4,079 research outputs found
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
decays and twisted boundary conditions
We propose a new method to evaluate the Lellouch-L\"uscher factor which
relates the 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
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
Weakly Equivalent Arrays
The (extensional) theory of arrays is widely used to model systems. Hence,
efficient decision procedures are needed to model check such systems. Current
decision procedures for the theory of arrays saturate the read-over-write and
extensionality axioms originally proposed by McCarthy. Various filters are used
to limit the number of axiom instantiations while preserving completeness. We
present an algorithm that lazily instantiates lemmas based on weak equivalence
classes. These lemmas are easier to interpolate as they only contain existing
terms. We formally define weak equivalence and show correctness of the
resulting decision procedure
Prospects for a lattice computation of rare kaon decay amplitudes. II. K →π ν ν ¯ decays
The rare kaon decays are strongly suppressed in the
standard model and widely regarded as processes in which new phenomena, not
predicted by the standard model, may be observed. Recognizing such new
phenomena requires precise standard model prediction for the braching ratio of
with controlled uncertainty for both short-distance and
long-distance contributions. In this work we demonstrate the feasibility of
lattice QCD calculation of the long-distance contribution to rare kaon decays
with the emphasis on . Our methodology covers the
calculation of both - and -exchange diagrams. We discuss the
estimation of the power-law, finite-volume corrections and two methods to
consistently combine the long distance contribution determined by the lattice
methods outlined here with the short distance parts that can be reliably
determined using perturbation theory. It is a subsequent work of our first
methodology paper on , where the focus was made on the
-exchange diagrams.Comment: 47 pages, 5 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
Anomalous Chiral Symmetry Breaking above the QCD Phase Transition
We study the anomalous breaking of U_A(1) symmetry just above the QCD phase
transition for zero and two flavors of quarks, using a staggered fermion,
lattice discretization. The properties of the QCD phase transition are expected
to depend on the degree of U_A(1) symmetry breaking in the transition region.
For the physical case of two flavors, we carry out extensive simulations on a
16^3 x 4 lattice, measuring a difference in susceptibilities which is sensitive
to U_A(1) symmetry and which avoids many of the staggered fermion
discretization difficulties. The results suggest that anomalous effects are at
or below the 15% level.Comment: 10 pages including 2 figures and 1 tabl
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