. Chourou, S. T.
    et al.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Orel, A. E.
    Low-energy dissociative electron attachment to CF22015In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 92, no 2, 022702Article in journal (Refereed)
    Abstract [en]

    We present the results of a theoretical study of dissociative electron attachment (DEA) of low-energy electrons to CF2. We carried out electron scattering calculations using the complex Kohn variational method at the static-exchange and relaxed self-consistent field (SCF) level at the equilibrium geometry and compare our differential cross sections to other results. We then repeated these calculations as a function of the three internal degrees of freedom to obtain the resonance energy surfaces and autoionization widths. We use this data as input to form the Hamiltonian relevant to the nuclear dynamics. The multidimensional wave equation is solved using the multiconfiguration time-dependent Hartree (MCTDH) approach within the local approximation.

  • 28. Ciappina, M. F.
    et al.
    Schulz, M.
    Kirchner, T.
    Fischer, D
    Stockholm University.
    Moshammer, R.
    Ullrich, J.
    Double ionization of helium by ion impact analyzed using four-body Dalitz plots2008In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 77, no 6, 62706- p.Article in journal (Refereed)
    Abstract [en]

    We have performed experimental and theoretical studies of double ionization of helium by 6 MeV proton impact using a recently developed tool, four-particle Dalitz plots [Schulz , J. Phys. B 22, 3091 (2007)] which enable the representation of multiple differential cross sections as a function of all four fragments in a single spectrum without loss of any part of the total cross section. As a result, the relative importance of the various interactions between the fragments can be studied in great detail. Comparisons of experimental data with theoretical first-order calculations and simulations for the higher-order (TS-2) process show that elastic scattering between the heavy particles is surprisingly strong. For a large fraction of collision events, the final-state electron momenta are small compared to the momenta of the heavy particles. Our results suggest that an uncorrelated double ionization mechanism, involving two independent interactions of the projectile with both electrons, is significantly more important than previously expected for such fast collisions.

  • 29. da Silva, Humberto, Jr.
    et al.
    Oller, Javier
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Hervieux, Paul-Antoine
    Adoui, Lamri
    Alcami, Manuel
    Huber, Bernd A.
    Martin, Fernando
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Rousseau, Patrick
    Diaz-Tendero, Sergio
    Multiple electron capture, excitation, and fragmentation in C6+-C-60 collisions2014In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 90, no 3, 032701- p.Article in journal (Refereed)
    Abstract [en]

    We present experimental and theoretical results on single- and multiple-electron capture, and fragmentation, in C6+ + C-60 collisions at velocities in the v(col) = 0.05 - 0.4 a.u. range. We use time-of-flight mass spectrometry and coincidence detection of charged fragments to separate pure target ionization from processes in which the C-60 target is both ionized and fragmented. The coincidence technique allows us to identify different types of fragmentation processes such as C-60(q+) -> C-58(q+) + C-2 and C-60(q+) -> C-58((q-1)+) + C-2(+). A quasimolecular approach is employed to calculate charge transfer and target excitation cross sections. First-order time-dependent perturbation and statistical methods are used to treat the postcollisional processes: the calculated rate constants for C-2 and C-2(+) emission from the excited and charged fullerene are then used to evaluate the fragmentation dynamics. We show that the target ionization cross section decreases with the induced target charge state and the impact energy. C-2 emission from C-60(q+) is found to dominate when q <= 2 while C-2(+) emission dominates when q >= 5, in agreement with the present and previous experimental results.

  • 30.
    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, 061402- p.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

  • 31. Deuretzbacher, F.
    et al.
    Bruun, G. M.
    Pethick, Christopher
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). KTH Royal Inst Technol, NORDITA, SE-10691 Stockholm, Sweden.
    Jona-Lasinio, M.
    Reimann, S. M.
    Santos, L.
    Self-bound many-body states of quasi-one-dimensional dipolar Fermi gases: Exploiting Bose-Fermi mappings for generalized contact interactions2013In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 88, no 3, 033611- p.Article in journal (Refereed)
    Abstract [en]

    Using a combination of results from exact mappings and from mean-field theory we explore the phase diagram of quasi-one-dimensional systems of identical fermions with attractive dipolar interactions. We demonstrate that at low density these systems provide a realization of a single-component one-dimensional Fermi gas with a generalized contact interaction. Using an exact duality between one-dimensional Fermi and Bose gases, we show that when the dipole moment is strong enough, bound many-body states exist, and we calculate the critical coupling strength for the emergence of these states. At higher densities, the Hartree-Fock approximation is accurate, and by combining the two approaches we determine the structure of the phase diagram. The many-body bound states should be accessible in future experiments with ultracold polar molecules.

  • 32. Dolfi, Michele
    et al.
    Kantian, Adrian
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Bauer, Bela
    Troyer, Matthias
    Minimizing nonadiabaticities in optical-lattice loading2015In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 91, no 3, 033407Article in journal (Refereed)
    Abstract [en]

    In the quest to reach lower temperatures of ultracold gases in optical-lattice experiments, nonadiabaticities during lattice loading represent one of the limiting factors that prevent the same low temperatures being reached as in experiments without lattices. Simulating the loading of a bosonic quantum gas into a one-dimensional optical lattice with and without a trap, we find that the redistribution of atomic density inside a global confining potential is by far the dominant source of heating. Based on these results we propose adjusting the trapping potential during loading to minimize changes to the density distribution. Our simulations confirm that a very simple linear interpolation of the trapping potential during loading already significantly decreases the heating of a quantum gas, and we discuss how loading protocols minimizing density redistributions can be designed.

  • 33. Eland, J. H. D.
    et al.
    Linusson, Per
    Stockholm University, Faculty of Science, Department of Physics.
    Hedin, L.
    Andersson, E.
    Rubensson, J. -E
    Feifel, R.
    Coincidence technique using synchrotron radiation for triple photoionization: Results on rare gas atoms2008In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 78, no 6, 63423- p.Article in journal (Refereed)
    Abstract [en]

    Final-state trication spectra and electron distributions produced by soft x-ray single-photon triple ionization of rare gas atoms have been obtained by a multiple-coincidence technique using storage-ring synchrotron radiation. The technique uses electron time of flight with ion detection to overcome the problem of high repetition rates in single-bunch operation. A correction needed to the triple-ionization energy of Kr currently listed in standard tables is confirmed, and the method's ability to examine the three-electron distributions, characterizing the ionization mechanisms and post-collision interactions, is illustrated.

  • 34. Ferger, T.
    et al.
    Schulz, M.
    Fischer, D.
    Stockholm University.
    Najjari, B.
    Moshammer, R.
    Ullrich, J.
    Triple-differential cross sections for target ionization with simultaneous projectile detachment in 200-keV H-+He collisions2007In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 76, no 4, 42708- p.Article in journal (Refereed)
    Abstract [en]

    We have performed a kinematically complete experiment for target ionization with simultaneous projectile detachment (TIPD) in 200-keV H-+He collisions. From the data we extracted triple-differential cross sections (TDCSs) for each electron separately. These TDCSs closely resemble corresponding data for single ionization by charged-particle impact. Surprisingly, the contributions from higher-order processes to TIPD, proceeding through two independent interactions of each electron with the core of the respective other collision partner, are found to be somewhat larger than the first-order process proceeding through the electron-electron interaction.

  • 35. Fernandez-Vidal, Sonia
    et al.
    De Chiara, Gabriele
    Larson, Jonas
    Stockholm University, Faculty of Science, Department of Physics.
    Morigi, Giovanna
    Quantum ground state of self-organized atomic crystals in optical resonators2010In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 81, no 4, 43407- p.Article in journal (Refereed)
    Abstract [en]

    Cold atoms, driven by a laser and simultaneously coupled to the quantum field of an optical resonator, may self-organize in periodic structures. These structures are supported by the optical lattice, which emerges from the laser light they scatter into the cavity mode and form when the laser intensity exceeds a threshold value. We study theoretically the quantum ground state of these structures above the pump threshold of self-organization by mapping the atomic dynamics of the self-organized crystal to a Bose-Hubbard model. We find that the quantum ground state of the self-organized structure can be the one of a Mott insulator, depending on the pump strength of the driving laser. For very large pump strengths, where the intracavity-field intensity is maximum and one would expect a Mott-insulator state, we find intervals of parameters where the phase is compressible. These states could be realized in existing experimental setups.

  • 36.
    Fischer, D.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Gudmundsson, Magnus
    Stockholm University, Faculty of Science, Department of Physics.
    Berenyi, Zoltan
    Stockholm University, Faculty of Science, Department of Physics.
    Haag, Nicole
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, Henrik A. B.
    Stockholm University, Faculty of Science, Department of Physics.
    Misra, Deepankar
    Stockholm University, Faculty of Science, Department of Physics.
    Reinhed, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Kallberg, A.
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Simonsson, Ansgar
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Stochkel, K.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, H. T.
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Importance of Thomas single-electron transfer in fast p-He collisions2010In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 81, no 1, 12714- p.Article in journal (Refereed)
    Abstract [en]

    We report experimental angular differential cross sections for nonradiative single-electron capture in p-He collisions (p + He -> H + He+) with a separate peak at the 0.47 mrad Thomas scattering angle for energies in the 1.3-12.5 MeV range. We find that the intensity of this peak scales with the projectile velocity as v(P)(-11). This constitutes the first experimental test of the prediction from 1927 by L. H. Thomas [Proc. R. Soc. 114, 561 (1927)]. At our highest energy, the peak at the Thomas angle contributes with 13.5% to the total integrated nonradiative single-electron capture cross section.

  • 37. Fogle, M.
    et al.
    Bahati, E. M.
    Bannister, M. E.
    Deng, S. H. M.
    Vane, C. R.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Zhaunerchyk, Vitali
    Stockholm University, Faculty of Science, Department of Physics.
    Electron-impact dissociation of XH2+ (X = B, C, N, O, F): Absolute cross sections for production of XH+ and X+ fragment ions2010In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 82, no 4, 042720- p.Article in journal (Refereed)
    Abstract [en]

    Absolute cross sections for electron-impact dissociation of XH2+ (X = B, C, N, O, F) producing XH+ and X+ ion fragments were measured in the 3- to 100-eV range using a crossed-electron-ion beams technique. Dissociative excitation of BD2+ and CH2+ producing B+ and C+, respectively, show a propensity toward a two-body dissociation while the remaining species all tend to show a three-body dissociation dynamic. The BD+ and CH+ dissociative excitation channels show a large resonant-type contribution to the cross sections at similar to 10eV. For the X+ fragment ion production cross sections, a clear dependence on the threshold energy, as it relates to the rate of rise in the cross section above threshold, is observed.

  • 38. Fogle, M.
    et al.
    Bahati, E. M.
    Bannister, M. E.
    Deng, S. H. M.
    Vane, C. R.
    Thomas, Richard D.
    Zhaunerchyk, Vitali
    Stockholm University, Faculty of Science, Department of Physics.
    Electron-impact dissociative excitation and ionization of N(2)D(+)2011In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 84, no 3, 032714- p.Article in journal (Refereed)
    Abstract [en]

    Absolute cross sections for electron-impact dissociation of N(2)D(+) producing N(2)(+), ND(+), and N(+) ion fragments were measured in the 5- to 100-eV range using a crossed electron-ion beams technique. In the 5- to 20-eV region, in which dissociative excitation (DE) is the principal contributing mechanism, N(2)(+) production dominates. The N(2)(+) + D dissociation channel shows a large resonant-like structure in the DE cross section, as observed previously in electron impact dissociation of triatomic dihydride species [M. Fogle, E. M. Bahati, M. E. Bannister, S. H. M. Deng, C. R. Vane, R. D. Thomas, and V. Zhaunerchyk, Phys. Rev. A 82, 042720 (2010)]. In the dissociative ionization (DI) region, 20- to 100-eV, N(2)(+), ND(+), and N(+) ion fragment production are comparable. The observance of the ND(+) and N(+) ion fragments indicate breaking of the N-N bond along certain dissociation channels.

  • 39.
    Gatchell, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Rousseau, P.
    Domaracka, A.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Chen, Tao
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Chesnel, J. Y.
    Mery, A.
    Maclot, S.
    Adoui, L.
    Huber, B. A.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Ions colliding with mixed clusters of C-60 and coronene: Fragmentation and bond formation2014In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 90, no 2, 022713Article in journal (Refereed)
    Abstract [en]

    We have studied collisions between 22.5 keV He2+ ions and mixed clusters [(C-60)(m)(C24H12)(n)] of m C-60 and n coronene molecules where m and n range up to about ten. Surprisingly, the cluster fragmentation behavior in distant collisions is dramatically different for pure coronene clusters (m = 0) and clusters containing a single C-60 molecule (m = 1). In the latter case, the clusters may be ionized without also being fragmented on the experimental time scale of tens of microseconds. This does not occur for pure coronene clusters, but is a main characteristic of pure fullerene clusters. For ion trajectories penetrating the mixed cluster, we observe covalent bond formations between C-59 or C-58 and C-60, but not between coronene fragments and C-60, or between C-60 fragments and coronene. These results are explained by means of classical molecular dynamics simulations of collisions inside the fragmenting mixed clusters.

  • 40.
    Gatchell, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics. Aarhus University, Denmark.
    de Ruette, Nathalie
    Stockholm University, Faculty of Science, Department of Physics.
    Chen, Tao
    Stockholm University, Faculty of Science, Department of Physics.
    Giacomozzi, Linda
    Stockholm University, Faculty of Science, Department of Physics.
    Nascimento, Rodrigo F.
    Stockholm University, Faculty of Science, Department of Physics.
    Wolf, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Anderson, Emma K.
    Stockholm University, Faculty of Science, Department of Physics.
    Delaunay, R.
    Vizcaino, V.
    Rousseau, P.
    Adoui, L.
    Huber, B. A.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Failure of hydrogenation in protecting polycyclic aromatic hydrocarbons from fragmentation2015In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 92, no 5, 050702Article in journal (Refereed)
    Abstract [en]

    A recent study of soft x-ray absorption in native and hydrogenated coronene cations, C24H12+m + m = 0-7, led to the conclusion that additional hydrogen atoms protect (interstellar) polycyclic aromatic hydrocarbon (PAH) molecules from fragmentation [Reitsma et al., Phys. Rev. Lett. 113, 053002 (2014)]. The present experiment with collisions between fast (30-200 eV) He atoms and pyrene (C16H10+m +, m = 0, 6, and 16) and simulations without reference to the excitation method suggests the opposite. We find that the absolute carbon-backbone fragmentation cross section does not decrease but increases with the degree of hydrogenation for pyrene molecules.

  • 41.
    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, 052112- p.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.

  • 42. 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, 053424- p.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.

  • 43.
    Gurell, Jonas
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Biémont, E.
    Blagoev, K.
    Fivet, V.
    Lundin, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Mannervik, Sven
    Stockholm University, Faculty of Science, Department of Physics.
    Norlin, L-O
    Stockholm University, Faculty of Science, Department of Physics.
    Quinet, P.
    Rostohar, D.
    Royen, Peder
    Stockholm University, Faculty of Science, Department of Physics.
    Schef, P.
    Laser-probing measurements and calculations of lifetimes of the 5d 2D3/2 and 5d 2D5/2 metastable levels in Ba II2007In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 75, no 5, 052506- p.Article in journal (Refereed)
    Abstract [en]

    The two metastable levels 5d 2D3∕2 and 5d 2D5∕2 in Ba II both show extremely long lifetimes of the order of several tens of seconds each. This has been found both by experiments and by theoretical predictions. The small transition probabilities associated with these two levels make them interesting and challenging for theoreticians as well as for experimentalists. Several calculations and measurements of these two lifetimes have been made previously but discrepancies between the results are present. This article presents values of τ=89.4±15.6 s for the 2D3∕2 level and τ=32.0±4.6 s for the 2D5∕2 level measured in a beam-laser experiment performed at the ion storage ring CRYRING. These values are supported by our new calculations resulting in τ=82.0 s for the 2D3∕2 level and τ=31.6 s for the 2D5∕2 level.

  • 44. Gutierrez-Esparza, A. J.
    et al.
    Pimenta, W. M.
    Marques, B.
    Stockholm University, Faculty of Science, Department of Physics. Universidade Federal de Minas Gerais, Brazil.
    Matoso, A. A.
    Sperling, J.
    Vogel, W.
    Padua, S.
    Detection of nonlocal superpositions2014In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 90, no 3, 032328- p.Article in journal (Refereed)
    Abstract [en]

    We study in theory and experiment the verification of the Schmidt number of quantum correlated radiation fields. This measure of entanglement counts the number of global superpositions of product states which are needed to describe a compound quantum system. For unraveling a certain value of this measure, a family of entanglement and Schmidt number tests is constructed. The measurement of the whole class of witnesses is realized. By generating a path entangled two-photon state, we demonstrate the feasibility to directly count quantum superpositions.

  • 45. Hoshino, Masamitsu
    et al.
    Kambara, Tadashi
    Kanai, Yasuyuki
    Schuch, Reinhold
    Stockholm University, Faculty of Science, Department of Physics.
    Yamazaki, Yasunori
    Multielectron processes in close collisions of slow Neq+ (q=1-9) ions with Ar atoms2007In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 75, no 3, 32722- p.Article in journal (Refereed)
    Abstract [en]

    We have studied the multielectron processes in close collisions between slow Neq+ ions (q=1-9, energies of 5 and 14 keV) and Ar atoms through measurements of the charge-state correlations between 27 degrees scattered and 70 degrees recoiling ions. At the selected scattering angle, the internuclear distance of the closest approach at 35 keV is comparable to the L-shell radius of Ar atoms. A drastic difference between low-charged (q=1-3) and highly charged (q=7-9) Ne ions was found. For example, the most probable channel for the Ne7+ projectile is three-electron capture accompanied with two-electron loss whereas for the Ne+ projectile pure double ionization was found most probable. As a general trend, the mean charges of the both ions and the mean number of captured electrons increase almost linearly with incident charge q, while the mean number of ejected electrons from the system is independent of q at both 5 and 14 keV. We also measured the charge state distributions of the Ar recoil ions as function of the Neq+ (q=3, 5, and 7) energies between 5 and 63 keV, which corresponds to distances of closest approach between 0.6 a.u. and 0.17 a.u. We found that the charge of the Ar ions increases at internuclear distances less than 0.32 a.u.

  • 46. Jersblad, Johan
    et al.
    Ellmann, Harald
    Stockholm University, Faculty of Science, Department of Physics.
    Kastberg, Anders
    Experimental investigation of the limit of Sisyphus cooling2000In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 62, no 5Article in journal (Refereed)
    Abstract [en]

    We present measurements of the steady-state temperature in a three-dimensional cesium optical lattice, operating in the near-resonance regime of the D2 line. For various detunings between the (F-g=4 -->F-e=5) and the (F-g=4 -->F-e=4) transitions, we systematically determine at which intensities/optical potential modulation depths the Sisyphus cooling process breaks down and what the lowest achievable temperatures are. We find that the minimum temperature decreases as we increase the detuning with respect to the (F-g=4 -->F-e=5) transition.

  • 47.
    Johansson, Henrik A. B.
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Holm, Anne I. S.
    Stockholm University, Faculty of Science, Department of Physics.
    Seitz, Fabian
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Rousseau, P.
    Lawicki, A.
    Capron, M.
    Domaracka, A.
    Lattouf, E.
    Maclot, S.
    Maisonny, R.
    Manil, B.
    Chesnel, J.-Y.
    Adoui, L.
    Huber, B. A.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Ionization and fragmentation of polycyclic aromatic hydrocarbon clusters in collisions with keV ions2011In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 84, no 4, 043201- p.Article in journal (Refereed)
    Abstract [en]

    We report on an experimental study of the ionization and fragmentation of clusters of k polycyclic aromatic hydrocarbon (PAH) molecules using anthracene, C14H10, or coronene, C24H12. These PAH clusters are moderately charged and strongly heated in small impact parameter collisions with 22.5-keV He2+ ions, after which they mostly decay in long monomer evaporation sequences with singly charged and comparatively cold monomers as dominating end products. We describe a simple cluster evaporation model and estimate the number of PAH molecules in the clusters that have to be hit by He2+ projectiles for such complete cluster evaporations to occur. Highly charged and initially cold clusters are efficiently formed in collisions with 360-keV Xe20+ ions, leading to cluster Coulomb explosions and several hot charged fragments, which again predominantly yield singly charged, but much hotter, monomer ions than the He2+ collisions. We present a simple formula, based on density-functional-theory calculations, for the ionization energy sequences as functions of coronene cluster size, rationalized in terms of the classic electrostatic expression for the ionization of a charged conducting object. Our analysis indicates that multiple electron removal by highly charged ions from a cluster of PAH molecules rapidly may become more important than single ionization as the cluster size k increases and that this is the main reason for the unexpectedly strong heating in these types of collisions.

  • 48. Joshi, C.
    et al.
    Larson, Jonas
    Stockholm University, Faculty of Science, Department of Physics.
    Jonson, M.
    Andersson, E.
    Ohberg, P.
    Entanglement of distant optomechanical systems2012In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 85, no 3, 033805- p.Article in journal (Refereed)
    Abstract [en]

    We theoretically investigate the possibility to generate nonclassical states of optical and mechanical modes of optical cavities, distant from each other. A setup comprised of two identical cavities, each with one fixed and one movable mirror and coupled by an optical fiber, is studied in detail. We show that with such a setup there is potential to generate entanglement between the distant cavities, involving both optical and mechanical modes. The scheme is robust with respect to dissipation, and nonlocal correlations are found to exist in the steady state at finite temperatures.

  • 49.
    Kamińska, Magdalena
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Jan Kochanowski University, Poland.
    Davis, V. T.
    Hole, Odd Magnar
    Stockholm University, Faculty of Science, Department of Physics.
    Nascimento, Rodrigo F.
    Stockholm University, Faculty of Science, Department of Physics. Centro Federal de Educação Tecnológica Celso Suckow da Fonseca, Brazil.
    Chartkunchand, Kiattichart C.
    Stockholm University, Faculty of Science, Department of Physics. University of Nevada, USA.
    Blom, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Björkhage, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Källberg, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Löfgren, Patrik
    Stockholm University, Faculty of Science, Department of Physics.
    Reinhed, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Rosén, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    Simonsson, Ansgar
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Mannervik, Sven
    Stockholm University, Faculty of Science, Department of Physics.
    Neill, P. A.
    Thompson, J. S.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Hanstorp, D.
    Lifetime of the bound excited level in Ni-2016In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 93, no 1, 012512Article in journal (Refereed)
    Abstract [en]

    The intrinsic lifetime of the upper level in the bound-bound 3d(9) 4s(2) D-2(3/2) -> 3d(9) 4s(2) D-2(5/2) radiative transition in Ni- was measured to be 15.1 +/- 0.4 s. The experiment was performed at cryogenic temperatures in one of the ion-beam storage rings of the Double ElectroStatic Ion Ring ExpEriment facility at Stockholm University. The storage lifetime of the Ni- ion beam was measured to be close to 5 min at a ring temperature of 13 K.

  • 50.
    Kloda, Tomasz
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Matsuda, Akitaka
    Karlsson, Hans O.
    Elshakre, Mohamed
    Linusson, Per
    Stockholm University, Faculty of Science, Department of Physics.
    Eland, John H. D.
    Feifel, Raimund
    Hansson, Tony
    Stockholm University, Faculty of Science, Department of Physics.
    Strong-field photoionization of O-2 at intermediate light intensity2010In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 82, no 3, 33431- p.Article in journal (Refereed)
    Abstract [en]

    We investigated by electron spectroscopy the strong-field multiphoton ionization of O-2 molecules with ultrashort laser pulses in the intensity range between the multiphoton and tunneling regimes. The ionization proceeds by at least three different mechanisms, in addition to the eight- and nine-photon nonresonant pathways. Transient multiphoton resonances with vibrational Rydberg levels give rise to direct Freeman-type peaks with sublaser linewidth and spin-orbit splitting. Some resonance levels actually become populated and yield extremely narrow lines because of postpulse vibrational autoionization. When the lowest photon order resonance channel for the Rydberg states is closed, a third contribution becomes dominant with a main peak at 0.4 eV that shares its main properties with the recently discovered universal low-energy structure in the electron spectra of atoms and molecules [C. I. Blaga et al., Nat. Phys. 5, 335 (2009); W. Quan et al., Phys. Rev. Lett. 103, 093001 (2009)]. The variation of the Freeman resonance spectrum with the laser peak intensity is well correlated with the vibronic Franck-Condon factors for the overlap of the intermediate Rydberg state with the O-2 ground state. Accordingly, the Freeman peaks could be unambiguously assigned to individual vibronic multiphoton resonances, and the disappearance of the Freeman resonances at a certain laser intensity could be explained. The population of the autoionizing Rydberg states could be assigned similarly to such vibronic resonances.

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