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  • 1. Abascal, Isabel Sainz
    et al.
    Björk, Gunnar
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Bipartite entanglement measure based on covariance2007In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 75, no 6Article in journal (Refereed)
    Abstract [en]

    We propose an entanglement measure for two quNits based on the covariances of a set of generators of the su(N) algebra. In particular, we represent this measure in terms of the mutually unbiased projectors for N prime. For pure states this measure quantifies entanglement, we obtain an explicit expression which relates it to the concurrence hierarchy, specifically the I-concurrence and the three-concurrence. For mixed states we propose a separability criterion.

  • 2.
    Abdullaev, Fatkhulla
    et al.
    Physical-Technical Institute, Uzbek Academy of Sciences, Tashkent, Uzbekistan; Instituto de Fisica Teorica, Universidade Estadual Paulista Júlio de Mesquita Filho, São Paulo, Brazil.
    Ögren, Magnus
    Department of Applied Mathematics and Computer Science, Technical University of Denmark, Kongens Lyngby, Denmark.
    Sørensen, M. P.
    Department of Applied Mathematics and Computer Science, Technical University of Denmark, Kongens Lyngby, Denmark.
    Faraday waves in quasi-one-dimensional superfluid Fermi-Bose mixtures2013In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 87, no 2, article id 023616Article in journal (Refereed)
    Abstract [en]

    The generation of Faraday waves in superfluid Fermi-Bose mixtures in elongated traps is investigated. The generation of waves is achieved by periodically changing a parameter of the system in time. Two types of modulations of parameters are considered: a variation of the fermion-boson scattering length and the boson-boson scattering length. We predict the properties of the generated Faraday patterns and study the parameter regions where they can be excited.

  • 3.
    Abdullaev, Fatkhulla
    et al.
    Physical-Technical Institute, Uzbek Academy of Sciences, Tashkent, Uzbekistan; CNH, Universidade Federal do ABC, Santo André, Brazil.
    Ögren, Magnus
    Örebro University, School of Science and Technology. Nano Science Center, Department of Chemistry, University of Copenhagen, København, Denmark.
    Sørensen, Mads-Peter
    Department of Applied Mathematics and Computer Science, Technical University of Denmark, Kongens Lyngby, Denmark.
    Collective dynamics of Fermi-Bose mixtures with an oscillating scattering length2019In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 99, no 3, article id 033614Article in journal (Refereed)
    Abstract [en]

    Collective oscillations of superfluid mixtures of ultra cold fermionic and bosonic atoms are investigated while varying the fermion-boson scattering length. We study the dynamics with respect to excited center of mass modes and breathing modes in the mixture. Parametric resonances are also analyzed when the scattering length varies periodically in time, by comparing partial differential equation (PDE) models and ordinary differential equation (ODE) models for the dynamics. An application to the recent experiment with fermionic Li-6 and bosonic Li-7 atoms, which approximately have the same masses, is discussed.

  • 4. Acín, Antonio
    et al.
    Pironio, Stefano
    Vértesi, Tamás
    Wittek, Peter
    University of Borås, Faculty of Librarianship, Information, Education and IT.
    Optimal randomness certification from one entangled bit2016In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 93, no 4Article in journal (Refereed)
    Abstract [en]

    By performing local projective measurements on a two-qubit entangled state one can certify in a device-independent way up to one bit of randomness. We show here that general measurements, defined by positive-operator-valued measures, can certify up to two bits of randomness, which is the optimal amount of randomness that can be certified from an entangled bit. General measurements thus provide an advantage over projective ones for device-independent randomness certification.

  • 5. Adesso, Gerardo
    et al.
    Ericsson, Marie
    Centre for Quantum Computation, DAMTP, University of Cambridge, UK.
    Entanglement in Gaussian matrix-product states2006In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 74, no 3, p. 030305(R)-Article in journal (Refereed)
    Abstract [en]

    Gaussian matrix product states are obtained as the outputs of projection operations from an ancillary space of M infinitely entangled bonds connecting neighboring sites, applied at each of N sites of an harmonic chain. Replacing the projections by associated Gaussian states, the 'building blocks', we show that the entanglement range in translationally-invariant Gaussian matrix product states depends on how entangled the building blocks are. In particular, infinite entanglement in the building blocks produces fully symmetric Gaussian states with maximum entanglement range. From their peculiar properties of entanglement sharing, a basic difference with spin chains is revealed: Gaussian matrix product states can possess unlimited, long-range entanglement even with minimum number of ancillary bonds (M=1). Finally we discuss how these states can be experimentally engineered from N copies of a three-mode building block and N two-mode finitely squeezed states.

  • 6. Adesso, Gerardo
    et al.
    Ericsson, Marie
    Centre for Quantum Computation, DAMTP, University of Cambridge, UK.
    Illuminati, Fabrizio
    Coexistence of unlimited bipartite and genuine multipartite entanglement: Promiscuous quantum correlations arising from discrete to continuous variable systems2007In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 76, no 2, p. 022315-Article in journal (Refereed)
    Abstract [en]

    Quantum mechanics imposes 'monogamy' constraints on the sharing of entanglement. We show that, despite these limitations, entanglement can be fully 'promiscuous', i.e. simultaneously present in unlimited two-body and many-body forms in states living in an infinite-dimensional Hilbert space. Monogamy just bounds the divergence rate of the various entanglement contributions. This is demonstrated in simple families of N-mode (N >= 4) Gaussian states of light fields or atomic ensembles, which therefore enable infinitely more freedom in the distribution of information, as opposed to systems of individual qubits. Such a finding is of importance for the quantification, understanding and potential exploitation of shared quantum correlations in continuous variable systems. We discuss how promiscuity gradually arises when considering simple families of discrete variable states, with increasing Hilbert space dimension towards the continuous variable limit. Such models are somehow analogous to Gaussian states with asymptotically diverging, but finite squeezing. In this respect, we find that non-Gaussian states (which in general are more entangled than Gaussian states), exhibit also the interesting feature that their entanglement is more shareable: in the non-Gaussian multipartite arena, unlimited promiscuity can be already achieved among three entangled parties, while this is impossible for Gaussian, even infinitely squeezed states.

  • 7.
    Adesso, Gerardo
    et al.
    Dipartimento di Fisica “E. R. Caianiello”, Universit`a degli Studi di Salerno, Baronissi, Italy.
    Fuentes-Schuller, Ivette
    Instituto de Ciencias Nucleares, Universidad Nacional Aut´onoma de M´exico, Mexico.
    Ericsson, Marie
    Centre for Quantum Computation, DAMTP, University of Cambridge, UK.
    Continuous variable entanglement sharing in noninertial frames2007In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 76, no 6, p. 062112-Article in journal (Refereed)
    Abstract [en]

    We study the distribution of entanglement between modes of a free scalar field from the perspective of observers in uniform acceleration. We consider a two-mode squeezed state of the field from an inertial perspective, and analytically study the degradation of entanglement due to the Unruh effect, in the cases of either one or both observers undergoing uniform acceleration. We find that for two observers undergoing finite acceleration, the entanglement vanishes between the lowest frequency modes. The loss of entanglement is precisely explained as a redistribution of the inertial entanglement into multipartite quantum correlations among accessible and unaccessible modes from a non-inertial perspective. We show that classical correlations are also lost from the perspective of two accelerated observers but conserved if one of the observers remains inertial.

  • 8.
    Ahufinger, V.
    et al.
    Grup d’Òptica, Departament de Física, Universitat Autònoma de Barcelona, E-08193 Belaterra, Barcelona, Spain;Institut für Theoretische Physik, Universität Hannover, D-30167 Hannover, Germany.
    Sanchez-Palencia, L.
    Institut für Theoretische Physik, Universität Hannover, D-30167 Hannover, Germany;Laboratoire Charles Fabry, Institut d’Optique Théorique et Appliquée, Université Paris-Sud XI, F-91403 Orsay Cedex, France.
    Kantian, A.
    Institut für Theoretische Physik, Universität Hannover, D-30167 Hannover, Germany;Institut für Quantenoptik und Quanteninformation der Österreichischen, Akademie der Wissenschaften, A-6020 Innsbruck, Austria;Institut für Theoretische Physik, Universität Innsbruck, A-6020 Innsbruck, Austria.
    Sanpera, A.
    Institut für Theoretische Physik, Universität Hannover, D-30167 Hannover, Germany;Grup de Física Teòrica, Departament de Física, Universitat Autònoma de Barcelona, E-08193 Belaterra, Barcelona, Spain.
    Lewenstein, M.
    Institut für Theoretische Physik, Universität Hannover, D-30167 Hannover, Germany;Institut de Ciències Fotòniques, E-08034 Barcelona, Spain.
    Disordered ultracold atomic gases in optical lattices: A case study of Fermi-Bose mixtures2005In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 72, no 6Article in journal (Refereed)
    Abstract [en]

    We present a review of properties of ultracold atomic Fermi-Bose mixtures in inhomogeneous and random optical lattices. In the strong interacting limit and at very low temperatures, fermions form, together with bosons or bosonic holes, composite fermions. Composite fermions behave as a spinless interacting Fermi gas, and in the presence of local disorder they interact via random couplings and feel effective random local potential. This opens a wide variety of possibilities of realizing various kinds of ultracold quantum disordered systems. In this paper we review these possibilities, discuss the accessible quantum disordered phases, and methods for their detection. The discussed quantum phases include Fermi glasses, quantum spin glasses, “dirty” superfluids, disordered metallic phases, and phases involving quantum percolation.

  • 9. Allahverdyan, A
    et al.
    Khrennikov, Andrei
    Växjö University, Faculty of Mathematics/Science/Technology, School of Mathematics and Systems Engineering.
    Nieuwenhuizen, Th. M
    Brownian entanglement2005In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 72, p. 032102-Article in journal (Refereed)
  • 10. Andersen, T.
    et al.
    Keller, O.
    Hubner, W.
    Johansson, Börje
    Spin and diamagnetism in linear and nonlinear optics2004In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 70, no 4Article in journal (Refereed)
  • 11. 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, p. 043418-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.

  • 12. Andersson, E.
    et al.
    Linusson, P.
    Fritzsche, S.
    Hedin, Lage
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
    Eland, John H. D.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
    Karlsson, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
    Rubensson, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
    Feifel, Raimund
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
    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, p. 032502-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.

  • 13. 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, p. 032502-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.

  • 14. Andersson, E.
    et al.
    Stenrup, Michael
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Eland, J.H.D.
    Hedin, L.
    Berglund, M.
    Karlsson, L.
    Larson, Åsa
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Rubensson, Jan Erik
    Feifel, Raimund
    Single-photon core-valence double ionization of molecular oxygen2008In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 78, no 2, 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-1 V-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 Π3 dicationic state.

  • 15.
    Andersson, Egil
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
    Fritzsche, Stephan
    Linusson, Per
    Hedin, Lage
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
    Eland, John H. D.
    Rubensson, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
    Karlsson, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
    Feifel, Raimund
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
    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, p. 043418-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.

  • 16.
    Andersson, Egil
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Soft X-Ray Physics.
    Stenrup, M.
    Eland, J. H. D.
    Hedin, L.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Soft X-Ray Physics.
    Berglund, M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Karlsson, L.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Soft X-Ray Physics.
    Larson, A.
    Ågren, H.
    Rubensson, J. -E.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Soft X-Ray Physics.
    Feifel, R.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Soft X-Ray Physics.
    Single-photon core-valence double ionization of molecular oxygen2008In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 78, no 2, 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 O-2 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)Pi dicationic state.

  • 17. Andersson, Erika
    et al.
    Stenholm, Stig
    KTH, School of Engineering Sciences (SCI), Physics.
    Variational properties of a pumped dynamical system2010In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 81, no 2, p. 022111-Article in journal (Refereed)
    Abstract [en]

    We earlier constructed a generalized entropy concept to show the direction of time in an evolution following from a Markov generator. In such a dynamical system the entity found changes in a monotonic way starting from any initial state of the system. In this article, we generalize the treatment to the case when population is pumped into the system from levels not explicitly considered. These populations then pass through the coupled levels and exit by decay to levels outside the system. We derive the form of the equation of motion and relate it to our earlier treatments. It turns out that the formalism can be generalized to the new situation. Its physically relevant features are demonstrated and the behavior obtained is illustrated by a numerical treatment of the standard two-level system with pumping and relaxation included.

  • 18. Andersson, J.
    et al.
    Beerwerth, R.
    Linusson, P.
    Eland, J. H. D.
    Zhaunerchyk, V.
    Fritzsche, S.
    Feifel, Raimund
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    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, article id 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.

  • 19. 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, article id 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.

  • 20. Andersson, L M
    et al.
    Burmeister, F
    Karlsson, H O
    Goscinski, O
    Nonadiabatic effects in the photoelectron spectra of HCl and DCl. II. Theory2002In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 65, no 1, p. 012705-Article in journal (Refereed)
    Abstract [en]

    The vibrationally resolved photoelectron spectra of HCl and DCl in the 25-28 eV region were computed using a time-dependent approach for the nuclear dynamics. The spectral features cannot be understood without including a nonadiabatic coupling between the dissociative 3 (2)Sigma(+) state and the bound 4 (2)Sigma(+) state in the adiabatic picture. Alternatively, in the diabatic picture a dissociative two-hole-one-particle state interacts with a bound one-hole state. The molecular system is of intermediate coupling strength, i.e., it cannot be described by a single potential-energy curve. The interaction between a bound and a dissociative state leads to Fano resonances superimposed on a broad back-round, as observed in the experimental spectra [Burmeister et al., Phys. Rev. A 65, 012704 (2001)]. From modified potential-energy curves, all features of the experimental spectra, including Fano resonance parameters and lifetimes, were reproduced. From the simulations we observe that two additional peaks in the experimental DCl spectra should appear if the resolution were to be enhanced to around 10 meV.

  • 21. Andersson, L. Mauritz
    et al.
    Burmeister, F.
    Karlsson, H. O.
    Goscinski, O.
    Nonadiabatic effects in the photoelectron spectra of HCl and DCl. II. Theory2002In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 65, no 1Article in journal (Refereed)
    Abstract [en]

    The vibrationally resolved photoelectron spectra of HCl and DCl in the 25-28 eV region were computed using a time-dependent approach for the nuclear dynamics. The spectral features cannot be understood without including a nonadiabatic coupling between the dissociative 3 (2)Sigma(+) state and the bound 4 (2)Sigma(+) state in the adiabatic picture. Alternatively, in the diabatic picture a dissociative two-hole-one-particle state interacts with a bound one-hole state. The molecular system is of intermediate coupling strength, i.e., it cannot be described by a single potential-energy curve. The interaction between a bound and a dissociative state leads to Fano resonances superimposed on a broad back-round, as observed in the experimental spectra [Burmeister et al., Phys. Rev. A 65, 012704 (2001)]. From modified potential-energy curves, all features of the experimental spectra, including Fano resonance parameters and lifetimes, were reproduced. From the simulations we observe that two additional peaks in the experimental DCl spectra should appear if the resolution were to be enhanced to around 10 meV.

  • 22. Andersson, P.
    et al.
    Fritioff, K.
    Sandström, J.
    Collins, G.
    Hanstorp, D.
    Ellmann, A.
    Schef, P.
    Lundin, P.
    Mannervik, S.
    Royen, P.
    Fischer, F. K. C.
    Österdahl, Fabian
    KTH, School of Engineering Sciences (SCI), Physics.
    Rostohar, D.
    Pegg, D. J.
    Gibson, N. D.
    Danared, H.
    Källberg, A.
    Radiative lifetimes of metastable states of negative ions2006In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 73, no 3, p. 032705-Article in journal (Refereed)
    Abstract [en]

    We present a technique for measuring the radiative lifetimes of metastable states of negative ions that involves the use of a heavy-ion storage ring. The method has been applied to investigate the radiative decay of the np(3) P-2(1/2) levels of Te-(n=5) and Se-(n=4) and the 3p(3) D-2 state of Si- for which the J=3/2 and 5/2 levels were unresolved. All of these states are metastable and decay primarily by emission of E2 and M1 radiation. Multi Configuration Dirac-Hartree-Fock calculations of rates for the transitions in Te- and Se- yielded lifetimes of 0.45 s and 4.7 s, respectively. The measured values agree well with these predicted values. In the case of the D-2 state of Si-, however, our measurement was only able to set a lower limit on the lifetime. The upper limit of the lifetime that can be measured with our apparatus is set by how long the ions can be stored in the ring, a limit determined by the rate of collisional detachment. Our lower limit of 1 min for the lifetime of the D-2 state is consistent with both the calculated lifetimes of 162 s for the D-2(3/2) level and 27.3 h for the D-2(5/2) level reported by O'Malley and Beck and 14.5 h and 12.5 h, respectively, from our Breit-Pauli calculations.

  • 23. 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, p. 032107-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.

  • 24. 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.

  • 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. Arteca, Gustavo A.
    et al.
    Tapia, Orlando
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
    Quantum states for quantum processes: A toy model for ammonia inversion spectra2011In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 84, no 1, p. 012115-Article in journal (Refereed)
    Abstract [en]

    Chemical transformations are viewed here as quantum processes modulated by external fields, that is, as shifts in reactant to product amplitudes within a quantum state represented by a linear (coherent) superposition of electronuclear basis functions; their electronic quantum numbers identify the "chemical species." This basis set can be mapped from attractors built from a unique electronic configurational space that is invariant with respect to the nuclear geometry. In turn, the quantum numbers that label these basis functions and the semiclassical potentials for the electronic attractors may be used to derive reaction coordinates to monitor progress as a function of the applied field. A generalization of Feynman's three-state model for the ammonia inversion process illustrates the scheme; to enforce symmetry for the entire inversion process model and ensure invariance with respect to nuclear configurations, the three attractors and their basis functions are computed with a grid of fixed floating Gaussian functions. The external-field modulation of the effective inversion barrier is discussed within this conceptual approach. This analysis brings the descriptions of chemical processes near modern technologies that employ molecules to encode information by means of confinement and external fields.

  • 27.
    Arve, Per
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Jänes, Peter
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Thylén, Lars
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Propagation of two-dimensional pulses in electromagnetically induced transparency media2004In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 69, no 6, p. 063809-Article in journal (Refereed)
    Abstract [en]

    The propagation in two dimensions of "optical" pulses in electromagnetically induced transparency media is analyzed. Results are presented for coupled Maxwell-Bloch equations with slowly varying envelope approximation, for both adiabatic and nonadiabatic situations. The possibility of changing the direction of the pulse by a switch of control beam direction is investigated in detail.

  • 28. Asboth, Janos K.
    et al.
    Edge, Jonathan M.
    KTH, Centres, 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, article id 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.

  • 29. 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, article id 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.

  • 30. Asplund, R.
    et al.
    Björk, Gunnar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Reconstructing the discrete Wigner function and some properties of the measurement bases2001In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 6401, no 1Article in journal (Refereed)
    Abstract [en]

    We derive a direct reconstruction algorithm for the discrete Wigner function through different types of measurements. For a system described in a Hilbert space of dimension N=N-1...N-p, where the numbers N-i are prime, the reconstruction is accomplished with (N-1+1)...(N-p+1) factorable (local) von Neumann measurements. For the special case where the dimension is a power of a prime, the reconstruction can be performed in a much more efficient way using N+1 complementary measurements. If the system is composed of a number of smaller subsystems, these measurements will then in general be nonseparable.

  • 31.
    Azimi Mousolou, Vahid
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Computer Science, Physics and Mathematics.
    Canali, Carlo M.
    Linnaeus University, Faculty of Science and Engineering, School of Computer Science, Physics and Mathematics.
    Sjöqvist, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Quantum Chemistry) (Quantum information theory.
    Non-Abelian quantum holonomy of hydrogen-like atoms2011In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, ISSN 1050-2947, Vol. 84, no 3, p. Article ID: 032111-Article in journal (Refereed)
    Abstract [en]

    We study the Uhlmann holonomy [Rep. Math. Phys. 24, 229 (1986)] of quantum states for hydrogen-like atoms, where the intrinsic spin and orbital angular momentum are coupled by the spin-orbit interaction and subject to a slowly varying magnetic field. We show that the holonomy for the orbital angular momentum and spin subsystems is non-Abelian, while the holonomy of the whole system is Abelian. Quantum entanglement in the states of the whole system is crucially related to the non-Abelian gauge structure of the subsystems. We analyze the phase of the Wilson loop variable associated with the Uhlmann holonomy, and find a relation between the phase of the whole system with corresponding marginal phases. Based on the result for the model system we provide evidence that the phase of the Wilson loop variable and the mixed-state geometric phase [Phys. Rev. Lett. 85, 2845 (2000)] are in general inequivalent.

  • 32.
    Azimi Mousolou, Vahid
    et al.
    School of Computer Science, Physics and Mathematics, Linnaeus Univ., Sweden.
    Canali, Carlo M.
    School of Computer Science, Physics and Mathematics, Linnaeus Univ., Sweden.
    Sjöqvist, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Quantum Chemistry.
    Non-Abelian quantum holonomy of hydrogen-like atoms2011In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 84, no 3, article id 032111Article in journal (Refereed)
    Abstract [en]

    We study the Uhlmann holonomy [Rep. Math. Phys. 24, 229 (1986)] of quantum states for hydrogen-like atoms, where the intrinsic spin and orbital angular momentum are coupled by the spin-orbit interaction and subject to a slowly varying magnetic field. We show that the holonomy for the orbital angular momentum and spin subsystems is non-Abelian, while the holonomy of the whole system is Abelian. Quantum entanglement in the states of the whole system is crucially related to the non-Abelian gauge structure of the subsystems. We analyze the phase of the Wilson loop variable associated with the Uhlmann holonomy, and find a relation between the phase of the whole system with corresponding marginal phases. Based on the result for the model system we provide evidence that the phase of the Wilson loop variable and the mixed-state geometric phase [Phys. Rev. Lett. 85, 2845 (2000)] are in general inequivalent.

  • 33.
    Azimi Mousolou, Vahid
    et al.
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Canali, Carlo M.
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Sjöqvist, Erik
    Department of Quantum Chemistry, Uppsala University, Box 518, Se-751 20 Uppsala, Sweden.
    Unifying geometric entanglement and geometric phase in a quantum phase transition2013In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 88, no 1, p. Article ID: 012310-Article in journal (Refereed)
    Abstract [en]

    Geometric measure of entanglement and geometric phase have recently been used to analyze quantum phase transition in the XY spin chain. We unify these two approaches by showing that the geometric entanglement and the geometric phase are respectively the real and imaginary parts of a complex-valued geometric entanglement, which can be investigated in typical quantum interferometry experiments. We argue that the singular behavior of the complex-valued geometric entanglement at a quantum critical point is a characteristic of any quantum phase transition, by showing that the underlying mechanism is the occurrence of level crossings associated with the underlying Hamiltonian.

  • 34.
    Azimi Mousolou, Vahid
    et al.
    School of Computer Science, Physics and Mathematics, Linnaeus Univ., Sweden.
    Canali, Carlo M.
    School of Computer Science, Physics and Mathematics, Linnaeus Univ., Sweden.
    Sjöqvist, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry. Centre for Quantum Technologies, NUS, Singapore.
    Unifying Geometric Entanglement and Geometric Phase in a Quantum Phase Transition2013In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 88, no 1, p. 012310-Article in journal (Refereed)
    Abstract [en]

    Geometric measure of entanglement and geometric phase have recently been used to analyze quantum phase transition in the XY spin chain. We unify these two approaches by showing that the geometric entanglement and the geometric phase are respectively the real and imaginary parts of a complex-valued geometric entanglement, which can be investigated in typical quantum interferometry experiments. We argue that the singular behavior of the complex-value geometric entanglement at a quantum critical point is a characteristic of any quantum phase transition, by showing that the underlying mechanism is the occurrence of level crossings associated with the underlying Hamiltonian.

  • 35.
    Azimi Mousolou, Vahid
    et al.
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Sjöqvist, Erik
    Uppsala Univ.
    Non-Abelian geometric phases in a system of coupled quantum bits2014In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 89, no 2, p. 022117-Article in journal (Refereed)
    Abstract [en]

    A common strategy to measure the Abelian geometric phase for a qubit is to let it evolve along an orange-slice-shaped path connecting two antipodal points on the Bloch sphere by two different semi-great-circles. Since the dynamical phases vanish for such paths, this allows for direct measurement of the geometric phase. Here, we generalize the "orange-slice" setting to the non-Abelian case. The proposed method to measure the non-Abelian geometric phase can be implemented in a cyclic chain of four qubits with controllable interactions.

  • 36.
    Azimi Mousolou, Vahid
    et al.
    School of Computer Science, Physics and Mathematics, Linnaeus Univ., Sweden.
    Sjöqvist, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Non-Abelian geometric phases in a system of coupled quantum bits2014In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 89, no 2, p. 022117-Article in journal (Refereed)
    Abstract [en]

    A common strategy to measure the Abelian geometric phase for a qubit is to let it evolve along an `orange slice' shaped path connecting two antipodal points on the Bloch sphere by two different semi-great circles. Since the dynamical phases vanish for such paths, this allows for direct interference measurement of the geometric phase. Here, we generalize the orange slice setting to the non-Abelian case. The proposed method to measure the non-Abelian geometric phase can be implemented in a cyclic chain of four qubits with controllable nearest-neighbor interactions.

  • 37.
    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, p. 012301-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.

  • 38.
    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, p. 010301-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.

  • 39. Baev, A.
    et al.
    Feifel, R.
    Gel'mukhanov, Faris
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Piancastelli, M. N.
    Bassler, M.
    Miron, C.
    Sorensen, S. L.
    de Brito, A. N.
    Bjorneholm, O.
    Karlsson, L.
    Svensson, S.
    Geometrical information on core-excited states obtained from interference quenching of vibrational states in resonant x-ray photoemission2003In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 67, no 2Article in journal (Refereed)
    Abstract [en]

    An interference quenching of the m=1 final state vibrational line in the resonant Auger decay of N 1s-->pi(*) core-excited N-2 is observed and analyzed. The intensity ratio between the m=1 and m=0 vibrational levels of the X (2)Sigma(g)(+) final state shows a surprising nonmonotonic variation as a function of frequency detuning, going through a minimum with a complete suppression of m=1. We have developed a simple model which indicates a linear relation between the value of the detuning frequency for this minimum and the equilibrium bond distance of the core-excited state. This implies the possibility of determining the equilibrium bond distances for core-excited states to a high degree of accuracy. Simultaneously with the simple model we present a strict theory of the studied effect. This strict theory allows us to explore the accuracy of determining the bond length of the core-excited state from resonant Auger spectra. We obtain a weak influence of the core-hole lifetime on the determined bond length, whereas the number of intermediate vibrational states accounted for in the numerical simulations seems to be quite important.

  • 40. Baev, A.
    et al.
    Gel'mukhanov, Faris
    KTH, Superseded Departments, Biotechnology.
    Salek, Pawel
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Ueda, K.
    de Fanis, A.
    Okada, K.
    Sorensen, S.
    Doppler interference in dissociative resonant photoemission2002In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 66, no 2Article in journal (Refereed)
    Abstract [en]

    Resonant photoemission involving dissociative core excited states has been the subject of a great number of experimental and theoretical investigations in recent time. The resonant decay of such dissociating systems has been shown to lead to semiatomic Auger electron emission spectra, with particular angular behavior. In the present paper a detailed theoretical analysis of dissociative resonant photoemission spectra of homonuclear diatomic molecules is presented. The theory addresses both fixed in space and randomly oriented homonuclear molecules and emphasizes the Doppler effect and the role of the interference between channels referring to the Doppler split atomic fragments. It is shown that peaks originating from decay in the atomic fragments can be asymmetric and structured due to the Doppler interference effect. The predicted strong non-Lorentzian behavior of the substructure on the top of the Doppler broadened atomiclike contribution is traced to the interplay between decay channels leading to gerade and ungerade final states. Simulations based on wave-packet theory are compared with experimental data for molecular oxygen. Our numerical simulations of the atomiclike resonance of fixed in space molecules show that the spectral profile is very sensitive to the shape of interatomic potentials of core excited and final states. It is shown that the Doppler effect in the decay spectra depends upon the symmetry of the core excited state.

  • 41.
    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.

  • 42. 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, p. 52703-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.

  • 43. Bao, Fanglin
    et al.
    Evans, Julian S.
    Fang, Maodong
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. Zhejiang University, China; South China Normal University, China .
    Inhomogeneity-related cutoff dependence of the Casimir energy and stress2016In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 93, no 1, article id 013824Article in journal (Refereed)
    Abstract [en]

    The Casimir stress and energy density are widely used to study the Casimir force, but they diverge in inhomogeneous systems, making the force seem to be infinite as well. Here we characterize the asymptotic behavior of the Casimir stress and energy density in inhomogeneous systems. We show an unambiguous map of all cutoff-dependent terms in the asymptotic expansion to the pressure and the surface tension through the insertion of multiple boundary layers. This result reveals an elegant subtraction to retrieve a finite stress that yields a cutoff-independent force.

  • 44. Bao, Fanglin
    et al.
    Luo, Bin
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    First-order correction to the Casimir force within an inhomogeneous medium2015In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 91, no 6, article id 063810Article in journal (Refereed)
    Abstract [en]

    For the Casimir piston filled with an inhomogeneous medium, we regularized and expressed the Casimir energy with cylinder kernel coefficients by using the first-order perturbation theory. When the refractive index of the medium is smoothly inhomogeneous (i.e., derivatives of all orders exist), a logarithmically cutoff-dependent term and a quadratically cutoff-dependent term in the Casimir energy are found. We show that in the piston model these terms vanish in the force and thus the Casimir force is always cutoff independent, but these terms will remain in the force in the half-space model and must be removed by additional regularizations. We give explicit benchmark solutions to the first-order corrections of both Casimir energy and Casimir force for an exponentially decaying profile. The present method can be extended to other inhomogeneous profiles. Our results should be useful for future relevant calculations and experimental studies.

  • 45. 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, article id 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.

  • 46.
    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.

  • 47. Baym, Gordon
    et al.
    Pethick, Christopher J.
    KTH, Centres, 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, p. 023602-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.

  • 48. 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, p. 023602-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.

  • 49. Baym, Gordon
    et al.
    Pethick, Christopher J.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    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. [New J. Phys. 13, 035003 (2011)].

  • 50. Belyaev, A. K.
    et al.
    Barklem, Paul S.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    Dickinson, A. S.
    Gadea, F. X.
    Cross sections for low-energy inelastic H plus Na collisions2010In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 81, no 3, p. 032706-Article in journal (Refereed)
    Abstract [en]

    Full quantum-scattering calculations are reported for low-energy near-threshold inelastic collision cross sections for H + Na. The calculations include transitions between all levels up to and including the ionic state (ion-pair production) for collision energies from the threshold up to 10 eV. These results are important for astrophysical modeling of spectra in stellar atmospheres. Results for the 3s-3p excitation are carefully examined using three different quantum chemistry input data sets, and large differences are found near the threshold. The differences are found to be predominantly due to differences in the radial coupling rather than potentials and are also found not to relate to differences in couplings in a simple manner. In fact, of the three input couplings, the two that are most similar give the cross sections with the largest differences. The 3s-3p cross sections show orbiting resonances which have been seen in earlier studies, while Feshbach resonances associated with closed channels were also found to be present in the low-energy cross sections for some transitions.

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