Showing papers in "Journal of Physics B in 2008"
TL;DR: In this article, a complete understanding of the way in which attosecond pulses arrive at a target where they can be characterized and used in an experiment is discussed, and a number of results from calculations of the attoscond pulse generation obtained by simultaneous solution of the time-dependent Schrodinger equation and the Maxwell wave equation are discussed.
Abstract: Attosecond pulses are generated by a macroscopic number of ionizing atoms interacting with a focused laser pulse, via the process of high harmonic generation. The physics of their generation consists of an interplay between the microscopic laser–atom interaction and macroscopic effects due to ionization and phase matching in the nonlinear medium. In this review, we focus on a complete understanding of the way in which attosecond pulses arrive at a target where they can be characterized and used in an experiment. We discuss a number of results from calculations of attosecond pulse generation obtained by simultaneous solution of the time-dependent Schrodinger equation and the Maxwell wave equation. These results, which allow for a clean separation of microscopic and macroscopic factors, illustrate how macroscopic effects are used to select attosecond pulses from the radiation that is emitted by atoms interacting with a strong laser field.
304 citations
TL;DR: The theoretical description of trapped weakly interacting Bose-Einstein condensates is characterized by a large number of seemingly very different approaches which have been developed over the course of time by researchers with very distinct backgrounds.
Abstract: The theoretical description of trapped weakly interacting Bose–Einstein condensates is characterized by a large number of seemingly very different approaches which have been developed over the course of time by researchers with very distinct backgrounds. Newcomers to this field, experimentalists and young researchers all face a considerable challenge in navigating through the 'maze' of abundant theoretical models, and simple correspondences between existing approaches are not always very transparent. This tutorial provides a generic introduction to such theories, in an attempt to single out common features and deficiencies of certain 'classes of approaches' identified by their physical content, rather than their particular mathematical implementation. This tutorial is structured in a manner accessible to a non-specialist with a good working knowledge of quantum mechanics. Although some familiarity with concepts of quantum field theory would be an advantage, key notions, such as the occupation number representation of second quantization, are nonetheless briefly reviewed. Following a general introduction, the complexity of models is gradually built up, starting from the basic zero-temperature formalism of the Gross–Pitaevskii equation. This structure enables readers to probe different levels of theoretical developments (mean field, number conserving and stochastic) according to their particular needs. In addition to its 'training element', we hope that this tutorial will prove useful to active researchers in this field, both in terms of the correspondences made between different theoretical models, and as a source of reference for existing and developing finite-temperature theoretical models.
237 citations
TL;DR: In this article, the Doppler-broadened absorption of a weak monochromatic probe beam in a thermal rubidium vapour cell on D lines was studied. And the absorption and refractive index as a function of frequency were expressed in terms of the complementary error function.
Abstract: We study the Doppler-broadened absorption of a weak monochromatic probe beam in a thermal rubidium vapour cell on D lines. A detailed model of the susceptibility is developed which takes into account the absolute linestrengths of the allowed electric dipole transitions and the motion of the atoms parallel to the probe beam. All transitions from both hyperfine levels of the ground term of both isotopes are incorporated. The absorption and refractive index as a function of frequency are expressed in terms of the complementary error function. The absolute absorption profiles are compared with experiment, and are found to be in excellent agreement provided a sufficiently weak probe beam with an intensity under one-thousandth of the saturation intensity is used. The importance of hyperfine pumping for open transitions is discussed in the context of achieving the weak-probe limit. Theory and experiment show excellent agreement, with an rms error better than 0.2% for the D2 line at 16.5 °C.
191 citations
TL;DR: In this paper, Alice, Bob and Charlie are three remote parties sharing the classical knowledge of a secret qubit state, and Alice and Bob share the knowledge of how to prepare the qubit states for Charlie.
Abstract: Alice, Bob and Charlie are three remote parties Alice and Bob share the classical knowledge of a secret qubit state We consider the following question: 'how can Alice and Bob jointly prepare the qubit state for Charlie?' Two different protocols are proposed for such a joint remote state preparation The first protocol uses a single GHZ state while the second one uses a pair of EPR states as the quantum channel whose entanglement is not necessarily maximal
170 citations
TL;DR: In this paper, the authors review the relevance of these operations to some of the fundamental aspects of quantum physics and recent advances in this research and present a tutorial on how to generate a photonic state at will.
Abstract: Annihilating and creating a photon in a travelling light field are useful building blocks for quantum-state engineering to generate a photonic state at will In this tutorial, we review the relevance of these operations to some of the fundamental aspects of quantum physics and recent advances in this research
169 citations
TL;DR: In this paper, a tripartite scheme for securely sharing an arbitrary two-qubit quantum information (i.e., a quantum state) is shown. And the optimal scheme has the distinct advantages of consuming fewer quantum and classical resources, lessening the difficulty and intensity of necessary operations, and having higher intrinsic efficiency.
Abstract: An original idea is proposed for constructing optimal schemes of quantum-state sharing with respect to resource consumption, operation complexity and efficiency. To elucidate it, a specific tripartite scheme for securely sharing an arbitrary two-qubit quantum information (i.e., a quantum state) is shown. Compared with the three schemes proposed recently (Deng et al 2005 Phys. Rev. A 72 044301, 2006 Eur. Phys. J. D 39 459), the optimal scheme has the distinct advantages of consuming fewer quantum and classical resources, lessening the difficulty and intensity of necessary operations, and having higher intrinsic efficiency.
114 citations
TL;DR: In this article, it was shown that diatomic molecules interacting with standing laser waves produce periodic arrays of conical intersections, where the translational and rovibrational motions become strongly coupled to each other.
Abstract: Conical intersections of potential energy surfaces widely appear in molecules which consist of more than two atoms. No conical intersections exist in the case of free diatomic molecules. We show here that diatomic molecules interacting with standing laser waves produce periodic arrays of conical intersections. At these laser-induced intersections the non-adiabatic effects are infinitely strong. The translational and rovibrational molecular motions become strongly coupled to each other and energy exchange between the various degrees of freedom influences the dynamics of the system. As an illustrative example, an effect of the laser-induced conical intersections on trapping of ultracold diatomic molecules by light is discussed.
107 citations
TL;DR: In this article, the first measurements and detailed analysis of extreme ultraviolet (EUV) spectra of highly-charged tungsten ions W54+ to W63+ obtained with an electron beam ion trap (EBIT) are presented.
Abstract: We report the first measurements and detailed analysis of extreme ultraviolet (EUV) spectra (4–20 nm) of highly-charged tungsten ions W54+ to W63+ obtained with an electron beam ion trap (EBIT). Collisional-radiative modelling is used to identify strong electric-dipole and magnetic-dipole transitions in all ionization stages. These lines can be used for impurity transport studies and temperature diagnostics in fusion reactors, such as ITER. Identifications of prominent lines from several W ions are confirmed by the measurement of isoelectronic EUV spectra of Hf, Ta and Au. We also discuss the importance of charge-exchange recombination for the correct description of ionization balance in the EBIT plasma.
102 citations
TL;DR: In this paper, a pair of bosonic particles in a one-dimensional tight-binding periodic potential described by the Hubbard model with an attractive or repulsive on-site interaction is considered.
Abstract: We consider a pair of bosonic particles in a one-dimensional tight-binding periodic potential described by the Hubbard model with an attractive or repulsive on-site interaction. We derive explicit analytic expressions for the two-particle states, which can be classified as (i) scattering states of asymptotically free particles and (ii) interaction-bound dimer states. Our results provide a very transparent framework to understand the properties of interacting pairs of particles in a lattice.
100 citations
TL;DR: In this paper, a time-dependent density functional theory is used to calculate the total and subshell photoionization cross sections of C60 and reveal two collective plasmon resonances in the total cross section in agreement with the experiment.
Abstract: Time-dependent density functional theory is used to calculate the total and subshell photoionization cross sections of C60. The core of 60 C4+ ions is smeared into a classical jellium shell before treating the correlated motion of the 240 valence electrons quantum mechanically. The calculation reveals two collective plasmon resonances in the total cross section in agreement with the experiment. It is found that a phase-coherent superposition of amplitudes leading to enhancements in the ionization from various C60 subshells in two distinct energy regions essentially builds the plasmons. While the result shows good qualitative agreement with the experiments, the limitation of the model to describe the data in quantitative detail is discussed.
91 citations
TL;DR: The reductive perturbation method is a very powerful way of deriving simplified models describing nonlinear wave propagation and interaction as mentioned in this paper, and it has been applied in many applications, such as ultrafast or wave propagation in ferromagnetic media.
Abstract: The reductive perturbation method is a very powerful way of deriving simplified models describing nonlinear wave propagation and interaction. In abstract frames chosen for the sake of clarity, we describe the fundamentals of the method: envelope equations, long-wave approximation, three-wave resonant interaction. We give an insight into the mathematical properties of the perturbative schemes. Then some applications are given, which either illustrate the typical situation or introduce additional features of perturbative expansions, and have their own physical interest. The applications concern either nonlinear optics, especially ultrafast, or wave propagation in ferromagnetic media, in the so-called electromagnetic or polariton range.
TL;DR: In this paper, the ionization and charge separation processes of nanoplasmas created by resonant excitation of atomic clusters in intense soft x-ray pulses have been investigated through irradiation with femtosecond pulses from the FLASH free electron laser (FEL) at 13.7 nm and power densities exceeding 1014 W cm.
Abstract: The ionization and charge separation processes of nanoplasmas created by resonant excitation of atomic clusters in intense soft x-ray pulses have been investigated. Through irradiation with femtosecond pulses from the FLASH free electron laser (FEL) at ? = 13.7 nm and power densities exceeding 1014 W cm?2 the clusters are highly ionized with transient atomic charge states up to 9+. Variation of the cluster composition from pristine to doped and core?shell systems allows tracking of the spatial origin and charge states of the fragments yielding insight into the nanoplasma dynamics. The data give evidence for efficient charge redistribution processes leading to a Coulomb explosion of the cluster outer part and recombination of the nanoplasma core. The experiments show qualitatively different processes for (soft) x-ray produced nanoplasmas from the optical (IR) strong-field regime where the clusters disintegrate completely in a Coulomb explosion.
TL;DR: In this paper, high-order harmonic generation up to the 55th order was achieved using 15 nm and 110 nm silver nanoparticle-containing plumes, when femtosecond radiation propagated through the preformed plasma.
Abstract: High-order harmonic generation up to the 55th order was achieved using 15 nm and 110 nm silver nanoparticle-containing plumes, when femtosecond radiation propagated through the preformed plasma. These results are compared with the high-order harmonics generated from the plasma produced on the surface of bulk silver at different delays between the subnanosecond prepulse and the femtosecond pulse.
TL;DR: In this article, the photon statistics in the light emitted by a microcavity containing a semiconductor quantum well were investigated and an analytical expression of the light-emitted autocorrelation function in the weak pumping regime was derived.
Abstract: We investigate the photon statistics in the light emitted by a microcavity containing a semiconductor quantum well. An analytical expression of the light-emitted autocorrelation function in the weak pumping regime is derived. We discuss photon statistical similarities with an atomic cavity.
TL;DR: In this article, the authors measured the relative (e,2e) triply differential cross sections (TDCS) for the ionization of the helium atom and the hydrogen molecule in coplanar asymmetric geometry at a scattered electron energy of 500 eV and ejected electron energies of 205, 74 and 37 eV.
Abstract: Relative (e,2e) triply differential cross sections (TDCS) are measured for the ionization of the helium atom and the hydrogen molecule in coplanar asymmetric geometry at a scattered electron energy of 500 eV and ejected electron energies of 205, 74 and 37 eV. The He experimental results are found to be in very good agreement with convergent close-coupling calculations (CCC). The H2 experimental results are compared with two state-of-the-art available theoretical models for treating differential electron impact ionization of molecules. Both models yield an overall good agreement with experiments, except for some intensity deviations in the recoil region. Similar (e,2e) works were recently published on H2 with contrasted conclusions to the hypothesis that the two H nuclei could give rise to an interference pattern in the TDCS structure. Murray (2005 J. Phys. B: At. Mol. Opt. Phys. 38 1999) found no evidence for such an effect, whereas Milne-Brownlie et al (2006 Phys. Rev. Lett. 96 233201) reported its indirect observation. In this work, based on a direct comparison between experimental results for He and H2, we observe an oscillatory pattern due to these interference effects, and for the first time the destructive or constructive character of the interference is observed, depending on the de Broglie wavelength of the ejected electron wave. The experimental finding is in good agreement with the theoretical prediction by Stia et al (2003 J. Phys. B: At. Mol. Opt. Phys. 36 L257).
TL;DR: In this article, an efficient approach to describe electron dynamics in molecules is developed which exploits quantum dynamics and quantum chemistry in a new way, and the photodissociation of D+2 which can be controlled via the carrier-envelope phase of an ultrashort laser pulse is chosen as a test system.
Abstract: An efficient approach to describe electron dynamics in molecules is developed which exploits quantum dynamics and quantum chemistry in a new way. The photodissociation of D+2 which can be controlled via the carrier-envelope phase of an ultrashort laser pulse is chosen as a test system. In this system, the approach is checked against more rigorous theories as well as experiments which show excellent agreement. The electron dynamics is visualized in several ways including the phase information of the electronic wavefunction. The detailed analysis of the electron motion after different ionization events reveals the underlying complex dynamics which are hidden in the experiment. The interplay between the carrier-envelope phase and electron control is elucidated. The ansatz is based on the highly developed electronic structure theory and can be implemented quite easily. The method allows for a successive extension to multi-electron systems and simultaneously enables a quantum-dynamical description of the nuclear motion.
TL;DR: In this paper, the locking phenomena arising when an external-cavity diode laser is subjected to optical injection from another uncontrolled diode, and the system stability is investigated as a function of coupled cavity time delay and the optical injection strength.
Abstract: We analyse the locking phenomena arising when an external-cavity diode laser is subjected to optical injection from another uncontrolled diode laser. The system stability is investigated as a function of coupled cavity time delay and the optical injection strength. Different regimes, spanning from 'in-phase locking' to 'out-of-phase locking' with ultimate amplitude death of low-frequency fluctuations/pulsations, are described experimentally as well as numerically for weak to moderate injection. Qualitative agreements between numerically and experimentally observed results for amplitude quenching are shown. Numerical studies describe the shifting of phase-flip bifurcation as the optical injection strength is varied for a particular time delay. Stable phase-locking behaviours, which are desired from the point of view of practical applications, are observed numerically in a wide range of control parameter space.
TL;DR: Two quantum information splitting schemes using respectively tripartite GHZ and asymmetric W states as quantum channels are presented, showing that if the secret state is chosen from a special ensemble and known to the sender (Alice), then she can split and distribute it to the receivers Bob and Charlie by performing only a single-qubit measurement and broadcasting a one-cbit message.
Abstract: We present two quantum information splitting schemes using respectively tripartite GHZ and asymmetric W states as quantum channels. We show that if the secret state is chosen from a special ensemble and known to the sender (Alice), then she can split and distribute it to the receivers Bob and Charlie by performing only a single-qubit measurement and broadcasting a one-cbit message. It is clear that no other schemes could possibly achieve the same goal with simpler measurement and less classical communication. In comparison, existing schemes work for arbitrary quantum states which need not be known to Alice; however she is required to perform a two-qubit Bell measurement and communicate a two-cbit message. Hence there is a trade-off between flexibility and measurement complexity plus classical resource. In situations where our schemes are applicable, they will greatly reduce the measurement complexity and at the same time cut the communication overhead by one half.
TL;DR: In this article, the authors studied electromagnetically induced transparency (EIT) of a weakly interacting cold Rydberg gas and showed that the onset of interactions is manifest as a depopulation of the Rydenberg state.
Abstract: We study electromagnetically induced transparency (EIT) of a weakly interacting cold Rydberg gas. We show that for Rydberg states with principal quantum numbers in the range n = 19–26, the onset of interactions is manifest as a depopulation of the Rydberg state. In the limit of a weak probe where the depopulation effect is negligible, we observe no evidence of interaction-induced decoherence and obtain a narrow Rydberg dark resonance with a linewidth of <600 kHz.
TL;DR: A general expression for the angular correlation function of the two emitted photoelectrons in sequential two-photon double ionization of atoms is derived and discussed in this article, which can be used in the analysis of angle-resolved coincidence experiments.
Abstract: A general expression for the angular correlation function of the two emitted photoelectrons in sequential two-photon double ionization of atoms is derived and discussed. The expression can be used in the analysis of angle-resolved coincidence experiments. The angular distributions of the emitted electrons as measured in non-coincidence experiments are also discussed. As an example, the cross sections, angular distributions of photoelectrons and angular correlation functions for the sequential two-photon double ionization of Ne and Ar atoms have been calculated within the MCHF and MCDF approaches. The results are compared with recent experiments performed at the free-electron laser (FLASH) facility.
TL;DR: In this article, a basic rate equation model of a quantum-well semiconductor ring laser is reduced to two equations using asymptotic methods, and an analysis of the bifurcation scenarios in different parameter regimes is pursued.
Abstract: A basic rate equation model of a quantum-well semiconductor ring laser is reduced to two equations using asymptotic methods. The reduced model allows for analytical expressions of the bifurcation points, which will simplify future model parameter estimations, and motivates a two-dimensional phase-space description of the dynamical behaviour. An analysis of the bifurcation scenarios in different parameter regimes is pursued. Physical conditions for the emergence of the operating regimes are assessed quantitatively in terms of saturation processes and backscattering mechanisms.
TL;DR: In this paper, a new type of confinement resonance, termed a correlation confinement resonance occurring in the photoionization of an atom A encapsulated inside the hollow cage of C60, A@C60, is found and interpreted.
Abstract: A new type of confinement resonance, termed a correlation confinement resonance, occurring in the photoionization of an atom A encapsulated inside the hollow cage of C60, A@C60, is found and interpreted in this paper. It is multielectron in nature and is induced in the photoionization of an outer shell of the confined atom by 'ordinary' confinement resonances in photoionization amplitudes from deeper subshells as a result of interchannel coupling. The effect is illustrated by calculations of the 5s photoionization cross section of endohedral Xe, Xe@C60, in the region of the 4d giant resonance exhibiting ordinary confinement resonances.
TL;DR: In this paper, the authors examined the optical preparation of persistent nuclear spin coherences and the retrieval of light pulses both in a Λ-type and a V-type coupling scheme in a Pr3+:Y2SiO5 crystal, cooled to cryogenic temperatures.
Abstract: We examine electromagnetically induced transparency (EIT), the optical preparation of persistent nuclear spin coherences and the retrieval of light pulses both in a Λ-type and a V-type coupling scheme in a Pr3+:Y2SiO5 crystal, cooled to cryogenic temperatures. The medium is prepared by optical pumping and spectral hole burning, creating a spectrally isolated Λ-type and a V-type system within the inhomogeneous bandwidth of the 3H4 ↔ 1D2 transition of the Pr3+ ions. By EIT, in the Λ-type scheme we drive a nuclear spin coherence between the ground-state hyperfine levels, while in the V-type scheme we drive a coherence between the excited-state hyperfine levels. We observe the cancellation of absorption due to EIT and the retrieval of light pulses in both level schemes. This also permits the determination of dephasing times of the nuclear spin coherence, either in the ground state or the optically excited state.
TL;DR: In this paper, the authors discuss the physics of sub-Doppler DAVLL spectroscopy, which employs a pump beam with an axial magnetic field to induce dichroism in an atomic vapour.
Abstract: We discuss the physics of sub-Doppler DAVLL spectroscopy, which employs a pump beam with an axial magnetic field to induce dichroism in an atomic vapour. The dichroism is measured by a counterpropagating probe beam, while the pump generates sub-Doppler spectral features. The magnitude of the field is chosen to shift the frequency of the absorption features by an amount comparable to their linewidth. The reference signals obtained are ideal for laser frequency discriminant signals (laser 'locking' to the atomic transition) without frequency modulation. We discuss the sensitivity of the spectra to magnetic field, laser power and polarization purity, and suggest operating parameters for the 87Rb F = 2 → F' = 3, 2 crossover transition which maximize the signal amplitude and gradient.
TL;DR: A review of the existing theoretical and computational treatments of atomic processes important for understanding the experiments to make and trap the antihydrogen atom is given in this paper, with the emphasis on the behaviour and properties of the charged species in these devices (electrons, positrons and antiprotons).
Abstract: One possible route for a precision test of the CPT theorem is to perform spectroscopic measurements on the antihydrogen atom and compare the results with those from hydrogen. We present a review of the existing theoretical and computational treatments of atomic processes important for understanding the experiments to make and trap the antihydrogen atom. The emphasis of this review is on the behaviour and properties of the charged species in these devices (electrons, positrons and antiprotons) and the properties of the antihydrogen that can be formed.
TL;DR: In this paper, the loading and trapping of ultracold atoms in a one-dimensional permanent magnetic lattice of period 10 µm produced on an atom chip is described, and the experimental conditions trap frequencies of up to 90 kHz and the atoms are trapped at a distance of less than 5 µm from the surface with a measured lifetime of about 450 ms.
Abstract: We report on the loading and trapping of ultracold atoms in a one-dimensional permanent magnetic lattice of period 10 µm produced on an atom chip. The grooved structure which generates the magnetic lattice potential is fabricated on a silicon substrate and coated with a perpendicularly magnetized multilayered TbGdFeCo/Cr film of effective thickness 960 nm. Ultracold atoms are evaporatively cooled in a Z-wire magnetic trap and then adiabatically transferred to the magnetic lattice potential by applying an appropriate bias field. Under our experimental conditions trap frequencies of up to 90 kHz in the magnetic lattice are measured and the atoms are trapped at a distance of less than 5 µm from the surface with a measured lifetime of about 450 ms. These results are important in the context of studies of quantum coherence of neutral atoms in periodic magnetic potentials on an atom chip.
TL;DR: In this paper, an optical switching mechanism for nonlinear photonic crystals doped with an ensemble of noninteracting three-level nanoparticles was investigated, in which an intense pump laser field was used to change the refractive index of the nonlinear optical crystal while a weaker probe field monitored an absorption transition in the nanoparticles.
Abstract: A possible switching mechanism has been investigated for nonlinear photonic crystals doped with an ensemble of non-interacting three-level nanoparticles. In this scheme, an intense pump laser field is used to change the refractive index of the nonlinear photonic crystal while a weaker probe field monitors an absorption transition in the nanoparticles. In the absence of the strong laser field the system transmits the probe field when the resonance energy of the nanoparticles lies near the edge of the photonic band gap due to strong coupling between the photonic crystal and the nanoparticles. However, upon application of an intense pump laser field the system becomes absorbing due to a band edge frequency shift that arises due to a nonlinear Kerr effect which changes the refractive index of the crystal. It is anticipated that the optical switching mechanism described in this work can be used to make new types of photonic devices.
TL;DR: In this paper, high-resolution (80 meV FWHM) measurements of the positron-helium total cross section in the energy range between 1 and 15 eV were presented.
Abstract: We present high-resolution (80 meV FWHM) measurements of the positron–helium total cross section in the energy range between 1 and 15 eV. The absolute magnitude of the cross section is in excellent agreement with recent state-of-the-art theoretical calculations and with previous absolute measurements (e.g. Mizogawa et al). Specific scans in the 1–3 eV and 5–8 eV energy regions reveal no evidence of the structures in the cross section reported by Karwasz et al.
TL;DR: In this article, the authors applied the "forest fire" model to describe the optical field ionization and found that the cumulative action of the applied laser field and holes in the dielectric, created during ionization events, enhances the electron ionization rate by orders of magnitude speeding up the electron avalanche development in early times of the ionization dynamics.
Abstract: The interaction of intense ultra-short laser pulses with dielectrics is studied theoretically using a one-dimensional simulation model. The curl Maxwell's equations are solved coupled to the electron continuity, momentum and energy equations. What is new and innovative in our approach is the application of the 'forest fire' method to describe the optical field ionization. The cumulative action of the applied laser field and holes in the dielectric, created during ionization events, enhances the optical field ionization rate by orders of magnitude speeding up the electron avalanche development in the early times of the ionization dynamics. For peak laser intensity of about 1017 W m−2 (1013 W cm−2) the 'forest fire' model plays a major role in the ionization dynamics and increases the electron density by two orders of magnitude. The underlying mechanisms leading to electron avalanche in dielectrics are investigated for peak laser intensities between 1016 and 3 × 1018 W m−2 and laser pulse durations between 10 fs and 1 ps. It was established that the dominant process for electron multiplication depends only on the laser fluence: for F 4 kJ m−2 (F > 0.4 J cm−2) the collisional ionization is the dominant ionization mechanism. Since for laser pulse duration exceeding 20 fs the threshold for dielectric damage of SiO2 is at least Fthr > 15 kJ m−2 (Fthr > 1.5 J cm−2) (Lenzner et al 1998 Phys. Rev. Lett. 80 4076), the primary cause for dielectric damage is an electron avalanche due to collisional ionization.
TL;DR: In this paper, the authors derived a non-local, complex and ab initio absorption potential within the framework of the relativistic Dirac scattering equations and applied it to elastic scattering of electrons and positrons from the heavy noble gases.
Abstract: We have derived a non-local, complex and ab initio absorption potential within the framework of the relativistic Dirac scattering equations and applied it to elastic scattering of electrons and positrons from the heavy noble gases. We have also developed a perturbation method based on the Hulthen–Kato formalism that enables us to calculate the scattering phase shifts using only real quantities and with a very significant reduction in computational effort. We have used this method to calculate differential cross sections and spin asymmetry parameters for the elastic scattering of electrons from krypton. In addition, we have applied this method to the elastic scattering of positrons from krypton. Our results are compared to experimental measurements and substantial improvements are obtained at intermediate energies with respect to calculations either without an absorption potential or with a semi-empirical absorption potential.