40,394 research outputs found
Conjugate gradient solvers on Intel Xeon Phi and NVIDIA GPUs
Lattice Quantum Chromodynamics simulations typically spend most of the
runtime in inversions of the Fermion Matrix. This part is therefore frequently
optimized for various HPC architectures. Here we compare the performance of the
Intel Xeon Phi to current Kepler-based NVIDIA Tesla GPUs running a conjugate
gradient solver. By exposing more parallelism to the accelerator through
inverting multiple vectors at the same time, we obtain a performance greater
than 300 GFlop/s on both architectures. This more than doubles the performance
of the inversions. We also give a short overview of the Knights Corner
architecture, discuss some details of the implementation and the effort
required to obtain the achieved performance.Comment: 7 pages, proceedings, presented at 'GPU Computing in High Energy
Physics', September 10-12, 2014, Pisa, Ital
Zeno Dynamics in Quantum Statistical Mechanics
We study the quantum Zeno effect in quantum statistical mechanics within the
operator algebraic framework. We formulate a condition for the appearance of
the effect in W*-dynamical systems, in terms of the short-time behaviour of the
dynamics. Examples of quantum spin systems show that this condition can be
effectively applied to quantum statistical mechanical models. Further, we
derive an explicit form of the Zeno generator, and use it to construct Gibbs
equilibrium states for the Zeno dynamics. As a concrete example, we consider
the X-Y model, for which we show that a frequent measurement at a microscopic
level, e.g. a single lattice site, can produce a macroscopic effect in changing
the global equilibrium.Comment: 15 pages, AMSLaTeX; typos corrected, references updated and added,
acknowledgements added, style polished; revised version contains corrections
from published corrigend
Determination of the s-wave Scattering Length of Chromium
We have measured the deca-triplet s-wave scattering length of the bosonic
chromium isotopes Cr and Cr. From the time constants for
cross-dimensional thermalization in atomic samples we have determined the
magnitudes and ,
where . By measuring the rethermalization rate of Cr over a
wide temperature range and comparing the temperature dependence with the
effective-range theory and single-channel calculations, we have obtained strong
evidence that the sign of is positive. Rescaling our Cr
model potential to Cr strongly suggests that is positive,
too.Comment: v3: corrected typo in y-axis scaling of Figs. 3 and
Highly charged ions: optical clocks and applications in fundamental physics
Recent developments in frequency metrology and optical clocks have been based
on electronic transitions in atoms and singly charged ions as references. These
systems have enabled relative frequency uncertainties at a level of a few parts
in . This accomplishment not only allows for extremely accurate time
and frequency measurements, but also to probe our understanding of fundamental
physics, such as variation of fundamental constants, violation of the local
Lorentz invariance, and forces beyond the Standard Model of Physics. In
addition, novel clocks are driving the development of sophisticated technical
applications. Crucial for applications of clocks in fundamental physics are a
high sensitivity to effects beyond the Standard Model and Einstein's Theory of
Relativity and a small frequency uncertainty of the clock. Highly charged ions
offer both. They have been proposed as highly accurate clocks, since they
possess optical transitions which can be extremely narrow and less sensitive to
external perturbations compared to current atomic clock species. The selection
of highly charged ions in different charge states offers narrow transitions
that are among the most sensitive ones for a change in the fine-structure
constant and the electron-to-proton mass ratio, as well as other new physics
effects. Recent advances in trapping and sympathetic cooling of highly charged
ions will in the future enable high accuracy optical spectroscopy. Progress in
calculating the properties of selected highly charged ions has allowed the
evaluation of systematic shifts and the prediction of the sensitivity to the
"new physics" effects. This article reviews the current status of theory and
experiment in the field.Comment: 53 pages, 16 figures, submitted to RM
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