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  • 1.
    Anderson, Emma K.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Kamińska, Magdalena
    Stockholm University, Faculty of Science, Department of Physics. Jan Kochanowski University, Poland.
    Chartkunchand, Kiattichart C.
    Stockholm University, Faculty of Science, Department of Physics.
    Eklund, Gustav
    Stockholm University, Faculty of Science, Department of Physics.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics. University of Innsbruck, Austria.
    Hansen, K.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Decays of excited silver-cluster anions Ag-n, n=4 to 7, in the Double ElectroStatic Ion Ring ExpEriment2018In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 98, no 2, article id 022705Article in journal (Refereed)
    Abstract [en]

    Spontaneous decays of small, hot silver-cluster anions Ag-n(-), n = 4-7, have been studied using one of the rings of the Double ElectroStatic Ion Ring ExpEriment (DESIREE). Observation of these decays over very long time scales is possible due to the very low residual gas pressure (similar to 10(-14)) and cryogenic (13 K) operation of DESIREE. The yield of neutral particles from stored beams of Ag-6(-) and Ag-2(-) anions were measured for 100 milliseconds and were found to follow single power-law behavior with millisecond time-scale exponential cutoffs. The Ag-4(-) and Ag-5(-) anions were stored for 60 s and the observed decays show two-component power-law behaviors. We present calculations of the rate constants for electron detachment from and fragmentation of Ag-4(-) and Ag-5(-). In these calculations, we assume that the internal energy distribution of the clusters are flat and with this we reproduce the early steep parts of the experimentally measured decay curves for Ag-4(-) and Ag-5(-) which extends to tens and hundreds of milliseconds, respectively. The fact that the calculations reproduce the early slopes of Ag-4(-) and Ag-5(-), which differ for the two cases, suggests that it is the changes in fragmentation rates with internal cluster energies of Ag-4(-) and Ag-5(-) rather than conditions in the ion source that determine this behavior. Comparisons with the measurements strongly suggest that the neutral particles detected in these time domains originate from Ag-4(-) -> Ag-3(-) + Ag and Ag-5(-) -> Ag-3(-) +Ag-2 fragmentation processes.

  • 2.
    Anwer, Hammad
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Nawareg, Mohamed
    Stockholm University, Faculty of Science, Department of Physics. Damietta University, Egypt.
    Cabello, Adán
    Bourennane, Mohamed
    Stockholm University, Faculty of Science, Department of Physics.
    Experimental test of maximal tripartite nonlocality using an entangled state and local measurements that are maximally incompatible2019In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 100, no 2, article id 022104Article in journal (Refereed)
    Abstract [en]

    The only known qubit states that produce maximal quantum violation of a tight Bell inequality with maximally incompatible local measurements are Bell states, Greenberger-Horne-Zeilinger states, and a recently identified three-qubit state called vertical bar S >. Here we report the results of an experiment for preparing vertical bar S > and testing the maximum quantum violation of the corresponding tripartite Bell inequality. Using a heralded source of three entangled photons and three tunable polarization-dependent filters, we experimentally prepare vertical bar S > with 0.924 fidelity. Using maximally incompatible measurements for the three parties, we observe a value of T-26 = 7.30 +/- 0.06, which clearly violates the tight Bell inequality T-26 <= 5. In addition, we show that our setup allows preparing multipartite states that were inaccessible with previous methods and are useful for quantum information and metrology.

  • 3.
    Carlström, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Bergholtz, Emil J.
    Stockholm University, Faculty of Science, Department of Physics.
    Exceptional links and twisted Fermi ribbons in non-Hermitian systems2018In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 98, no 4, article id 042114Article in journal (Refereed)
    Abstract [en]

    The generic nature of band touching points in three-dimensional band structures is at the heart of the rich phenomenology, topological stability, and novel Fermi arc surface states associated with Weyl semimetals. Here we report on the corresponding scenario emerging in systems effectively described by non-Hermitian Hamiltonians. Remarkably, three-dimensional non-Hermitian systems have generic band touching along one-dimensional closed contours, forming exceptional rings and links in reciprocal space. The associated Seifert surfaces support open Fermi ribbons where the real part of the energy gap vanishes, providing a novel class of higher-dimensional bulk generalizations of Fermi arcs which are characterized by an integer twist number. These results have possible applications to a plethora of physical settings, ranging from mechanical systems and optical metamaterials with loss and gain to heavy fermion materials with finite-lifetime quasiparticles. In particular, photonic crystals provide fertile ground for simulating the exuberant phenomenology of exceptional links and their concomitant Fermi ribbons.

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

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

  • 5.
    Dai, Jin
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Niemi, Antti J.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Uppsala University, Sweden; Beijing Institute of Technology, China; Far Eastern Federal University, Russia.
    Peng, Xubiao
    Wilczek, Frank
    Stockholm University, Faculty of Science, Department of Physics. MIT, USA; Shanghai Jiao Tong University, China; Arizona State University, USA.
    Truncated dynamics, ring molecules, and mechanical time crystals2019In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 99, no 2, article id 023425Article in journal (Refereed)
    Abstract [en]

    We identify circumstances where the effective descriptions of microscopic physical systems leads to a self-consistent reduced dynamics for a truncated subset of the original variables. The effective Hamiltonian involves unusual Poisson brackets that bring in noncommutative geometry. In idealized models of ring molecules, we find time crystal behavior is widespread.

  • 6. Eckert, Sebastian
    et al.
    da Cruz, Vinícius Vaz
    Gel'mukhanov, Faris
    Ertan, Emelie
    Stockholm University, Faculty of Science, Department of Physics.
    Ignatova, Nina
    Polyutov, Sergey
    Couto, Rafael C.
    Fondell, Mattis
    Dantz, Marcus
    Kennedy, Brian
    Schmitt, Thorsten
    Pietzsch, Annette
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Föhlisch, Alexander
    One-dimensional cuts through multidimensional potential-energy surfaces by tunable x rays2018In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 97, no 5, article id 053410Article in journal (Refereed)
    Abstract [en]

    The concept of the potential-energy surface (PES) and directional reaction coordinates is the backbone of our description of chemical reaction mechanisms. Although the eigenenergies of the nuclear Hamiltonian uniquely link a PES to its spectrum, this information is in general experimentally inaccessible in large polyatomic systems. This is due to (near) degenerate rovibrational levels across the parameter space of all degrees of freedom, which effectively forms a pseudospectrum given by the centers of gravity of groups of close-lying vibrational levels. We show here that resonant inelastic x-ray scattering (RIXS) constitutes an ideal probe for revealing one-dimensional cuts through the ground-state PES of molecular systems, even far away from the equilibrium geometry, where the independent-mode picture is broken. We strictly link the center of gravity of close-lying vibrational peaks in RIXS to a pseudospectrum which is shown to coincide with the eigenvalues of an effective one-dimensional Hamiltonian along the propagation coordinate of the core-excited wave packet. This concept, combined with directional and site selectivity of the core-excited states, allows us to experimentally extract cuts through the ground-state PES along three complementary directions for the showcase H2O molecule.

  • 7.
    Gagge, Axel
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Larson, Jonas
    Stockholm University, Faculty of Science, Department of Physics.
    Bloch-like energy oscillations2018In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 98, no 5, article id 053820Article in journal (Refereed)
    Abstract [en]

    We identify a type of periodic evolution that appears in driven quantum systems. Provided that the instantaneous (adiabatic) energies are equidistant we show how such systems can be mapped to (time-dependent) tilted single-band lattice models. Having established this mapping, the dynamics can be understood in terms of Bloch oscillations in the instantaneous energy basis. In our lattice model the site-localized states are the adiabatic ones, and the Bloch oscillations manifest as a periodic repopulation among these states, or equivalently a periodic change in the system's instantaneous energy. Our predictions are confirmed by considering two different models: a driven harmonic oscillator and a Landau-Zener grid model. To strengthen the link between our energy Bloch oscillations and the original spatial Bloch oscillations we add a random disorder that breaks the translational invariance of the spectrum. This verifies that the oscillating evolution breaks down and instead turns into a diffusive spreading. Finally, we consider a trapped ion setup and demonstrate how the mechanism can be utilized to prepare motional cat state of the ion.

  • 8.
    Gatchell, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Universität Innsbruck, Austria.
    Martini, Paul
    Kranabetter, Lorenz
    Rasul, Bilal
    Scheier, Paul
    Magic sizes of cationic and protonated argon clusters2018In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 98, no 2, article id 022519Article in journal (Refereed)
    Abstract [en]

    There has long been a discrepancy between the size distributions of Ar-n(+) clusters measured by different groups regarding whether or not magic numbers appear at sizes corresponding to the closure of icosahedral (sub-) shells. We show that the previously observed magic cluster size distributions are likely the result of an unresolved ArnH+ component, i.e., from protonated argon clusters. We find that the proton impurity gives cluster geometries that are much closer to those for neutral rare-gas clusters, which are known to form icosahedral structures, than for the pure cationic clusters, explaining why the mass spectra from protonated argon clusters better matches these structural models. Our results thus show that even small impurities, e.g., a single proton, can significantly influence the properties of clusters.

  • 9. Gumberidze, A.
    et al.
    Thorn, D. B.
    Surzhykov, A.
    Fontes, C. J.
    Najjari, B.
    Voitkiv, A.
    Fritzsche, S.
    Banas, D.
    Beyer, H. F.
    Chen, W.
    Grisenti, R. E.
    Hagmann, S.
    Hess, R.
    Hillenbrand, P. -M.
    Indelicato, P.
    Kozhuharov, C.
    Lestinsky, M.
    Maertin, R.
    Petridis, N.
    Popov, R. V.
    Schuch, Reinhold
    Stockholm University, Faculty of Science, Department of Physics.
    Spillmann, U.
    Tashenov, S.
    Trotsenko, S.
    Warczak, A.
    Weber, G.
    Wen, W.
    Winters, D. F. A.
    Winters, N.
    Yin, Z.
    Stoehlker, Th.
    Electron- and proton-impact excitation of heliumlike uranium in relativistic collisions2019In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 99, no 3, article id 032706Article in journal (Refereed)
    Abstract [en]

    We have studied the K-shell excitation of He-like uranium (U90+) in relativistic collisions with hydrogen and argon atoms. Performing measurements with different targets, as well as with different collision energies, enabled us to explore the proton- (nucleus-) impact excitation as well as the electron-impact excitation process for the heaviest He-like ion. The large fine-structure splitting in uranium allowed us to partially resolve excitation into different L-shell levels. State-of-the-art relativistic calculations which include excitation mechanisms due to the interaction with both protons (nucleus) and electrons are in good agreement with the experimental findings. Moreover, our experimental data clearly demonstrate the importance of including the generalized Breit interaction in the treatment of the electron-impact excitation process.

  • 10.
    Hannukainen, Julia
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Larson, Jonas
    Stockholm University, Faculty of Science, Department of Physics.
    Dissipation-driven quantum phase transitions and symmetry breaking2018In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 98, no 4, article id 042113Article in journal (Refereed)
    Abstract [en]

    By considering a solvable driven-dissipative quantum model, we demonstrate that continuous phase transitions in dissipative systems may occur without an accompanying symmetry breaking. As such, the underlying mechanism for this type of transition is qualitatively different from that of continuous equilibrium phase transitions. In our model, the transition is solely a result of the interplay between Hamiltonian and dissipative dynamics and manifests as a nonanalyticity in the steady state. (rho) over cap (ss) in the thermodynamic limit. Based on knowledge from critical classical models we suggest that this behavior derives from a rounding of a first-order phase transition into a continuous one due to large environment-induced fluctuations. Despite being conceptually different from the traditional continuous transitions, we show that expectations of local observables can still be characterized by a set of critical exponents.

  • 11.
    Kjellsson, Tor
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Førre, Morten
    Skjerlie Simonsen, Aleksander
    Selstø, Sølve
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Alternative gauge for the description of the light-matter interaction in a relativistic framework2017In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 96, no 2, article id 023426Article in journal (Refereed)
    Abstract [en]

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

  • 12.
    Kjellsson, Tor
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Selstø, Sølve
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Relativistic ionization dynamics for a hydrogen atom exposed to superintense XUV laser pulses2017In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 95, no 4, article id 043403Article in journal (Refereed)
    Abstract [en]

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

  • 13.
    Lindroth, Eva
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Dahlström, Jan Marcus
    Stockholm University, Faculty of Science, Department of Physics.
    Attosecond delays in laser-assisted photodetachment from closed-shell negative ions2017In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 96, no 1, article id 013420Article in journal (Refereed)
    Abstract [en]

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

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

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

  • 15.
    Mavrogordatos, Themistoklis K.
    Stockholm University, Faculty of Science, Department of Physics.
    Strong-coupling limit of the driven dissipative light-matter interaction2019In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 100, no 3, article id 033810Article in journal (Refereed)
    Abstract [en]

    We approach the strong-coupling thermodynamic limit in the response of the open driven Jaynes-Cummings (JC) oscillator. We do so by highlighting the role of quantum fluctuations against the semiclassical response in three distinct regimes of operation. We begin by demonstrating the persistence of photon blockade, predicted in Carmichael [Phys. Rev. X 5, 031028 (2015)], as a manifestation of the inherently quantum and nonlinear JC spectrum revealed for vanishing dissipation. We then proceed to discuss the importance of bistability, which, despite being present in photon blockades, is able to provide an alignment between the semiclassical nonlinearity and quantum dynamics only for a driving amplitude having the same order of magnitude as the light-matter coupling strength. This resolution brings us to the critical point of the well-known quantum-phase transition of second order on resonance, where the quantum and semiclassical pictures are once more contrasted for a varying participation of the two coherent interactions when going through the collapse of the quasienergy spectrum.

  • 16. Mezdari, Ferid
    et al.
    de Ruette, Nathalie
    Stockholm University, Faculty of Science, Department of Physics.
    Urbain, Xavier
    Spontaneous dissociation and rovibrational structure of the metastable D-2(-) anion2017In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 96, no 3, article id 032512Article in journal (Refereed)
    Abstract [en]

    Long-lived rovibrational states of the metastable D2-molecular anion, with lifetimes of the order of microseconds, were studied by recording the time-of-flight difference between D and D-fragments produced by spontaneous dissociation of the D2-complex. The simulated time-of-flight spectrum was adjusted to the experimental results, allowing us to extract the resonance energy relative to the dissociation threshold. A single value was found, 22.8 +/- 0.3 meV, which is somewhat larger than resonance energies predicted by theory for long-lived D2-rovibrational states with (J, v) quantum numbers (37,0), (37,1), and (38,0) [ Phys. Rev. A 75, 012507 (2007)]. This discrepancy seems due to the extreme sensitivity of thesemetastable states tominute features of the potential energy curve. The spectral feature is explained by the competition between autodetachment and spontaneous dissociation decay channels.

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

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

  • 18. Stråhlman, Christian
    et al.
    Moog, Bruno
    Ertan, Emelie
    Stockholm University, Faculty of Science, Department of Physics.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Kivimäki, Antti
    Richter, Robert
    Sankari, Rami
    Selective negative-ion formation from core-valence doubly excited states of the water molecule2018In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 98, no 5, article id 053432Article in journal (Refereed)
    Abstract [en]

    This study focuses on the role of negative-ion formation in the decay of core-valence doubly excited water molecules. Combining negative- and positive-ion coincidence measurements with calculated energies of core-valence doubly excited states, we find that O- and H- production is enhanced selectively. In particular, we suggest that O- production is correlated to double occupancy of the antibonding 4a(1) virtual orbital, while H- appears at electronic states with double occupancy in 2b(2). We also show that H- and O- can be created as a result of electron recapture close to the O 1s ionization potential.

  • 19.
    Tavakoli, Armin
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Université de Genève, Switzerland.
    Cabello, Adán
    Quantum predictions for an unmeasured system cannot be simulated with a finite-memory classical system2018In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 97, no 3, article id 032131Article in journal (Refereed)
    Abstract [en]

    We consider an ideal experiment in which unlimited nonprojective quantum measurements are sequentially performed on a system that is initially entangled with a distant one. At each step of the sequence, the measurements are randomly chosen between two. However, regardless of which measurement is chosen or which outcome is obtained, the quantum state of the pair always remains entangled. We show that the classical simulation of the reduced state of the distant system requires not only unlimited rounds of communication, but also that the distant system has infinite memory. Otherwise, a thermodynamical argument predicts heating at a distance. Our proposal can be used for experimentally ruling out nonlocal finite-memory classical models of quantum theory.

  • 20.
    Tuziemski, Jan
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Technical University of Gdańsk, Poland; National Quantum Information Center of Gdańsk, Poland.
    Lampo, Aniello
    Lewenstein, Maciej
    Korbicz, Jaroslaw K.
    Reexamination of the decoherence of spin registers2019In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 99, no 2, article id 022122Article in journal (Refereed)
    Abstract [en]

    We revisit the decoherence process of a multiqubit register interacting with a thermal bosonic bath. We generalize the previous studies by considering not only the register's behavior but also a part of its environment. In particular, we are interested in information flow from the register to the environment, which we describe using recently introduced multipartite quantum state structures called spectrum broadcast structures. Working in two specific cases of (i) two-qubit register and (ii) collective decoherence, we identify the regimes where the environment acquires almost complete information about the register state. We also study in more detail the interesting causal aspects related to the finite propagation time of the field disturbances between the qubits. Finally, we describe quantum state structures which appear due to the presence of protected spaces.

  • 21. Vaz da Cruz, Vinícius
    et al.
    Ertan, Emelie
    Stockholm University, Faculty of Science, Department of Physics.
    Ignatova, Nina
    Couto, Rafael C.
    Polyutov, Sergey
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Kimberg, Victor
    Gel'mukhanov, Faris
    Anomalous polarization dependence in vibrationally resolved resonant inelastic x-ray scattering of H2O2018In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 98, no 1, article id 012507Article in journal (Refereed)
    Abstract [en]

    It is well established that different electronic channels, in resonant inelastic x-ray scattering (RIXS), display different polarization dependences due to different orientations of their corresponding transition dipole moments in the molecular frame. However, this effect does not influence the vibrational progression in the Franck-Condon approximation. We have found that the transition dipole moments of core excitation and deexcitation experience ultrafast rotation during dissociation in the intermediate core-excited state. This rotation makes the vibrational progression in RIXS sensitive to the polarization of the x-ray photons. We study the water molecule, in which the effect is expressed in RIXS through the dissociative core-excited state where the vibrational scattering anisotropy is accompanied also by violation of parity selection rules for the vibrations.

1 - 21 of 21
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