Entanglement generation via a completely mixed nuclear spin bath

We show that qubits coupled sequentially to a mesoscopic static completely mixed spin bath via the Heisenberg interaction can become highly entangled. Straightforward protocols for the generation of multipartite entangled (Greenberger-Horne-Zeilinger-)states are presented. We show the feasibility of an experimental realization in a quantum dot by the hyperfine interaction of an electron with the nuclear spins.Comment: 4+pages, 3 figure

K→(ππ)I=2K\to(\pi\pi)_{I=2} decays and twisted boundary conditions

We propose a new method to evaluate the Lellouch-L\"uscher factor which relates the $\Delta I=3/2$ $K\to\pi\pi$ matrix elements computed on a finite lattice to the physical (infinite-volume) decay amplitudes. The method relies on the use of partially twisted boundary conditions, which allow the s-wave $\pi\pi$ phase shift to be computed as an almost continuous function of the centre-of-mass relative momentum and hence for its derivative to be evaluated. We successfully demonstrate the feasibility of the technique in an exploratory computation.Comment: 19 pages, 7 figure

Effective Quantum Dynamics of Interacting Systems with Inhomogeneous Coupling

We study the quantum dynamics of a single mode/particle interacting inhomogeneously with a large number of particles and introduce an effective approach to find the accessible Hilbert space where the dynamics takes place. Two relevant examples are given: the inhomogeneous Tavis-Cummings model (e.g., N atomic qubits coupled to a single cavity mode, or to a motional mode in trapped ions) and the inhomogeneous coupling of an electron spin to N nuclear spins in a quantum dot.Comment: 9 pages and 10 figures, new version, accepted in Physical Review

475°C Embrittlement and Room Temperature Fatigue of Duplex Stainless Steel

Duplex stainless steels (DSSs) are two-phase materials consisting of both the ferritic and the austenitic phase. The alloys are prone to embrittlement particularly in the temperature range between 280°C and 512°C. This so-called 475°C embrittlement is caused by a decomposition of the ferritic phase into a chromium-rich α' and an iron-rich α phase. The objective of this study is to develop a better understanding of the embrittling process of DSS of type SAF 2205. Embrittled and non-embrittled DSS was fatigue tested in stress-controlled tests at 475°C and in strain-controlled tests at room temperature. The high temperature fatigue tests were stopped at different cycle numbers in order to characterize the changing material conditions by means of room-temperature tensile tests and scanning electron microscopy pictures of the fracture surfaces