770 research outputs found
Light with tunable non-Markovian phase imprint
We introduce a simple and flexible method to generate spatially non-Markovian
light with tunable coherence properties in one and two dimensions. The unusual
behavior of this light is demonstrated experimentally by probing the far field
and recording its diffraction pattern after a double slit: In both cases we
observe instead of a central intensity maximum a line or cross shaped dark
region, whose width and profile depend on the non-Markovian coherence
properties. Since these properties can be controlled and easily reproduced in
experiment, the presented approach lends itself to serve as a testbed to gain a
deeper understanding of non-Markovian processes
Realization of quantum walks with negligible decoherence in waveguide lattices
Quantum random walks are the quantum counterpart of classical random walks, and were recently studied in the context of quantum computation. Physical implementations of quantum walks have only been made in very small scale systems severely limited by decoherence. Here we show that the propagation of photons in waveguide lattices, which have been studied extensively in recent years, are essentially an implementation of quantum walks. Since waveguide lattices are easily constructed at large scales and display negligible decoherence, they can serve as an ideal and versatile experimental playground for the study of quantum walks and quantum algorithms. We experimentally observe quantum walks in large systems (similar to 100 sites) and confirm quantum walks effects which were studied theoretically, including ballistic propagation, disorder, and boundary related effects
On the relation between the neutrino flux from Centaurus A and the associated diffuse neutrino flux
Based on recent results obtained by the Pierre Auger Observatory (PAO), it
has been hypothesized that Centaurus A (Cen A) is a source of ultra-high-energy
cosmic rays (UHECRs) and associated neutrinos. We point out that the diffuse
neutrino flux may be used to constrain the source model if one assumes that the
ratio between the UHECR and neutrino fluxes outputted by Cen A is
representative for other sources. Under this assumption we investigate the
relation between the neutrino flux from Cen A and the diffuse neutrino flux.
Assuming furthermore that Cen A is the source of two UHECR events observed by
PAO, we estimate the all-sky diffuse neutrino flux to be ~200-5000 times larger
than the neutrino flux from Cen A. As a result, the diffuse neutrino fluxes
associated with some of the recently proposed models of UHECR-related neutrino
production in Cen A are above existing limits. Regardless of the underlying
source model, our results indicate that the detection of neutrinos from Cen A
without the accompanying diffuse flux would mean that Cen A is an exceptionally
efficient neutrino source.Comment: 12 pages, 5 figures, revtex4. Accepted for publication in PRD. (v2)
Expanded significantly compared to the previous version; conclusions remain
vali
Transform-limited pulses are not optimal for resonant multiphoton transitions
Maximizing nonlinear light-matter interactions is a primary motive for
compressing laser pulses to achieve ultrashort transform limited pulses. Here
we show how, by appropriately shaping the pulses, resonant multiphoton
transitions can be enhanced significantly beyond the level achieved by
maximizing the pulse's peak intensity. We demonstrate the counterintuitive
nature of this effect with an experiment in a resonant two-photon absorption,
in which, by selectively removing certain spectral bands, the peak intensity of
the pulse is reduced by a factor of 40, yet the absorption rate is doubled.
Furthermore, by suitably designing the spectral phase of the pulse, we increase
the absorption rate by a factor of 7.Comment: 4 pages, 3 figure
Fission-Residues Produced in the Spallation Reaction 238U+p at 1 A GeV
Fission fragments from 1 A GeV 238U projectiles irradiating a hydrogen target
were investigated by using the fragment separator FRS for magnetic selection of
reaction products including ray-tracing and DE-ToF techniques. The momentum
spectra of 733 identified fragments were analysed to provide isotopic
production cross sections, fission-fragment velocities and recoil momenta of
the fissioning parent nuclei. Besides their general relevance, these quantities
are also demanded for applications. Calculations and simulations with codes
commonly used and recently developed or improved are compared to the data.Comment: 60 pages, 21 figures, 4 tables, 2 appendices (15 pages
The acceleration and storage of radioactive ions for a neutrino factory
The term beta-beam has been coined for the production of a pure beam of
electron neutrinos or their antiparticles through the decay of radioactive ions
circulating in a storage ring. This concept requires radioactive ions to be
accelerated to a Lorentz gamma of 150 for 6He and 60 for 18Ne. The neutrino
source itself consists of a storage ring for this energy range, with long
straight sections in line with the experiment(s). Such a decay ring does not
exist at CERN today, nor does a high-intensity proton source for the production
of the radioactive ions. Nevertheless, the existing CERN accelerator
infrastructure could be used as this would still represent an important saving
for a beta-beam facility. This paper outlines the first study, while some of
the more speculative ideas will need further investigations.Comment: Accepted for publication in proceedings of Nufact02, London, 200
Monolithic WDM Sources And Detectors For The Long Wavelength Fiber Band Based On An InP Grating Multiplexer/demultiplexer
Wavelength Division Multiplexed (WDM) networks are currently attracting considerable attention worldwide. Applications envisaged are wide-ranging - from computer back-plane interconnects and the telephone local loop, through local- and metropolitan- area networks, to wide-area networks involving advanced wavelength routing schemes [1, 2]
Threshold meson production and cosmic ray transport
An interesting accident of nature is that the peak of the cosmic ray
spectrum, for both protons and heavier nuclei, occurs near the pion production
threshold. The Boltzmann transport equation contains a term which is the cosmic
ray flux multiplied by the cross section. Therefore when considering pion and
kaon production from proton-proton reactions, small cross sections at low
energy can be as important as larger cross sections at higher energy. This is
also true for subthreshold kaon production in nuclear collisions, but not for
subthreshold pion production.Comment: 9 pages, 1 figur
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