3,006 research outputs found
Compton scattering of twisted light: angular distribution and polarization of scattered photons
Compton scattering of twisted photons is investigated within a
non-relativistic framework using first-order perturbation theory. We formulate
the problem in the density matrix theory, which enables one to gain new
insights into scattering processes of twisted particles by exploiting the
symmetries of the system. In particular, we analyze how the angular
distribution and polarization of the scattered photons are affected by the
parameters of the initial beam such as the opening angle and the projection of
orbital angular momentum. We present analytical and numerical results for the
angular distribution and the polarization of Compton scattered photons for
initially twisted light and compare them with the standard case of plane-wave
light
Multipartite W states for chains of atoms conveyed through an optical cavity
We propose and work out a scheme to generate the entangled W states for a
chain of N four-level atoms which are transported through an optical cavity by
means of an optical lattice. This scheme is based on the combined laser-cavity
mediated interaction between distant and equally separated atoms and works in a
completely deterministic way for qubits encoded by two hyperfine levels of the
atoms. Only two parameters, namely the distance between the atoms and the
velocity of the chain, determine the effective interaction among the atoms and,
therefore, the degree of entanglement that is obtained for the overall chain of
N qubits. In particular, we work out the parameter regions for which the W
states are generated most reliably for chains of N = 2,3,4 and 5 atoms. In
addition, we analyze the sensitivity in the formation of entanglement for such
chains of qubits due to uncertainties produced by the oscillations of atoms in
optical lattices.Comment: 12 pages, revised version accepted in PR
Many-electron effects on the x-ray Rayleigh scattering by highly charged He-like ions
The Rayleigh scattering of x-rays by many-electron highly charged ions is
studied theoretically. The many-electron perturbation theory, based on a
rigorous quantum electrodynamics approach, is developed and implemented for the
case of the elastic scattering of (high-energetic) photons by helium-like ion.
Using this elaborate approach, we here investigate the many-electron effects
beyond the independent-particle approximation (IPA) as conventionally employed
for describing the Rayleigh scattering. The total and angle-differential cross
sections are evaluated for the x-ray scattering by helium-like Ni,
Xe, and Au ions in their ground state. The obtained results
show that, for high-energetic photons, the effects beyond the IPA do not exceed
2% for the scattering by a closed -shell.Comment: 15 pages, 11 figure
Hyperfine-induced effects on the linear polarization of the K emission from helium-like ions
The linear polarization of the characteristic photon emission from
few-electron ions is studied for its sensitivity with regard to the nuclear
spin and magnetic moment of the ions. Special attention is paid, in particular,
to the K (1s 2p_{3/2} ^{1,3}P_{1,2} \to 1s^2 ^1S_0) decay of
selected helium-like ions following the radiative electron capture into
initially hydrogen-like species. Based on the density matrix theory, a unified
description is developed that includes both, the many-electron and hyperfine
interactions as well as the multipole-mixing effects arising from the expansion
of the radiation field. It is shown that the polarization of the K
line can be significantly affected by the mutipole mixing between the leading
and hyperfine-induced components of 1s2p ^3P_2, F_i \to 1s^2 ^1S_0,
F_f transitions. This - mixing strongly depends on the nuclear
properties of the considered isotopes and can be addressed experimentally at
existing heavy-ion storage rings
Discrete Dirac system: rectangular Weyl functions, direct and inverse problems
A transfer matrix function representation of the fundamental solution of the
general-type discrete Dirac system, corresponding to rectangular Schur
coefficients and Weyl functions, is obtained. Connections with Szeg\"o
recurrence, Schur coefficients and structured matrices are treated.
Borg-Marchenko-type uniqueness theorem is derived. Inverse problems on the
interval and semiaxis are solved.Comment: Section 2 is improved in the second version: some new results on
Halmos extension are added and arguments are simplifie
Copyrightability of Music Compilations and Playlists: Original and Creative Works of Authorship?
Music compilations and playlists have a common nucleus of an act of gathering songs and ordering them. Their selection and arrangement can be decisive of the success and therefore can be valuable. And here is where the legal issues about their ownership arise: Are music compilations and playlists protectable under the regime of Copyright Law? This article will discuss the legal and practical issues connected with that question. Thereby, it will consider the United States, Europe in general and also the United Kingdom and Germany in particular. The individual legal systems and statutes will be analyzed, as well as the comprehensive jurisprudence. Finally, the most recent developments in the matter will be discussed
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