Showing papers by "Stephan Fritzsche published in 2009"
TL;DR: Two x-ray measurements on the angular distribution and linear polarization of the 1s2s(2)2p(1/2) J=1-->1s( 2)2s (2)J=0 electric-dipole radiation of high-Z, beryllium-like ions are proposed to serve a stringent test on relativistic corrections to the electron-electron interaction in the presence of strong fields.
Abstract: The Breit interaction typically appears as a---more or less small---correction to the Coulomb repulsion acting among the electrons. We here propose two x-ray measurements on the angular distribution and linear polarization of the $1s2{s}^{2}2{p}_{1/2}\text{ }J=1\ensuremath{\rightarrow}1{s}^{2}2{s}^{2}\text{ }J=0$ electric-dipole radiation of high-$Z$, beryllium-like ions, following the resonant electron capture into initially lithium-like ions, for which the Breit interaction strongly dominates the Coulomb repulsion and leads to a qualitative change in the expected x-ray emission pattern. The proposed measurements are feasible with present-day x-ray detectors and may serve a stringent test on relativistic corrections to the electron-electron interaction in the presence of strong fields.
93 citations
TL;DR: In this article, the authors present kinematically complete data on two-photon double ionization of Ne induced by short (~25 fs) intense (~5 × 1013 W cm−2) free-electron laser pulses at 44 eV.
Abstract: We present kinematically complete data on two-photon double ionization of Ne induced by short (~25 fs) intense (~5 × 1013 W cm−2) free-electron laser pulses at 44 eV. The observed electron energy spectrum points to the dominance of 'sequential' ionization. We analyse state-selective angular distributions as well as the two-electron angular correlation function, and suggest a method to determine the time delay between both ionization steps. The measured angular asymmetry (-) parameters significantly deviate from the results of an earlier non-coincident experiment providing benchmark data for theory.
79 citations
TL;DR: In this article, the angular distribution of emitted electrons is calculated with the dipole amplitudes evaluated within the multiconfigurational Hartree-Fock and Dirac Fock approaches.
Abstract: Sequential two-photon double ionization of Kr atoms is theoretically considered. The angular distribution of emitted electrons is calculated with the dipole amplitudes evaluated within the multiconfigurational Hartree–Fock and Dirac–Fock approaches. The difference in angular distributions for two-photon and single-photon ionization is discussed.
32 citations
TL;DR: In this paper, the relativistic radiative recombination program RERR06 based on the multiconfiguration Dirac-Fock method was used to evaluate the radiative electron capture for the collisions of a U.S. ion with a N.
Abstract: To evaluate the radiative electron capture for the collisions of ${\text{U}}^{89+}$ ion with ${\text{N}}_{2}$, radiative recombination cross sections and the corresponding emitted photon energies are calculated from the ground state $1{s}^{2}2s$ to $1{s}^{2}2sn{l}_{j}\phantom{\rule{0.3em}{0ex}}(2\ensuremath{\le}n\ensuremath{\le}9,0\ensuremath{\le}l\ensuremath{\le}6)$ using the newly developed relativistic radiative recombination program RERR06 based on the multiconfiguration Dirac-Fock method. The x-ray spectra for radiative electron capture in the collision have been obtained by convolving the radiative recombination cross sections and the Compton profile of ${\text{N}}_{2}$. Good agreement is found between the calculated and experimental spectra. In addition, the transition energy levels and probabilities among the 147 levels from the captured $1{s}^{2}2sn{l}_{j}$ have been calculated. From the calculated results, radiative decay cascade processes followed by the radiative electron capture have also been studied with the help of multistep model and coupled rate equations, respectively. The present results not only make us understand the details of the radiative electron captures and the radiative decay cascade spectra in the experiment but also show a more efficient way to obtain the cascade spectra. Finally, the equivalence between the multistep model and coupled rate equations has been shown under a proper condition and the latter can hopefully be extended to investigate other cascade processes.
31 citations
TL;DR: In this paper, the ion sphere model was used for estimating the effect of strongly coupled plasma on the ions within the non-relativistic as well as the relativistic framework.
Abstract: Spectral line positions for the highly stripped helium like carbon, aluminium and argon embedded in
intense plasma environments have been calculated theoretically to compare with the existing data
available from laser plasma experiments. The changes in the ionization potentials for such ions have
been determined and the excitation energies, oscillator strengths and transition probabilities for
the transitions 1s2
1S → 1snp 1P (n=2-5) have been evaluated for the diagnostic
determination of such plasmas. The ion sphere (IS) model was used for estimating the effect of strongly
coupled plasma on the ions within the non-relativistic as well as the relativistic framework. Time dependent
perturbation theory has been applied for obtaining the linear response properties of the ions in the
non-relativistic approximation. The effects of the plasma environment on such properties of the ions under
the Debye screening model with suitable cut off radii have also been considered for comparing the data with
those obtained from the IS model of the plasma.
27 citations
TL;DR: In this article, the authors proposed two schemes to generate two-dimensional two-level Rydberg atoms in the framework of cavity QED, based on the resonant interaction of the atoms in a chain with a bimodal cavity that supports two independent modes of the photon field.
Abstract: We propose two schemes to generate the two-dimensional $2\ifmmode\times\else\texttimes\fi{}N$ and $3\ifmmode\times\else\texttimes\fi{}N$ cluster states by using a chain of (two-level) Rydberg atoms in the framework of cavity QED. These schemes work in a completely deterministic way and are based on the resonant interaction of the atoms in a chain with a bimodal cavity that supports two independent modes of the photon field. We demonstrate that a $2\ifmmode\times\else\texttimes\fi{}N$ cluster state can be generated efficiently with only a single bimodal cavity, while two such cavities are needed to produce a $3\ifmmode\times\else\texttimes\fi{}N$ cluster state. It is shown, moreover, how these schemes can be extended toward the generation of $M\ifmmode\times\else\texttimes\fi{}N$ two-dimensional cluster states.
27 citations
TL;DR: Laser-induced fluorescence of two-photon excited 8p, 9p, J=0, 2 and 5f, 6f,J=2 levels in neutral xenon has been investigated in the pressure regime between 4 and 120 Pa and radiative lifetimes and collisional deactivation rates have been deduced using the Stern-Volmer approach.
Abstract: Laser-induced fluorescence of two-photon excited $8p$, $9p$, $J=0,2$ and $5f$, $6f$, $J=2$ levels in neutral xenon has been investigated in the pressure regime between 4 and 120 Pa. Radiative lifetimes and collisional deactivation rates have been deduced especially for the $5f{[3/2]}_{2}$, $5f{[5/2]}_{2}$, and $8p{[1/2]}_{0}$ levels using the Stern-Volmer approach. The spontaneous lifetimes for $5f{[3/2]}_{2}$, $5f{[5/2]}_{2}$, and $8p{[1/2]}_{0}$ levels are 94, 78, and 207 ns, respectively. These lifetimes have been calculated also by applying extended multiconfiguration Dirac-Fock wave functions and are found in agreement with experiment within $10--25\text{ }%$.
18 citations
TL;DR: In this paper, the authors investigated how a small fraction of energetic beamed electrons influences the diagnostics of the electron density in hot plasmas, based on the intensity ratio R of the helium-like forbidden line to the intercombination lines.
Abstract: We have theoretically investigated how a small fraction of energetic beamed electrons influences the diagnostics of the electron density in hot plasmas, based on the intensity ratio R of the helium-like forbidden line to the intercombination lines. Elaborate calculations of the intensity ratio R have been performed for Ne8+ ions over the range of electron densities 109–1013 cm−3 using an electron distribution (model) that includes both Maxwellian isotropic and monoenergetic beam components. By taking into account all important transitions among the 117 magnetic sublevels of the and 1snl (n = 2–4) configurations, a collisional-radiative model has been applied for determining the populations of the upper-magnetic sublevels of lines. The required collision strengths due to both electron components were computed semi-relativistically in the complementary distorted-wave and Coulomb–Bethe methods. The results are given for temperatures Te of the Maxwellian electron component in the range 2–5 × 106 K and for kinetic energies e0 of the monoenergetic electron component between 0.95 and 4 keV. At low Te and e0 not too high, the anisotropy of the intensity angular distribution of lines is found to have an appreciable effect on the R ratio. The electron density inferred from the intensity ratio R without including the beam effect can be significantly overestimated or underestimated depending upon the emission angle relative to the electron beam direction.
16 citations
TL;DR: The multiconfiguration Dirac-Hartree-Fock theory has been employed to calculate the electric dipole moment of the radium state induced by the nuclear Schiff moment as discussed by the authors.
Abstract: The multiconfiguration Dirac-Hartree-Fock theory has been employed to calculate the electric dipole moment of the $7s6d\text{ }{^{3}D}_{2}$ state of radium induced by the nuclear Schiff moment. The results are dominated by valence and core-valence electron correlation effects. We show that the correlation effects can be evaluated in a converged series of multiconfiguration expansions.
14 citations
01 Nov 2009
TL;DR: Theory of the sequential two-photon double ionization of atoms in the XUV wavelength region is discussed in the context of recent experiments with the free-electron laser.
Abstract: Theory of the sequential two-photon double ionization of atoms in the XUV wavelength region is discussed in the context of recent experiments with the free-electron laser. Angular distributions and angular correlations of photoelectrons are analyzed within the statistical tensor formalism and examples are given for sequential two-photon double ionization of noble gases.
13 citations
TL;DR: In this paper, the double-differential recombination cross section of a free electron into an excited state of a bare, high-Z ion is studied, together with its subsequent decay, within the framework of the density matrix theory and Dirac's relativistic equation.
Abstract: Radiative recombination of a free electron into an excited state of a bare, high-Z ion is studied, together with its subsequent decay, within the framework of the density matrix theory and Dirac's relativistic equation. Special attention is paid to the polarization and angular correlations between the recombination and the decay photons. In order to perform a systematic analysis of these correlations the general expression for the double-differential recombination cross section is obtained by making use of the resonance approximation. Based on this expression, detailed computations for the linear polarization of x-ray photons emitted in the (e, 2 gamma) two-step recombination of uranium ions U92+ are carried out for a wide range of projectile energies.
TL;DR: In this paper, high-resolution angle-resolved photoelectron spectra from Na atoms laser excited and aligned in the 2.5π manifold were investigated experimentally and theoretically in the region of the 2π manifold.
Abstract: High resolution angle-resolved photoelectron spectra from Na atoms laser excited and aligned in the ${\text{Na}}^{\ensuremath{\ast}}$ $2{p}^{6}3p\text{ }{^{2}P}_{3/2}$ state are investigated experimentally and theoretically in the region of the ${\text{Na}}^{+}$ $2{p}^{5}3p$ manifold. A prominent influence of the alignment on the relative line intensities is observed. The measured linear alignment dichroism is in good agreement with the theoretical results obtained in the multiconfigurational Dirac-Fock approximation as well as in a generalized geometrical model, which is extended to the description of angular distributions of photoelectrons from polarized atoms.
01 Jan 2009-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this article, the authors investigated the angular distribution of the Kα hypersatellite radiation following high-Z, helium-like ions following the dielectronic recombination of initially hydrogen-like projectiles in relativistic ion-atom collisions.
Abstract: The angular distribution of the Kα hypersatellite radiation has been investigated for high-Z, helium-like ions following the K − LL dielectronic recombination of initially hydrogen-like projectiles in relativistic ion–atom collisions. A particular strong effect is found for the alignment of the 2s2p1/2J = 1 (spin-forbidden) resonance that changes sign if, in addition to the static Coulomb repulsion, the Breit interaction is taken into account for the resonant electron capture. This change in the alignment of the recombined ion also leads to a remarkable shift in the angular distribution of the subsequent 2s2p1/2J = 1 → 1s2s J = 0 Kα2 photons from a dominantly perpendicular emission to one that occurs in parallel with the ion beam, and vice versa for the 2s2p1/2J = 1 → 1s2s J = 1 line.
TL;DR: In this paper, the authors applied the density matrix and second-order perturbation theory in order to re-analyze the two-photon decay of hydrogen-like ions for the polarization of emitted light.
Abstract: We have applied the density matrix and second-order perturbation theory in order to re-analyze the two-photon decay of hydrogen-like ions for the polarization of emitted light. Special attention is paid to the linear polarization of one of the photons, while the spin state of the second photon is supposed to be unobserved. For such an “angle-polarization” correlation of the two photons we investigate the contributions that arise from non electric-dipole terms in the expansion of the electron-photon interaction. Detailed calculations are performed for the 2s1/2 →1s1/2 and 3d5/2 →1s1/2 transitions in neutral hydrogen as well as in hydrogen-like uranium.
TL;DR: In this article, the authors proposed a scheme to generate an entangled state between two (Λ-type) four-level atoms that interact effectively by means of a detuned optical cavity and a laser beam that acts perpendicularly to the cavity axis.
Abstract: A scheme is proposed to generate an entangled state between two (Λ-type) four-level atoms that interact effectively by means of a detuned optical cavity and a laser beam that acts perpendicularly to the cavity axis. It is shown how the degree of entanglement for two atoms passing through the cavity can be controlled by manipulating their velocity and the (initial) distance between the atoms. In addition, three realistic schemes are suggested to implement the two-qubit gates within the framework of the suggested atom–cavity–laser setup, namely, the i-swap gate, controlled-Z gate and the controlled- gate. For all these schemes, we analyse and discuss the atomic velocities and inter-atomic distances for which these gates are realized most reliably.
TL;DR: In this paper, a model is developed to calculate the cross sections for the loss of any number of electrons from the projectile ion, including the ionization of a single electron and up to the complete stripping of the projectile.
Abstract: The multiple electron loss of heavy projectiles in fast ion-atom collisions has been studied in the framework of the sudden perturbation approximation. Especially, a model is developed to calculate the cross sections for the loss of any number of electrons from the projectile ion, including the ionization of a single electron and up to the complete stripping of the projectile. For a given collision system, that is specified by the (type and charge state of the) projectile and target as well as the collision energy, in fact, the experimental cross sections for just three final states of the projectile are required by this model in order to predict the loss of any number, $N$, of electrons for the same collision system or for any similar system that differs only in the energy or the initial charge state of the projectile ion. The model is simple and can be utilized for both the projectile and target ionization, and without that large computer resources are requested. Detailed computations have been carried out for the multiple electron loss of ${\text{Xe}}^{18+}$ and ${\text{U}}^{6+,10+,28+}$ projectiles in collision with neutral Ar and Ne gas targets.
TL;DR: In this paper, an analytical expression for the dynamic polarization potential is derived for the elastic scattering of light halo nuclei in the Coulomb field of heavy targets, based on the adiabatic motion of the projectile below and close to the barrier.
Abstract: An analytical expression for the dynamic polarization potential is derived for the elastic scattering of light halo nuclei in the Coulomb field of heavy targets. The derivation is based on the adiabatic motion of the projectile below and close to the Coulomb barrier together with a uniform approximation for the Coulomb functions. Detailed computations have been carried out for the elastic scattering of d+{sup 208}Pb and {sup 6}He+{sup 208}Pb at collision energies of 8 and 17.8 MeV and are compared with measurements as far as available. The obtained expression for the dynamic polarization potential is simple and can be applied for any arbitrary system with a dineutron configuration.
TL;DR: An up-date of the Racah module is presented, adopted to Maple 11 and 12, which supports both, algebraic manipulations of expressions from Racah's algebra as well as numerical computations of many functions and symbols from the theory of angular momentum.
22 Jun 2009
TL;DR: In this paper, the first results within an experimental approach to determine relative two-photon absorption cross sections in neutral xenon are presented, and the results show that TALIF schemes including 9p and 6f levels are manifestly weaker compared to schemes including 7p, 8p, 9p, and 5f levels.
Abstract: First results within an experimental approach to determine relative two-photon absorption cross sections in neutral xenon are presented. Two-photon absorption profiles of 7p, 8p, 9p (J=0,2) levels and 5f, 6f (J=2) have been measured. Two-photon absorption laserinduced fluorescence (TALIF) schemes including 9p and 6f levels have been found to be manifestly weaker compared to schemes including 7p, 8p and 5f levels. Investigations have been carried out in pressure regimes between 4 and 200 Pa. Evaluation of two-photon absorption cross sections still require measurements below the TALIF signal saturation limit, which has been estimated for the 5f [5/2]-level.
01 Apr 2009
TL;DR: In this paper, a detailed analysis of the Kα1 decay of the helium-like uranium ions U90+ following radiative electron capture, Coulomb excitation and dielectronic recombination processes is presented.
Abstract: Recent theoretical progress in the study of the x-ray characteristic emission from highly-charged, few-electron ions is reviewed. These investigations show that the bound–state radiative transitions in high–Z ions provide a unique tool for better understanding the interplay between the structural and dynamical properties of heavy ions. In order to illustrate such an interplay, detailed calculations are presented for the Kα1 decay of the helium–like uranium ions U90+ following radiative electron capture, Coulomb excitation and dielectronic recombination processes.
26 Oct 2009
TL;DR: This work introduces the eavesdropping attack on Bennett’s B92 protocol for quantum key distribution (QKD) with a quantum cloning machine (QCM) and demonstrates efficiency of suggested attack and compares it with efficiencies of alternative attacks proposed before.
Abstract: Success of any eavesdropping attack on a quantum cryptographic protocol can be reduced by the legitime users if they partially compare their data. It is important to know for the legitime users what is (necessary and enough) amount of data which should be compared to ensure that (possible) illegitime user has an arbitrary small information about the rest of data. To obtain such amount the legitime users need to know efficiencies of all possible attacks for particular cryptographic protocol. In this work we introduce the eavesdropping attack on Bennett’s B92 protocol for quantum key distribution (QKD) with a quantum cloning machine (QCM). We demonstrate efficiency of suggested attack and compare it with efficiencies of alternative attacks proposed before.
TL;DR: In this paper, a symmetric 1 to 2 quantum cloning machine (QCM) is presented that provides high-fidelity copies with $0.90 \le F \le 0.95$ for all pure (single-qubit) input states from a given meridian of the Bloch sphere.
Abstract: A symmetric 1 to 2 quantum cloning machine (QCM) is presented that provides high-fidelity copies with $0.90 \le F \le 0.95$ for all pure (single-qubit) input states from a given meridian of the Bloch sphere. \cor{Emphasize is placed especially on the states of the (so-called) Eastern meridian, that includes the computational basis states $\ketm{0}, \ketm{1}$ together with the diagonal state $\ketm{+} = \frac{1}{\sqrt{2}} (\ketm{0}
+ \ketm{1})$, for which suggested cloning transformation is shown to be optimal.} In addition, we also show how this QCM can be utilized for eavesdropping in Bennett's B92 protocol for quantum key distribution with a substantial higher success rate than obtained for universal or equatorial quantum copying.
01 Nov 2009
TL;DR: In this article, the role of non electric-dipole contributions to the subsequent x-ray emission of high-Z, helium-like U90+ ions has been investigated.
Abstract: The dielectronic recombination of high-Z, hydrogen-like ions has been studied within the framework of density matrix theory, and with emphasis placed on the alignment of the doubly-excited ions and the role of non electric-dipole contributions to the subsequent x-ray emission. For the formation of the LL resonances of helium-like U90+ ions, it is shown especially that the angular distribution of the Kα1 hypersatellite lines is notably modified by the interference between the leading E1 and the magnetic-quadrupole (M2) transitions.
TL;DR: In this article, an optimal universal unitary Controlled-NOT gate that performs a specific operation on two unknown states of qubits taken from a great circle of the Bloch sphere is presented.
Abstract: An investigation of an optimal universal unitary Controlled-NOT gate that performs a specific operation on two unknown states of qubits taken from a great circle of the Bloch sphere is presented. The deep analogy between the optimal universal C-NOT gate and the `equatorial' quantum cloning machine (QCM) is shown. In addition, possible applications of the universal C-NOT gate are briefly discussed.
01 Nov 2009
TL;DR: An expression for the angular correlation function of the two photoelectrons in the sequential two-photon double ionization (TPDI) of atoms is derived, which can be used for analyzing angle-resolved coincidence experiments as discussed by the authors.
Abstract: An expression for the angular correlation function of the two photoelectrons in the sequential two-photon double ionization (TPDI) of atoms is derived, which can be used for analyzing angle-resolved coincidence experiments. Making use of this expression, we have calculated in particular the cross sections, angular distributions and angular correlation functions for the TPDI of Ne, Ar and Kr atoms. The results are compared with recent experiments from the free-electron laser (FLASH) facility as far as available.
01 Nov 2009
TL;DR: In this article, the inner-shell photoionization of highly charged ions by polarized beam of incident photons and their subsequent radiative decay are studied within the framework of density-matrix theory and by using the multi-configuration Dirac-Fock approach (MCDF).
Abstract: The inner-shell photoionization of highly charged ions by polarized beam of incident photons and their subsequent radiative decay are studied within the framework of density-matrix theory and by using the multi-configuration Dirac-Fock approach (MCDF). Final state density matrix has been derived for the system "photoelectron plus ion" with a well defined geometry. This density matrix allows further to evaluate polarization Stokes parameters for the x-ray photons emitted in the radiative decay of the excited ionic states. Detailed polarization calculations have been performed for the 2p53s→2p6 radiative transitions following ionization of the 2p electron of the sodiumlike iron Fe15+ and uranium U81+ ions.
01 Jan 2009-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this article, the density matrix theory combined with the multiconfiguration Dirac-Fock approach was used to study the linear polarization of the decay X-ray photons.
Abstract: Radiative decay of heavy, few-electron ions following electron capture is studied within the framework of the density matrix theory combined with the multiconfiguration Dirac–Fock approach. Special attention is paid to the linear polarization of the decay X-ray photons. Detailed calculations have been carried out, in particular, for the K α 1 (1 s 2 p 3/2 1,3 P 1,2 → 1 s 2 1 S 0 ) transition in helium-like uranium U 90+ ions. For this line, the characteristic radiation is almost unpolarized as a result of the superposition of its fine-structure 1 P 1 → 1 S 0 and 3 P 2 → 1 S 0 components which are strongly linearly polarized in perpendicular directions.
01 Nov 2009
TL;DR: In this paper, the photoelectron satellite structure of rubidium and cesium has been investigated following the pho-toionization of a nd(n = 3, 4) inner-shell electron.
Abstract: The photoelectron satellite structure of rubidium and cesium has been investigated following the pho-toionization of a nd(n = 3, 4) inner-shell electron. Apart from the intensity ratios of the nd−1 ms monopole and nd−1m'p conjugated satellite lines, we measured for rubidium also the energy dependence of the 3dj 6s/3dj 5s and 3dj 5p/3dj 5s intensity ratios for j = 3/2 and 5/2. When compared with multiconfiguration Dirac-Fock calculations, a reasonable-to-good agreement is found for both, the monopole and conjugated, shake-up probabilities if the relaxation of the bound-state electron density is taken into account in the computation of the photoionization cross sections.