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  • 51. Gelmukhanov, F
    et al.
    Privalov, Timofei
    KTH, Tidigare Institutioner                               , Kemi.
    Ågren, Hans
    KTH, Tidigare Institutioner                               , Kemi.
    Collapse of vibrational structure in spectra of resonant x-ray Raman scattering1997Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 56, nr 1, s. 256-264Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Extreme narrowing, or collapse, of electron-vibrational bands is predicted as a new phenomenon in resonant radiative and nonradiative x-ray scattering (RXS) spectra. It is shown that in the inelastic scattering case, that is, when the potential surfaces of ground and final slates are different, a considerable narrowing of the vibronic RXS band results from detuning the excitation Photon frequency omega away from the absorption resonance. By fine tuning the frequency, this may under special circumstances also occur in the region of strong photoabsorption. In the case of elastic Rayleigh scattering, that is, when the potential surfaces of ground and final states are identical, the narrowing results in a total collapse to a single resonance by detuning the frequency. The theory predicts how the differencies in vibrational structure of resonant and nonresonant photoemission spectra depends on the excitation frequency. The effect of frequency detuning on complex spectral multilevel structures due to multiplet: and spin-orbit splittings is discussed qualitatively. It is shown that the notion of: duration time for the x-ray scattering process plays a crucial role in the understanding of RXS spectra.

  • 52.
    Gel'mukhanov, Faris
    et al.
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Cronstrand, P.
    Ågren, Hans
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Resonant x-ray Raman scattering in a laser field2000Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 6102, nr 2Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A theory for laser-assisted resonant x-ray Raman scattering (RXS) is presented. The conditions for nonlinearity due to strong x-ray fields but without a laser field are first investigated, followed by studies of the consqeunces for the RXS cross section of having a weak x-ray field but strong laser fields resonant with different levels involved in the x-ray scattering. These levels are either connected with excitations of the ground state, with excitations between core excited states, or between unoccupied final states. When the final states are discrete, the RXS line is split by the applied laser field; when they are continuous the laser field induces autoionizationlike resonances in the RXS spectrum.

  • 53.
    Gelmukhanov, Faris
    et al.
    KTH, Tidigare Institutioner, Bioteknologi.
    Kimberg, Viktor
    KTH, Tidigare Institutioner, Bioteknologi.
    Ågren, Hans
    KTH, Tidigare Institutioner, Bioteknologi.
    Structure determination through measurements of Doppler-split Augerresonances in fixed-in-space molecules2004Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 69, nr 2, s. 020501(R)-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Auger resonances of dissociating atoms in randomly oriented molecules experience large electronic Dopplershifts. We predict that when fixed-in-space molecules are considered there will appear extra Doppler resonancesresulting from the diffractional scattering of the Auger electrons by the surrounding atoms. Theseresonances show sharp maxima in bond directions, something that makes them very promising as probes forlocal molecular structure using current energy- and angular-resolved electron-ion coincidence experiments.

  • 54.
    Gel'mukhanov, Faris
    et al.
    KTH, Tidigare Institutioner, Bioteknologi.
    Minkov, Ivaylo
    KTH, Tidigare Institutioner, Bioteknologi.
    Interchannel interference in resonant Auger scattering from fixed-in-space molecules as a technique for structure determination2004Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 70, nr 3, s. 032507-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A method for structure determination of polyatomic molecules with equivalent atoms is suggested. The method is based on an interference pattern in the resonant Auger scattering process. This pattern is caused by interference of resonant Auger channels corresponding to a core hole localized on different equivalent atoms. The predicted effect can be observed in angular resolved electron-ion coincidence measurements or, alternatively, using the ordinary Auger technique on surface-oriented molecules.

  • 55.
    Gel'mukhanov, Faris
    et al.
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Salek, Pawel
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Ågren, Hans
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Vibrationally resolved core-photoelectron spectroscopy as an infinite-slit interferometry2001Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 64, nr 1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    During a molecular vibration, an atom changes continuously its position. Just as the emitted photoelectron waves, the electromagnetic waves absorbed by the atom in the different positions are strictly coherent and have different well-defined phases. These phases depend on the relation between the instantaneous internuclear distance and the photoelectron, respectively, photon wavelengths. We predict that the interference of these coherent waves strongly influences the vibrational profile of the photoelectron spectra of core electrons in a molecule. This effect increases with increasing x-ray photon frequency and results in a deformation and broadening of the vibrational profile. In the case of surface adsorbed molecules, the vibrational profile depends strongly on the direction of the photoelectron ejection and photon momentum, and the orientational sensitivity of a vibrational profile can even be used as a tool to define the orientation of adsorbed molecules.

  • 56.
    Gel’mukhanov, Faris
    et al.
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Sałek, Paweł
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Privalov, Timofei
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Ågren, Hans
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Duration of x-ray Raman scattering1999Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 59, nr 1, s. 380-389Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    There has recently been much interest in using the notion of a duration time to analyze resonant x-ray Raman scattering (RXS) of atoms, molecules, and solids. This notion implies a selection of processes with different time scales responsible for the formation x-ray Raman spectra, and has been useful for actual predictions of various phenomena associated with RXS and that subsequently have been experimentally verified. However, the notion of a duration time for the x-ray scattering event can also have some paradoxical consequences, as when comparing the RXS duration with the relaxation time of the wave packet evolution in the case when the inverse detuning of the excitation energy is shorter than the time of flight or the lifetime of the core excited state. We present here a solution of this contradiction and give a detailed analysis of the notion of the duration time for RXS. It is shown that this time is complex and consists of two qualitatively different contributions. The first originates in the irreversible decay of the core excited state, while the imaginary part is caused by a reversible dephasing in the time domain. We investigate also the evolution of the wave packets of bound and dissociative states to stationary distributions. The theoretical analysis is accompanied by numerical examples of the time evolution of the wave packet in bound and dissociative core excited states of the N2 and HCl molecules.

  • 57.
    Gel'mukhanov, Faris
    et al.
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Ågren, Hans
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Salek, Pawel
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Doppler effects in resonant x-ray Raman scattering1998Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 57, nr 4, s. 2511-2526Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Theory for Doppler effects in resonant x-ray Raman scattering (RXS) is presented. It is shown that the "electron" Doppler effect is important in nonradiative RXS for decay transitions between continuum nuclear states lying above the dissociation threshold, and that the averaging of the RXS cross section over molecular orientations can lead to strong non-lorentzian broadenings of the atomiclike resonances. The Doppler effect is found to give a unique possibility to distinguish dissociating identical atoms, because different peaks correspond to atoms with opposite Doppler shifts. Spectral features of the atomiclike profile are predicted and analyzed. Strong oscillations of the RXS cross section will occur as a consequence of the interference of the Auger electrons. Due to the Doppler effect and the interference, the atomiclike profile can be associated with supernarrow spectral features, the width of which goes below the lifetime broadening and is practically independent of the spectral distribution of the incident radiation. As another consequence of the oscillations and strong anisotropy caused by the interference, we predict parity selection rules for Auger decay transitions in both bound and dissociative systems. The corresponding experiments can be realized by measurements of resonant Auger of surface adsorbed molecules and for molecules by the electron-ion coincidence technique.

  • 58. Ghiu, I.
    et al.
    Karlsson, Anders
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik.
    Broadcasting of entanglement at a distance using linear optics and telecloning of entanglement2005Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 72, nr 3Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We propose a scheme for broadcasting entanglement at a distance based on linear optics. We show that an initial polarization entangled state can be simultaneously split and transmitted to a pair of observers situated at different locations with the help of two conditional Bell-state analyzers based on two beam splitters characterized by the same reflectivity R. In particular for R=1/3 the final states coincide with the output states obtained by the broadcasting protocol proposed by Buzek [Phys. Rev. A 55, 3327 (1997)]. Further we present a different protocol called telecloning of entanglement, which combines the many-to-many teleportation and nonlocal optimal asymmetric cloning of an arbitrary entangled state. This scheme allows the optimal transmission of the two nonlocal optimal clones of an entangled state to two pairs of spatially separated receivers.

  • 59. Ghiu, Iulia
    et al.
    Bjoerk, Gunnar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik, Kvantelektronik och -optik, QEO.
    Marian, Paulina
    Marian, Tudor A.
    Probing light polarization with the quantum Chernoff bound2010Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 82, nr 2, s. 023803-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We recall the framework of a consistent quantum description of polarization of light. Accordingly, the degree of polarization of a two-mode state. (rho) over cap of the quantum radiation field can be defined as a distance of a related state (rho) over cap (b) to the convex set of all SU(2)-invariant two-mode states. We explore a distance-type polarization measure in terms of the quantum Chernoff bound and derive its explicit expression. A comparison between the Chernoff and Bures degrees of polarization leads to interesting conclusions for some particular states chosen as illustrative examples.

  • 60. Grünwald, P.
    et al.
    Vasylyev, D.
    Häggblad, Jon
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Numerisk analys, NA.
    Vogel, W.
    Quantum measurement of broadband nonclassical light fields2015Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 91, nr 1, s. 013816-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Based on the measurement of quantum correlation functions, the quantum statistical properties of spectral measurements are studied for broadband radiation fields. The spectral filtering of light before its detection is compared with the direct detection followed by the spectral analysis of the recorded photocurrents. As an example, the squeezing spectra of the atomic resonance fluorescence are studied for both types of filtering procedures. The conditions for which the detection of the nonclassical signatures of the radiation is possible are analyzed. For the considered example, photocurrent filtering appears to be the superior option to detect nonclassicality due to the vacuum-noise effects in the optical filtering.

  • 61.
    Guimaraes, Freddy Fernandes
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Kimberg, Victor
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Felicissimo, Viviane C.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Gelmukhanov, Faris
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Cesar, A.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Infrared–x-ray pump-probe spectroscopy of the NO molecule2005Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 72, nr 1, artikkel-id 012714Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Two color infrared-x-ray pump-probe spectroscopy of the NO molecule is studied theoretically and numerically in order to obtain a deeper insight of the underlying physics and of the potential of this suggested technology. From the theoretical investigation a number of conclusions could be drawn: It is found that the phase of the infrared field strongly influences the trajectory of the nuclear wave packet, and hence, the x-ray spectrum. The trajectory experiences fast oscillations with the vibrational frequency with a modulation due to the anharmonicity of the potential. The dependences of the x-ray spectra on the delay time, the duration, and the shape of the pulses are studied in detail. It is shown that the x-ray spectrum keep memory about the infrared phase after the pump field left the system. This memory effect is sensitive to the time of switching-off the pump field and the Rabi frequency. The phase effect takes maximum value when the duration of the x-ray pulse is one-fourth of the infrared field period, and can be enhanced by a proper control of the duration and intensity of the pump pulse. The manifestation of the phase is different for oriented and disordered molecules and depends strongly on the intensity of the pump radiation.

  • 62.
    Guimaraes, Freddy Fernandes
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Kimberg, Victor
    KTH, Skolan för bioteknologi (BIO).
    Felicissimo, Viviane C.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Gel'mukhanov, Faris
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Cesar, A.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Phase sensitive x-ray absorption driven by strong infrared fields2005Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 71, nr 4, artikkel-id 043407Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper it is demonstrated that electron vibrational absorption of molecules driven by strong IR field provides rich physical interpretations of dynamical processes on a short time scale. The phase of an infrared field influences strongly the trajectory of the nuclear wave packet and the probing spectrum. It is shown that the probe spectrum keeps memory of the infrared phase even after that the pump field left the system. The phase effect takes maximum value when the duration of the probe pulse is of the order of the infrared field period, and can be enhanced by a proper control of the duration and intensity of the pump pulse. The phase effect is different for oriented and disordered molecules and depends strongly on the intensity of pump radiation. It can be an effective tool to study charge transfer processes like proton transfer in hydrogen bonded networks.

  • 63. Gurell, J.
    et al.
    Biemont, E.
    Blagoev, K.
    Fivet, V.
    Lundin, P.
    Mannervik, S.
    Norlin, Lars-Olov
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Quinet, P.
    Rostohar, D.
    Royen, P.
    Schef, P.
    Laser-probing measurements and calculations of lifetimes of the 5d D-2(3/2) and 5d D-2(5/2) metastable levels in BaII2007Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 75, nr 5, s. 052506-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The two metastable levels 5d(2)D(3/2) and 5d(2) D-5/2 in Ba II both show extremely long lifetimes of the order of several tens of seconds each. This has been found both by experiments and by theoretical predictions. The small transition probabilities associated with these two levels make them interesting and challenging for theoreticians as well as for experimentalists. Several calculations and measurements of these two lifetimes have been made previously but discrepancies between the results are present. This article presents values of ??? = 89.4 +/- 15.6 s for the D-2(3/2) level and ??? = 32.0 +/- 4.6 s for the D-2(5/2) level measured in a beam-laser experiment performed at the ion storage ring CRYRING. These values are supported by our new calculations resulting in ???= 82.0 s for the D-2(3/2) level and ???= 31.6 s for the D-2(5/2) level.

  • 64. Hakkarainen, Timo
    et al.
    Setala, Tero
    Friberg, Ari T.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Electromagnetic near-field interactions of a dipolar emitter with metal and metamaterial nanoslabs2011Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 84, nr 3, s. 033849-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate the emission properties of a polarizable point dipole placed within a subwavelength distance from a silver or a slightly absorbing, negative-index metamaterial nanoslab. Using electromagnetic theory we show that in the immediate vicinity of the slab the dipole-slab interaction prevents the dipole from radiating. For the metamaterial slab close to the perfect-lens arrangement, the interaction is relatively weak and of short range. In particular, a region exists in the near zone of the metamaterial slab where the dipole emission is not disturbed by the interaction, and a bright intensity distribution of subwavelength width is created on the opposite side of the slab. This suggests that a low-loss metamaterial slab can act as a near-field imaging device which does not disturb the object. For the silver slab the interaction is stronger and it reaches over the near-field zone, adversely influencing the imaging capabilities in terms of brightness and resolution. The results are important for the development of metal and metamaterial superlenses.

  • 65.
    Hao, Jiaming
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Ren, Qijun
    An, Zhenghua
    Huang, Xueqin
    Chen, Zhanghai
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Zhou, Lei
    Optical metamaterial for polarization control2009Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 80, nr 2Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present the design, characterization, and modeling of a specific optical metamaterial, and employ it to manipulate the light polarizations at optical frequencies. Experimental results reveal that the maximum polarization conversion efficiency, i.e., the energy portion converted from s to p polarization after reflection, can be as high as 96% at the wavelength of similar to 685 nm. Simulations and analytical results, which are in reasonable agreements with the experimental results, reveal that the underlying physics are governed by the particular electric and magnetic resonances in the optical metamaterial.

  • 66. He, Guang S.
    et al.
    Qin, Hai-Yan
    Zheng, Qingdong
    Prasad, Paras N.
    Jockusch, Steffen
    Turro, Nicholas J.
    Halim, Marlin
    Sames, Dalibor
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Dynamic properties and optical phase conjugation of two-photon pumped ultrashort blue stimulated emission in a chromophore solution2008Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 77, nr 1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dynamic properties of two-photon pumped blue lasing (similar to 470 nm) in the solution of an organic chromophore [2-acetyl-6-(dimethylamino)naphthalene], excited by similar to 160-fs laser pulses at similar to 775 nm, have been studied. Both the forward and backward stimulated emission are enhanced by feedback from the reflection at the two optical windows of the solution filled cuvette. Under current experimental conditions, the lasing wavelengths in the forward and backward directions were almost the same, but both blueshifted compared to the fluorescence peak wavelength of the sample solution. The temporal behavior of the lasing output was recorded by a high-speed streak camera system. The multipulse structure and spectral properties of the output lasing are semiquantitatively explained. In addition, excellent optical phase-conjugation properties of the backward stimulated emission were observed; the aberration influences from an aberrator on the backward lasing beam were automatically removed.

  • 67.
    Hennies, F.
    et al.
    Institut für Experimentalphysik, Universität Hamburg.
    Polyutov, Sergey
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Minkov, Ivaylo
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Pietzsch, A.
    Institut für Experimentalphysik, Universität Hamburg.
    Nagasono, M.
    Institut für Experimentalphysik, Universität Hamburg.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Triguero, L.
    Piancastelli, M. N.
    Department of Physics, Uppsala University.
    Wurth, W.
    Institut für Experimentalphysik, Universität Hamburg.
    Gel'mukhanov, Faris
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Föhlisch, A.
    Institut für Experimentalphysik, Universität Hamburg.
    Dynamic interpretation of resonant x-ray Raman scattering: ethylene and benzene2007Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 76, nr 3, s. 032505-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a dynamic interpretation of resonant x-ray Raman scattering where vibrationally selective excitation into molecular resonances has been employed in comparison with excitation into higher lying continuum states for condensed ethylene and benzene as molecular model systems. In order to describe the purely vibrational spectral loss features and coupled electronic and vibrational losses the one-step theory for resonant soft x-ray scattering is applied, taking multiple vibrational modes and vibronic coupling into account. The scattering profile is found to be strongly excitation energy dependent and to reflect the intermediate states dynamics of the scattering process. In particular, the purely vibrational loss features allow one to map the electronic ground state potential energy surface in light of the excited state dynamics. Our study of ethylene and benzene underlines the necessity of an explicit description of the coupled electronic and vibrational loss features for the assignment of spectral features observed in resonant x-ray Raman scattering at polyatomic systems, which can be done in both a time independent and a time dependent picture. The possibility to probe ground state vibrational properties opens a perspective to future applications of this photon-in-photon-out spectroscopy.

  • 68. Heydari, H.
    et al.
    Björk, Gunnar
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Sanchez-Soto, L. L.
    Measurable entanglement criterion for two qubits2003Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 68, nr 6Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We propose a directly measurable criterion for the entanglement of two qubits. We compare the criterion with other criteria, and we find that for pure states, and some mixed states, it coincides with the state's concurrence. The measure can be obtained with a Bell-state analyzer and the ability to make general local unitary transformations. However, the procedure fails to measure the entanglement of a general mixed two-qubit state.

  • 69. Jackson, A D
    et al.
    Kavoulakis, G M
    Lundh, Emil
    KTH, Tidigare Institutioner, Fysik.
    Phase diagram of a rotating Bose-Einstein condensate with anharmonic confinement2004Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 69, nr 5, s. 053619-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We examine the phase diagram of an effectively repulsive Bose-Einstein condensate of atoms that rotates in a quadratic-plus-quartic potential. With use of a variational method we identify the three possible phases of the system as a function of the rotational frequency of the trap and of the coupling constant. The derived phase diagram is shown to be universal and partly exact in the limit of weak interactions and small anharmonicity. The variational results are found to be consistent with numerical solutions of the Gross-Pitaevskii equation.

  • 70. Jackson, A D
    et al.
    Kavoulakis, G M
    Lundh, Emil
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Stability of the solutions of the Gross-Pitaevskii equation2005Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 72, nr 5, s. 053617-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We examine the static and dynamic stability of the solutions of the Gross-Pitaevskii equation and demonstrate the intimate connection between them. All salient features related to dynamic stability are reflected systematically in static properties. We find, for example, the obvious result that static stability always implies dynamic stability and present a simple explanation of the fact that dynamic stability can exist even in the presence of static instability.

  • 71.
    Jakob, Matthias
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Stenholm, Stig
    KTH, Tidigare Institutioner, Fysik.
    Effects of a thermal reservoir on variational functions in open systems2004Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 70, nr 1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We connect the theory of a Lyapunov functional for an open system with the thermophysical concept of the relative entropy or equivalently with the entropy production rate. In order to do this we consider the environment of the open system as a thermal reservoir, which introduces the temperature as a thermophysical quantity. The general theory of the Lyapunov functional of an open system constructs a metric operator which contains an element of ambiguity in its scaling. This ambiguity can be removed by assuming a thermostatistic environment which fixes the scaling of the metric operator in a unique manner. The Lyapunov functional thus acquires a thermophysical meaning and can be connected with a relative entropy. In this case the metric operator is related to the inverse of the stationary density operator of the system. We illustrate the theory on a two-level atomic system and a degenerate three-level atom which are exposed to a thermal electromagnetic environment.

  • 72.
    Jakob, Matthias
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Stenholm, Stig
    KTH, Tidigare Institutioner, Fysik.
    Variational functions in degenerate open quantum systems2004Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 69, nr 4, s. 042105-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have derived a Lyapunov functional for a degenerate open atomic system. This functional develops monotonically towards its stationary state. The open system is described by a Lindblad-type master equation. For the construction of the variational functional it is necessary that the Lindblad operator can be diagonalized. Since the generator of motion is non-Hermitian, diagonalization is, in general, only possible if the eigenvalues are nondegenerate. In this paper, we propose that in a physical system the biorthogonal eigenbasis of the Lindblad operator remains complete even when degeneracy is present. Thus diagonalization of the Lindblad operator, and consequently the construction of the variational functional, is still possible. We discuss the reasons and illustrate the theory of the variational functional for a driven Lambda-type three-level atom with degenerate ground state. The degeneracy has interesting effects on the variational functional in the steady state with respect to its interpretation as an entropic quantity. In case of the driven three-level atom, the dark state turns out to be an isentropic state.

  • 73. Jansik, B.
    et al.
    Schimmelpfennig, B.
    Ågren, Hans
    KTH, Tidigare Institutioner                               , Bioteknologi.
    Relativistic study of vuv radiation properties from Kr-Xe gas mixtures2003Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 67, nr 4Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In an effort to obtain a microscopic understanding of the origin of vuv emission from inert heavy-atom gas mixtures we present results from relativistic calculations of the krypton-xenon spectrum in the 68 000 cm(-1) region. Calculations carried out on the interatomic interaction in the ground and in the low-lying spin-orbit excited states [0(-)(P-3(2)), 0(+)(P-3(1)), 1(P-3(1)), 1(P-3(2)), 2(P-3(1))] of the krypton-xenon dimer are presented. The calculations were executed in a two-step procedure in which the CCSD(T) model for the ground state and the CCSD response theory model for the excited states were used to obtain spin-free potential curves in the first step. A perturbational treatment of the spin-orbit interaction within the atomic mean-field approximation was applied in the next step. Large-core quasirelativistic effective core potentials with richly augmented valence basis sets and midbond functions were used. All calculations were corrected for basis set superposition errors by applying the counterpoise method. For all involved states, spin-orbit perturbed potential energy curves were computed and equilibrium geometries, potential well depths, and local extrema were determined. Vibrational analysis and Franck-Condon factors for the ground and 0(+)(P-3(1)),1(P-3(1)) states were also calculated. The geometry dependence of the electronic dipole transition matrix elements between all involved excited states and the ground state was investigated. Excitation energies and potentials were obtained that are in excellent agreement with results based on fitting to experimental data. Out of some earlier disparate experimental assignments of the character of the excited states of the KrXe complex, the present results adhere most closely to the ones presented by Pibel [J. Chem. Phys. 101, 10 242 (1994)]. Analyzed together with the experimental data, the theoretical results provide a clear picture of the organization of exciplex states and of the origin of strong vuv emission from these states that follows from binary collisions of the heavy inert Kr and Xe atoms.

  • 74. Jiemchooroj, A.
    et al.
    Sernelius, B. E.
    Norman, P.
    C6 dipole-dipole dispersion coefficients for the n-alkanes: Test of an additivity procedure2004Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 69, nr 4, s. 044701-1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dipole-dipole dispersion coefficients for pairs of n-alkane molecules with six or less carbon atoms were studied. The calculations were based on the dynamic polarizabilities of the molecules on the imaginary frequency axis. The dynamic polarizabilities in turn were obtained from Kohn-Sham density-functional theory polarization propagator calculations using the hybrid B3LYP exchange-correlation functional. The results for the static polarizabilities of each molecule were decomposed into bond polarizabilities and values for the polarizabilities of the C-H and C-C bonds.

  • 75. Johansson, Markus
    et al.
    Sjöqvist, Erik
    Andersson, L. Mauritz
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvantelektronik och -optik, QEO.
    Ericsson, Marie
    Hessmo, Bjoern
    Singh, Kuldip
    Tong, D. M.
    Robustness of nonadiabatic holonomic gates2012Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 86, nr 6, s. 062322-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The robustness to different sources of error of the scheme for nonadiabatic holonomic gates proposed previously [New J. Phys. 14, 103035 (2012)] is investigated. Open system effects as well as errors in the driving fields are considered. It is found that the gates can be made error resilient by using sufficiently short pulses. The principal limit of how short the pulses can be made is given by the breakdown of the quasi-monochromatic approximation. A comparison with the resilience of adiabatic gates is carried out.

  • 76. Kalhori, S.
    et al.
    Thomas, R.
    Al-Khalili, A.
    Ehlerding, A.
    Hellberg, F.
    Neau, A.
    Larsson, M.
    Larson, Åsa
    KTH, Tidigare Institutioner, Fysik.
    Huneycutt, A. J.
    McCall, B. J.
    Djuric, N.
    Dunn, G. H.
    Semaniak, J.
    Novotny, O.
    Paal, A.
    Österdahl, F.
    Orel, A. E.
    Resonant ion-pair formation in electron collisions with rovibrationally cold H-3(+)2004Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 69, nr 2, s. 022713-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Experimental and theoretical cross sections for the resonant ion-pair formation (RIP) in electron collisions with rovibrationally cold H-3(+) ions are presented. Absolute cross sections for the RIP process producing H- ions are measured for center-of-mass energies between 2-20 eV using the CRYRING, heavy-ion storage ring. Theoretical cross sections are obtained using wave-packet propagation on both one- and two-dimensional models of relevant diabatic-potential energy surfaces and couplings of H-3(+) and H-3.

  • 77. Karawajczyk, A.
    et al.
    Erman, P.
    Rachlew-Källne, Elisabeth
    KTH, Tidigare Institutioner                               , Fysik.
    Riu, J. R. I.
    Stankiewicz, M.
    Franzen, K. Y.
    Veseth, L.
    Neutral fragmentation of superexcited oxygen molecules2000Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 61, nr 3, s. art. no.-32718Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The mechanisms of neutral dissociation of oxygen molecules in the excitation energy range 15-25 eV have been studied in a dispersed fluorescence experiment. By detecting the fluorescence from excited oxygen atoms, we find that neutral superexcited O-2 states below 20 eV dissociate into O(g.s.) + O(3s,3p). At higher excitation energies (h nu = 20-25 eV) the curve-crossing interactions following excitations to members of the Rydberg c (4)Sigma(u)(-) series also yield atoms in Rydberg states (nl,n greater than or equal to 4). The experimental data are analyzed on the ground of many-body perturbation theory, calculations which indicate the structure of the predissociating states converging to the experimentally observed ones.

  • 78. Kimberg, Victor
    et al.
    Gejo, Tatsuo
    Oura, Masaki
    Tokushima, Takashi
    Horikawa, Yuka
    Arai, Hidemi
    Shin, Shik
    Kosugi, Nobuhiro
    Rydberg-valence mixing and interchannel coupling in resonant oxygen 1s inelastic x-ray scattering of O_22012Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 85, nr 3Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Rydberg-valence (RV) mixing and doublet-quartet (DQ) interchannel coupling in the core-excited states of triplet open-shell O2 are experimentally and theoretically unveiled through the resonant inelastic x-ray scattering around the O 1s→σ∗u resonance. Ab initio calculations explain complicated excitation energy dependence of the spectral profile by the interplay of the DQ interchannel coupling under the presence of the RV mixing. Complicated intermediate states with valence and/or Rydberg character are successfully analyzed through the filtering of pure valence and pure Rydberg final states.

  • 79.
    Kimberg, Victor
    et al.
    KTH, Skolan för bioteknologi (BIO).
    Guimaraes, Freddy Fernandes
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Felicissimo, Viviane C.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Gel'mukhanov, Faris
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Phase-sensitive wave-packet dynamics caused by a breakdown of the rotating-wave approximation2006Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 73, nr 2, artikkel-id 023409Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The water dimer driven by strong infrared field is studied in the two-vibrational mode approximation. A pump pulse excites the OH vibrational modes and creates a coherent superposition of vibrational states of the low-frequency OO mode. The solution of the Schrodinger equation in the adiabatic approximation shows a strong sensitivity of the OO vibrational wave-packet dynamics to the absolute phase of the pump field. This effect appears due to a break down of the rotating-wave approximation when the Rabi frequency of the OH vibrational transition approaches the frequency of the OH mode. The violation of the rotating wave approximation modifies considerably the interaction of the probe radiation with the laser-driven molecule.

  • 80.
    Kimberg, Victor
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Polyutov, Sergey
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Gel'mukhanov, Faris
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Baev, Alexander
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Zheng, Q.D.
    Institute for Lasers, Photonics and Biophotonics, State University of New York at Buffalo.
    He, G. S.
    Institute for Lasers, Photonics and Biophotonics, State University of New York at Buffalo.
    Dynamics of cavityless lasing generated by ultrafast multiphoton excitation2006Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 74, nr 3, artikkel-id 033814Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A dynamical theory is developed with the purpose of explaining recent experimental results on multiphoton-excited amplified stimulated emission (ASE). Several conspicuous features of this experiment are analyzed, like the threshold dependence of the spectral profile on the pump intensity, and spectral shifts of the ASE pulses co- and counterpropagating relative to the pump pulse. Two models are proposed and evaluated, one based on the isolated molecule and another which involves solvent interaction. The spectral shift between the forward and backward ASE pulses arises in the first model through the competition between the ASE transitions from the pumped vibrational levels and from the bottom of the excited-state well, while in the solvent-related model the dynamical solute-solvent interaction leads to a relaxed excited state, producing an additional ASE channel. In the latter model the additional redshifted ASE channel makes the dynamics of ASE essentially different from that in the molecular model because the formation of the relaxed state takes a longer time. The variation of the pump intensity influences strongly the relative intensities of the different ASE channels and, hence, the spectral shape of ASE in both models. The regime of ASE changes character when the pump intensity crosses a threshold value. Such a phase transition occurs when the ASE rate approaches the rate of vibrational relaxation or the rate of solute-solvent relaxation in the first excited state.

  • 81. Kivimäki, A.
    et al.
    de Simone, M.
    Coreno, M.
    Feyer, V.
    Garcia, Emilio Melero
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Atom- och molekylfysik.
    Ruiz, Jesús Alvarez
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Atom- och molekylfysik.
    Richter, R.
    Prince, K. C.
    Observation of core-hole double excitations in water using fluorescence spectroscopy2007Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 75, nr 1, s. 014503-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The hydrogen Lyman-alpha, Balmer-alpha, and Balmer-beta emission has been measured from the H2O molecule at photon energies exceeding the 1s ionization threshold. Fluorescence emission is shown to be a sensitive probe to neutral core-hole doubly excited states and singly ionized 1s shake-up states that are embedded in the core ionization continuum. In addition, the photoabsorption spectrum of the water molecule in the energy range of the double excitations has been measured with better statistics than previously.

  • 82. Kivimäki, A.
    et al.
    Norman, P.
    Coreno, M.
    De Simone, M.
    Grazioli, C.
    Totani, R.
    Ressel, B.
    Ottosson, H.
    Puglia, C.
    Use of two-dimensional photoelectron spectroscopy in the decomposition of an inner-shell excitation spectrum broadened by super-Coster-Kronig decay2013Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 88, nr 6, artikkel-id 062502Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Ge 3p core excitation spectrum of the n-butylgermane molecule only reveals two peaks, whereas the rest of the fine structure is obscured due to the large lifetime broadenings of core-excited states. A two-dimensional presentation of resonant photoemission spectra allows us to observe some other resonances. The interpretation of experimental results is supported by ab initio calculations conducted at the four-component relativistic level of theory with full account made for spin-orbit interactions already in the zeroth-order Hamiltonian. © 2013 American Physical Society.

  • 83. Klimov, A. B.
    et al.
    Björk, Gunnar
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvantelektronik och -optik, QEO.
    Sanchez-Soto, L. L.
    Optimal quantum tomography of permutationally invariant qubits2013Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 87, nr 1, s. 012109-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Mutually unbiased bases determine an optimal set of measurements to extract complete information about the quantum state of a system. However, quite often a priori information about the state exists, making some of the measurement bases superfluous. This is, for example, the case when multiqubit states belong to the permutationally invariant subspace. In this paper we derive the minimal sets of mutually unbiased bases needed to tomographically reconstruct such states.

  • 84. Klimov, A. B.
    et al.
    Sanchez-Soto, L. L.
    Yustas, E. C.
    Soderholm, J.
    Björk, Gunnar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Distance-based degrees of polarization for a quantum field2005Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 72, nr 3Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It is well established that unpolarized light is invariant with respect to any SU(2) polarization transformation. This requirement fully characterizes the set of density matrices representing unpolarized states. We introduce the degree of polarization of a quantum state as its distance to the set of unpolarized states. We use two different candidates of distance, namely the Hilbert-Schmidt and the Bures metric, showing that they induce fundamentally different degrees of polarization. We apply these notions to relevant field states and we demonstrate that they avoid some of the problems arising with the classical definition.

  • 85.
    Kothe, Christian
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Björk, Gunnar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Entanglement quantification through local observable correlations2007Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 75, nr 1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a significantly improved scheme of entanglement detection inspired by local uncertainty relations for a system consisting of two qubits. Developing the underlying idea of local uncertainty relations, namely correlations, we demonstrate that it is possible to define a measure which is invariant under local unitary transformations and which is based only on local measurements. It is quite simple to implement experimentally and it allows entanglement quantification in a certain range for mixed states and exactly for pure states, without first obtaining full knowledge (e.g., through tomography) of the state.

  • 86.
    Kothe, Christian
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik, Kvantelektronik och -optik, QEO.
    Björk, Gunnar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik, Kvantelektronik och -optik, QEO.
    Bourennane, Mohamed
    Arbitrarily high super-resolving phase measurements at telecommunication wavelengths2010Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 81, nr 6, s. 063836-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present two experiments that achieve phase super-resolution at telecommunication wavelengths. One of the experiments is realized in the space domain and the other is realized in the time domain. Both experiments show high visibility and are performed with standard lasers and single-photon detectors. The first experiment uses six-photon coincidences, whereas the latter experiment needs no coincidence measurements, is easy to perform, and achieves, in principle, arbitrarily high phase super-resolution. Here, we demonstrate a 30-fold increase of the resolution. We stress that neither entanglement nor joint detection is needed in these experiments, which demonstrates that neither is necessary to achieve phase super-resolution.

  • 87. Kothe, Christian
    et al.
    Madsen, Lars Skovgaard
    Andersen, Ulrik Lund
    Björk, Gunnar
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvantelektronik och -optik, QEO.
    Experimental determination of the degree of polarization of quantum states2013Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 87, nr 4, s. 043814-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We demonstrate experimental excitation-manifold-resolved polarization characterization of quantum states of light ranging from the few-photon to the many-photon level. In contrast to the traditional characterization of polarization that is based on the Stokes parameters, we experimentally determine the Stokes vector of each excitation manifold separately. Only for states with a given photon number do the methods coincide. For states with an indeterminate photon number, for example Gaussian states, the employed method gives a richer and more accurate description. We apply the method both in theory and in experiment to some common states to demonstrate its advantages.

  • 88. Kovtun, Oleksiy
    et al.
    Tioukine, Valeri
    Surzhykov, Andrey
    Yerokhin, Vladimir A.
    Cederwall, Bo
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
    Tashenov, Stanislav
    Spin-orbit interaction in bremsstrahlung and its effect on the electron motion in a strong Coulomb field2015Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 92, nr 6, artikkel-id 062707Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Linear polarization of bremsstrahlung x rays produced in collisions of longitudinally polarized 2.1-MeV electrons with gold atoms was studied using the Compton scattering technique. We observed that the angle of x-ray polarization is strongly correlated with the incoming electron polarization. This correlation reveals the dominance of the spin-orbit interaction in bremsstrahlung and indicates a striking effect of the electron spin on the electron motion in a strong Coulomb field. The results confirm the validity of the theoretical predictions in a computationally challenging energy regime.

  • 89. Kragset, S.
    et al.
    Babaev, Egor
    Sudbo, A.
    Effects of boundaries and density inhomogeneity on states of vortex matter in Bose-Einstein condensates at finite temperature2008Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 77, nr 4Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Most of the literature on quantum vortices predicting various states of vortex matter in three dimensions at finite temperatures in quantum fluids is based on the assumption of an extended and homogeneous system. This is well known not to be the case in actual Bose-Einstein condensates in traps, which are finite systems with nonuniform density. This raises the question to what extent one can speak of different aggregate states of vortex matter (vortex lattices, liquids, and tensionless vortex tangles) in these systems. To address this point, in the present work we focus on the finite-size, boundaries and density inhomogeneity effects on thermal vortex matter in a Bose-Einstein condensate. To this end we perform Monte Carlo simulations on a model system describing trapped Bose-Einstein condensates. Throughout the paper, we draw on analogies with results for vortex matter obtained for extended systems. We also consider, for comparison, the cylindrical confinement geometry with uniform density profile from the center out to the edge of the trap. The trapping potential is taken to be generically of an anharmonic form in such a way as to interpolate between a harmonic trap and a cylindrical confinement geometry. It also allows for a dip in the density profile at the center. We find distinct thermal equilibrium properties of the vortex system as the qualitative characteristics of the trapping potential are varied. For a uniform cylindrical confinement geometry, we find a vortex lattice at the center of the trap as well as ringlike thermal fluctuations of the vortex system as the trap edge is approached. For a harmonic trap, we find a distinct region at the edge of the trap where the vortex lines appear to have lost their line tension. Due to the steep density gradient, this crosses directly over to a vortex-line lattice at the center of the trap at low temperatures. At higher temperatures, an intermediate tensionful vortex liquid may exist. For an anharmonic trap where the ground state condensate density features a local minimum at the center of the trap, we find a corresponding region which appears to feature a tensionless vortex-line liquid phase. This work suggests that, finiteness and intrinsic inhomogeneity of the system notwithstanding, one nonetheless can approximately invoke the notion of distinct aggregate states of vortex matter realized at certain length scales. This might be helpful, in particular, in the search for possible new states of vortex matter in Bose-Einstein condensates with multiple components and different symmetries.

  • 90. Krueger, P.
    et al.
    Andersson, L. Mauritz
    Wildermuth, S.
    Hofferberth, S.
    Haller, E.
    Aigner, S.
    Groth, S.
    Bar-Joseph, I.
    Schmiedmayer, J.
    Potential roughness near lithographically fabricated atom chips2007Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 76, nr 6Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Potential roughness has been reported to severely impair experiments in magnetic microtraps. We show that these obstacles can be overcome as we measure disorder potentials that are reduced by two orders of magnitude near lithographically patterned high-quality gold layers on semiconductor atom chip substrates. The spectrum of the remaining field variations exhibits a favorable scaling. A detailed analysis of the magnetic field roughness of a 100-mu m-wide wire shows that these potentials stem from minute variations of the current flow caused by local properties of the wire rather than merely from rough edges. A technique for further reduction of potential roughness by several orders of magnitude based on time-orbiting magnetic fields is outlined.

  • 91. Kukk, E.
    et al.
    Ha, D. T.
    Wang, Y.
    Piekarski, D. G.
    Diaz-Tendero, S.
    Kooser, K.
    Itala, E.
    Levola, H.
    Alcami, M.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Atom- och molekylfysik.
    Martin, F.
    Internal energy dependence in x-ray-induced molecular fragmentation: An experimental and theoretical study of thiophene2015Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 91, nr 4, artikkel-id 043417Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A detailed experimental and theoretical investigation of the dynamics leading to fragmentation of doubly ionized molecular thiophene is presented. Dissociation of double-ionized molecules was induced by S 2p core photoionization and the ionic fragments were detected in coincidence with Auger electrons from the core-hole decay. Rich molecular dynamics was observed in electron-ion-ion coincidence maps exhibiting ring breaks accompanied by hydrogen losses and/or migration. The probabilities of various dissociation channels were seen to be very sensitive to the internal energy of the molecule. Theoretical simulations were performed by using the semiempirical self-consistent charge-density-functional tight-binding method. By running thousands of these simulations, the initial conditions encountered in the experiment were properly taken into account, including the systematic dependencies on the internal (thermal) energy. This systematic approach, not affordable with first-principle methods, provides a good overall description of the complex molecular dynamics observed in the experiment and shows good promise for applicability to larger molecules or clusters, thus opening the door to systematic investigations of complex dynamical processes occurring in radiation damage.

  • 92. Kukk, E.
    et al.
    Riu, J. R. I.
    Stankiewicz, M.
    Hatherly, P. A.
    Erman, P.
    Rachlew, Elisabeth
    KTH, Tidigare Institutioner                               , Fysik.
    Winiarczyk, P.
    Huttula, M.
    Aksela, S.
    Dissociation of deuteromethane following carbon 1s core ionization2002Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 66, nr 1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Energy-resolved electron-ion coincidence spectra of the deuteromethane molecule were measured following ionization by narrow-band synchrotron radiation. The ion mass spectra were recorded in coincidence with the outer and inner valence photoelectrons and with the normal Auger electrons from the decay of the carbon 1s core hole. Complementary noncoincidence ion mass spectra were measured below and above the C 1s threshold. The fragmentation patterns of the singly and doubly ionized deuteromethane under different ionization conditions are examined. Carbon core ionization is shown to open new photodissociation pathways not available in the valence ionization photon energy regime. With the aid of ab initio quantum chemistry calculations, a two-step model of the dissociation following core ionization is proposed, showing a good agreement with the experimental findings.

  • 93. Kvaal, Simen
    et al.
    Jarlebring, Elias
    Departement Computerwetenschappen, Katholieke Universiteit Leuven.
    Michiels, Wim
    Computing singularities of perturbation series2011Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 83, nr 3, s. 032505-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Many properties of current ab initio approaches to the quantum many-body problem, both perturbational and otherwise, are related to the singularity structure of the Rayleigh-Schrodinger perturbation series. A numerical procedure is presented that in principle computes the complete set of singularities, including the dominant singularity which limits the radius of convergence. The method approximates the singularities as eigenvalues of a certain generalized eigenvalue equation which is solved using iterative techniques. It relies on computation of the action of the Hamiltonian matrix on a vector and does not rely on the terms in the perturbation series. The method can be useful for studying perturbation series of typical systems of moderate size, for fundamental development of resummation schemes, and for understanding the structure of singularities for typical systems. Some illustrative model problems are studied, including a helium-like model with delta-function interactions for which Moller-Plesset perturbation theory is considered and the radius of convergence found.

  • 94.
    Laestadius, Andre
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.).
    Benedicks, Michael
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.).
    Non-existence of a Hohenberg-Kohn Variational Principle in Total Current Density Functional Theory2015Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 91, nr 3, artikkel-id 032508Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    For a many-electron system, whether the particle density rho and the total current density j are sufficient to determine the one-body potential V and vector potential A, is still an open question. For the one-electron case, a Hohenberg-Kohn theorem exists formulated with the total current density. Here we show that the generalized Hohenberg-Kohn energy functional E_{V_0,A_0}(rho,j) = <psi(rho,j),H(V_0,\A_0)psi(rho,j)> can be minimal for densities that are not the ground-state densities of the fixed potentials V_0 and A_0. Furthermore, for an arbitrary number of electrons and under the assumption that a Hohenberg-Kohn theorem exists formulated with rho and j, we show that a variational principle for Total Current Density Functional Theory as that of Hohenberg-Kohn for Density Functional Theory does not exist. The reason is that the assumed map from densities to the vector potential, written (rho,j) -> A(rho,j;x), enters explicitly in E_{V_0,A_0}(rho,j).

  • 95.
    Laghaout, Amine
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik.
    Björk, Gunnar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Feasibility of Bell tests with the W state2010Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 81, nr 3Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The feasibility of Bell tests depends to a large extent on the tradeoff of difficulty between the preparation and the measurement of entangled systems. Polarization-entangled systems, though easy to measure, pose a relative challenge in their preparation. The opposite holds with entangled energy eigenstates for which the preparation is relatively straightforward. A way to perform measurements using a photodetector along the x, y, and z axes (in a Bloch sphere picture) on such Fock-state qubits shall be worked out, taking the W state as our entangled system. This will, by the same token, allow us to determine the minimum quantum efficiency required to perform a conclusive Bell test with the W energy eigenstate.

  • 96. Laghaout, Amine
    et al.
    Björk, Gunnar
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Andersen, Ulrik L.
    Realistic limits on the nonlocality of an N-partite single-photon superposition2011Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 84, nr 6, s. 062127-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A recent paper [L. Heaney, A. Cabello, M. F. Santos, and V. Vedral, New J. Phys. 13, 053054 (2011)] revealed that a single quantum symmetrically delocalized over N modes, namely a W state, effectively allows for all-versus-nothing proofs of nonlocality in the limit of large N. Ideally, this finding opens up the possibility of using the robustness of the W states while realizing the nonlocal behavior previously thought to be exclusive to the more complex class of Greenberger-Horne-Zeilinger states. We show that in practice, however, the slightest decoherence or inefficiency of the Bell measurements on W states will degrade any violation margin gained by scaling to higher N. The nonstatistical demonstration of nonlocality is thus proved to be impossible in any realistic experiment.

  • 97.
    Larson, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Level crossings in a cavity QED model2006Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 73, nr 1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper I study the dynamics of a two-level atom interacting with a standing-wave field. When the atom is subjected to a weak linear force, the problem can be turned into a time-dependent one, and the evolution is understood from the band structure of the spectrum. The presence of level crossings in the spectrum gives rise to Bloch oscillations of the atomic motion. Here I investigate the effects of the atom-field detuning parameter. A variety of different level crossings are obtained by changing the magnitude of the detuning, and the behavior of the atomic motion is strongly affected due to this. I also consider the situation in which the detuning is oscillating in time, and its impact on the atomic motion. Wave-packet simulations of the full problem are treated numerically and the results are compared with analytical solutions given by the standard Landau-Zener and the three-level Landau-Zener models.

  • 98.
    Larson, Jonas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Andersson, E.
    Univ. Strathclyde.
    Cavity-state preparation using adiabatic transfer2005Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 71, nr 5Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We show how to prepare a variety of cavity field states for multiple cavities. The state preparation technique used is related to the method of stimulated adiabatic Raman passage. The cavity modes are coupled by atoms, making it possible to transfer an arbitrary cavity field state from one cavity to another and also to prepare nontrivial cavity field states. In particular, we show how to prepare entangled states of two or more cavities, such as an Einstein-Podolsky-Rosen state and a W state, as well as various entangled superpositions of coherent states in different cavities, including Schrodinger cat states. The theoretical considerations are supported by numerical simulations.

  • 99.
    Larson, Jonas
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Garraway, B. M.
    Stenholm, Stig
    KTH, Tidigare Institutioner, Fysik.
    Transient effects on electron spin observation2004Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 69, nr 3, s. 032103-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In an earlier publication we addressed the problem of splitting an electron beam in the Stern-Gerlach experiment. In contrast to arguments put forward in the early days of quantum theory, we concluded that there are no issues of principle preventing the observation of electron spin during free flight. In that paper, however, we considered only a sudden switch off of the separating magnetic field. In this work we consider the possible effects of finite switching times at the beginning and the end of the interaction period. We consider a model where the coupling between the electron and the field is time dependent. As a result of the time dependence, the field also acquires an electric component, but this seems to cause no significant change of our conclusions. On the other hand, the smooth change of the interaction enforces the same longitudinal velocity on the electron both at the beginning and end of the interaction period because of conservation laws; this effect was missing in our earlier calculations. As the electrons are supposed to travel as a beam, this feature helps by restoring the beam quality after the interaction.

  • 100.
    Larson, Jonas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Salo, Janne
    Stenholm, Stig
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Effective mass in cavity QED2005Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 72, nr 1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We consider propagation of a two-level atom coupled to one electromagnetic mode of a high-Q cavity. The atomic center-of-mass motion is treated quantum mechanically and we use a standing wave shape for the mode. The periodicity of the Hamiltonian leads to a spectrum consisting of bands and gaps, which is studied from a Floquet point of view. Based on the band theory, we introduce a set of effective mass parameters that approximately describe the effect of the cavity on the atomic motion, with the emphasis on one associated with the group velocity and on another one that coincides with the conventional effective mass. Propagation of initially Gaussian wave packets is also studied using numerical simulations and the mass parameters extracted thereof are compared with those predicted by the Floquet theory. Scattering and transmission of the wave packet against the cavity are further analyzed, and the constraints for the effective mass approach to be valid are discussed in detail.

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