21,036 research outputs found
Single spin probe of Many-Body Localization
We use an external spin as a dynamical probe of many body localization. The
probe spin is coupled to an interacting and disordered environment described by
a Heisenberg spin chain in a random field. The spin-chain environment can be
tuned between a thermalizing delocalized phase and non-thermalizing localized
phase, both in its ground- and high-energy states. We study the decoherence of
the probe spin when it couples to the environment prepared in three states: the
ground state, the infinite temperature state and a high energy N\'eel state. In
the non-thermalizing many body localized regime, the coherence shows scaling
behaviour in the disorder strength. The long-time dynamics of the probe spin
shows a logarithmic dephasing in analogy with the logarithmic growth of
entanglement entropy for a bi-partition of a many-body localized system. In
summary, we show that decoherence of the probe spin provides clear signatures
of many-body localization.Comment: 5 pages, 4 figure
Which long-baseline neutrino experiments are preferable?
We discuss the physics of superbeam upgrades, where we focus on T2KK, a NuMI
beam line based experiment NOvA*, and a wide band beam (WBB) experiment
independent of the NuMI beam line. For T2KK, we find that the Japan-Korea
baseline helps resolve parameter degeneracies, but the improvement due to
correlated systematics between the two detectors (using identical detectors) is
only moderate. For an upgrade of NOvA with a liquid argon detector, we
demonstrate that the Ash River site is preferred compared to alternatives, such
as at the second oscillation maximum, and is the optimal site within the U.S.
For a WBB experiment, we find that high proton energies and long decay tunnels
are preferable. We compare water Cherenkov and liquid argon technologies, and
find the break-even point in detector cost at about 4:1. In order to compare
the physics potential of the different experimental configurations, we use the
concept of exposure to normalize the performance. We find that experiments with
WBBs are the best experimental concept. NOvA* could be competitive with
sufficient luminosity. If > 0.01, a WBB experiment can
perform better than a neutrino factory.Comment: 31 pages, 13 figures, 5 tables. Version to appear in PR
CP, T and CPT violation in future long baseline experiments
I give a short overview about the possibilities and problems related to the
measurement of CP violation in long baseline experiments. Special attention is
paid to the issue of degeneracies and a method for their resolution is
quantitatively discussed. The CP violation reach for different experiments is
compared in dependence of and \dm{21}. Furthermore a
short comment about the possible effects of matter induced T violation is made.
Finally the limits on CPT violation obtainable at a neutrino factory are shown.Comment: Talk presented at NUFACT02, London, 1-6 July, 2002. 3 pages, 2
figure
Superconducting atomic contacts under microwave irradiation
We have measured the effect of microwave irradiation on the dc
current-voltage characteristics of superconducting atomic contacts. The
interaction of the external field with the ac supercurrents leads to replicas
of the supercurrent peak, the well known Shapiro resonances. The observation of
supplementary fractional resonances for contacts containing highly transmitting
conduction channels reveals their non-sinusoidal current-phase relation. The
resonances sit on a background current which is itself deeply modified, as a
result of photon assisted multiple Andreev reflections. The results provide
firm support for the full quantum theory of transport between two
superconductors based on the concept of Andreev bound states
Gribov horizon and BRST symmetry: a pathway to confinement
We summarize the construction of the Gribov-Zwanziger action and how it leads
to a scenario which explains the confinement of gluons, in the sense that the
elementary gluon excitations violate positivity. Then we address the question
of how one can construct operators within this picture whose one-loop
correlation functions have the correct analytic properties in order to
correspond to physical excitations. For this we introduce the concept of
i-particles.Comment: 5 pages, proceedings of XII Mexican Workshop on Particles and Fields
200
Topologically non-trivial quantum layers
Given a complete non-compact surface embedded in R^3, we consider the
Dirichlet Laplacian in a layer of constant width about the surface. Using an
intrinsic approach to the layer geometry, we generalise the spectral results of
an original paper by Duclos et al. to the situation when the surface does not
possess poles. This enables us to consider topologically more complicated
layers and state new spectral results. In particular, we are interested in
layers built over surfaces with handles or several cylindrically symmetric
ends. We also discuss more general regions obtained by compact deformations of
certain layers.Comment: 15 pages, 6 figure
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