Electrical detection of spin echoes for phosphorus donors in silicon

The electrical detection of spin echoes via echo tomography is used to observe decoherence processes associated with the electrical readout of the spin state of phosphorus donor electrons in silicon near a SiO$_2$ interface. Using the Carr-Purcell pulse sequence, an echo decay with a time constant of $1.7\pm0.2 \rm{\mu s}$ is observed, in good agreement with theoretical modeling of the interaction between donors and paramagnetic interface states. Electrical spin echo tomography thus can be used to study the spin dynamics in realistic spin qubit devices for quantum information processing.Comment: 14 pages, 3 figure

External field control of donor electron exchange at the Si/SiO2 interface

We analyze several important issues for the single- and two-qubit operations in Si quantum computer architectures involving P donors close to a SiO2 interface. For a single donor, we investigate the donor-bound electron manipulation (i.e. 1-qubit operation) between the donor and the interface by electric and magnetic fields. We establish conditions to keep a donor-bound state at the interface in the absence of local surface gates, and estimate the maximum planar density of donors allowed to avoid the formation of a 2-dimensional electron gas at the interface. We also calculate the times involved in single electron shuttling between the donor and the interface. For a donor pair, we find that under certain conditions the exchange coupling (i.e. 2-qubit operation) between the respective electron pair at the interface may be of the same order of magnitude as the coupling in GaAs-based two-electron double quantum dots where coherent spin manipulation and control has been recently demonstrated (for example for donors ~10 nm below the interface and \~40 nm apart, J~10^{-4} meV), opening the perspective for similar experiments to be performed in Si.Comment: 11 pages, 15 figures. Changes in Eq. 24 plus minor typo

Electron Paramagnetic Resonance of Boron Acceptors in Isotopically Purified Silicon

The electron paramagnetic resonance (EPR) linewidths of B acceptors in Si are found to reduce dramatically in isotopically purified 28Si single crystals. Moreover, extremely narrow substructures in the EPR spectra are visible corresponding to either an enhancement or a reduction of the absorbed microwave on resonance. The origin of the substructures is attributed to a combination of simultaneous double excitation and spin relaxation in the four level spin system of the acceptors. A spin population model is developed which qualitatively describes the experimental results.Comment: 4 pages, 3 figure

Tarifabschluss im öffentlichen Dienst - die große Tarifrechtsreform?

Stellt der Tarifabschluss für Arbeiter und Angestellte von Bund und Kommunen einen Beitrag zum Einstieg in eine umfassende Neustrukturierung des öffentlichen Dienstes dar, oder wurde vor allem an den bisherigen alten Strukturen des öffentlichen Dienstes festgehalten? Für Dr. Thomas Böhle, Vereinigung der Kommunalen Arbeitgeberverbände, wird "das bisherige Tarifrecht … durch ein modernes, leistungsorientiertes und transparentes Tarifrecht ersetzt, das den Anforderungen einer modernen Verwaltung für die Bürgerinnen und Bürger gerecht wird". Auch Dr. Ralf Stegner, Finanzminister des Landes Schleswig-Holstein, sieht positive Elemente: "Der Potsdamer Tarifabschluss vom 9. Februar 2005 ist der erste Baustein zur großen Tarifrechtsreform durch Einführung einer neuen Entgeltordnung, in dem auch die Gewerkschaften durchaus ihre Reformfähigkeit unter Beweis gestellt haben.… Im Detail gibt es aus Ländersicht aber auch kritisch zu hinterfragende Entscheidungen." Weitaus skeptischer ist Prof. Dr. Walter A. Oechsler, Universität Mannheim: "Die Analyse macht deutlich, dass die Tarifreform nicht die große durchgreifende Modernisierung des Tarifrechts im öffentlichen Dienst darstellt." Nach Ansicht von Prof. Dr. Monika Böhm, Universität Marburg, stellt der Tarifvertrag einen wichtigen Beitrag zum Einstieg in eine umfassend erforderliche Neustrukturierung des öffentlichen Dienstes dar, obwohl weitgehend an den bisherigen Strukturen festgehalten wurde.Öffentlicher Dienst, Angestellte, Arbeiter, Tariflohn, Leistungsorientierte Vergütung, Tarifvertrag, Deutschland

Ripple and kink dynamics

We propose a relevant modification of the Nishimori-Ouchi model [{\em Phys. Rev. Lett.} {\bf 71}, 197 (1993)] for granular landscape erosion. We explicitly introduce a new parameter: the angle of repose $\theta_r$, and a new process: avalanches. We show that the $\theta_r$ parameter leads to an asymmetry of the ripples, as observed in natural patterns. The temporal evolution of the maximum ripple height $h_{max}$ is limited and not linear, according to recent observations. The ripple symmetry and the kink dynamics are studied and discussed.Comment: 7 pages, 10 figure, RevTe

What can asymptotic expansions tell us about large-scale quasi-geostrophic anticyclonic vortices?

International audienceThe problem of the large-scale quasi-geostrophic anticyclonic vortices is studied in the framework of the baratropic rotating shallow- water equations on the ß-plane. A systematic approach based on the multiplescale asymptotic expansions is used leading to a hierarchy of governing equations for the large-scale vortices depending on their characteristic size, velocity and a free surface elevation. Among them are the Charney-Obukhov equation, the intermediate geostrophic model equation, the frontal dynamics equation and some new nonlinear quasi-geostrophic equation. We are looking for steady-drifting axisymmetric anticyclonic solutions and find them in a consistent way only in this last equation. These solutions are soliton-like in the sense that the effects of weak non-linearity and dispersion balance each other. The same regimes on the paraboloidal ß-plane are studied, all giving a negative result in what concerns the axisymmetric steady solutions, except for a strong elevation case where any circular profile is found to be steadily propagating within the accuracy of the approximation