816 research outputs found
Quantum Entanglement and the Two-Photon Stokes Parameters
A formalism for two-photon Stokes parameters is introduced to describe the
polarization entanglement of photon pairs. This leads to the definition of a
degree of two-photon polarization, which describes the extent to which the two
photons act as a pair and not as two independent photons. This pair-wise
polarization is complementary to the degree of polarization of the individual
photons. The approach provided here has a number of advantages over the density
matrix formalism: it allows the one- and two-photon features of the state to be
separated and offers a visualization of the mixedness of the state of
polarization.Comment: 15 pages, 2 figures, accepted for publication in Opt. Com
Autonomie in IT-Systemen : Ein Konzeptionelles Modell
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Die Erforschung und Anwendung von autonomen Systemen ist momentan in der Informatik ein Themengebiet von wachsendem Interesse. Die Aussicht, mit autonomen Verfahren komplexe Systeme handhabbar zu machen und Kosteneinsparungen bei deren Betrieb zu erzielen, hat bereits die Softwareindustrie auf dieses Thema gelenkt und zu neuartigen Produkten geführt. Andererseits darf die Verlässlichkeit eines Systems nicht aufgrund eines autonomen Verfahrens herabgesetzt werden. Dieses Spannungsfeld ist ein Fokus verschiedener Forschungsbemühungen, um autonome Systeme alltagstauglich zu machen.Beim Gebiet der autonomen Systeme handelt es sich um ein junges Themengebiet, welches noch nicht durch allgemein akzeptierte Definitionen geprägt ist. Dadurch entsteht der Bedarf einer terminologischen Basis, die sich momentan in der Phase der Etablierung befindet. Diese Arbeit beteiligt sich an diesem Prozess und schlägt ein konzeptionelles Modell vor. Dieses Modell benennt die grundlegenden Termini und zeigt deren Zusammenhänge auf. Es beschreibt eine Interpretation der relevanten Begriffe und leitet daraus Relationen ab. Auf diese Weise fördert es das gemeinsame Verständnis und erleichtert die Kommunikation bezüglich spezifischer Fragestellungen innerhalb dieses Gebietes
Entanglement, Mixedness, and Spin-Flip Symmetry in Multiple-Qubit Systems
A relationship between a recently introduced multipartite entanglement
measure, state mixedness, and spin-flip symmetry is established for any finite
number of qubits. It is also shown that, within those classes of states
invariant under the spin-flip transformation, there is a complementarity
relation between multipartite entanglement and mixedness. A number of example
classes of multiple-qubit systems are studied in light of this relationship.Comment: To appear in Physical Review A; submitted 14 May 200
Strangeness Enhancement Scenarios: Fireball or Independent Strings?
Due to the long-standing discrepancy between NA35 and NA36 data on
production, two drastically different scenarios of strangeness enhancement are
still possible. Independent string models, such as the dual parton model, lead
to results close to the NA36 data. On the contrary, the NA35 results can only
be described by introducing full final state rescattering of the produced
particles. The corresponding predictions for central - collisions at
CERN energies differ by a factor 3 to 4. Preliminary data on the net proton
(-) rapidity distribution in - collisions favor the
independent string scenario.Comment: 12 pages, Plain Tex, no figure
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Mesophase Separation and Probe Dynamics in Protein-Polyelectrolyte Coacervates
Protein–polyelectrolyte coacervates are self-assembling macroscopically monophasic biomacromolecular fluids whose unique properties arise from transient heterogeneities. The structures of coacervates formed at different conditions of pH and ionic strength from poly(dimethyldiallylammonium chloride) and bovine serum albumin (BSA), were probed using fluorescence recovery after photobleaching. Measurements of self-diffusion in coacervates were carried out using fluorescein-tagged BSA, and similarly tagged Ficoll, a non-interacting branched polysaccharide with the same size as BSA. The results are best explained by temporal and spatial heterogeneities, also inferred from static light scattering and cryo-TEM, which indicate heterogeneous scattering centers of several hundred nm. Taken together with previous dynamic light scattering and rheology studies, the results are consistent with the presence of extensive dilute domains in which are embedded partially interconnected 50–700 nm dense domains. At short length scales, protein mobility is unobstructed by these clusters. At intermediate length scales, proteins are slowed down due to tortuosity effects within the blind alleys of the dense domains, and to adsorption at dense/dilute domain interfaces. Finally, at long length scales, obstructed diffusion is alleviated by the break-up of dense domains. These findings are discussed in terms of previously suggested models for protein–polyelectrolyte coacervates. Possible explanations for the origin of mesophase separation are offered
Quantum Correlations in non-Markovian Environments
We have studied the analytical Markovian and non-Markovian dynamics of
quantum correlations, such as entanglement, quantum discord and Bell
nonlocalities for three noisy qubits. Quantum correlation as measured by
quantum discord is found to be immune to death contrary to entanglement and
Bell nonlocality for initial GHZ- or W-type mixed states
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