1,158 research outputs found
Topological Pumping over a Photonic Fibonacci Quasicrystal
Quasiperiodic lattices have recently been shown to be a non-trivial
topological phase of matter. Charge pumping -- one of the hallmarks of
topological states of matter -- was recently realized for photons in a
one-dimensional (1D) off-diagonal Harper model implemented in a photonic
waveguide array. The topologically nontrivial 1D Fibonacci quasicrystal (QC) is
expected to facilitate a similar phenomenon, but its discrete nature and lack
of pumping parameter hinder the experimental study of such topological effects.
In this work we overcome these obstacles by utilizing a family of topologically
equivalent QCs which ranges from the Fibonacci QC to the Harper model.
Implemented in photonic waveguide arrays, we observe the topological properties
of this family, and perform a topological pumping of photons across a Fibonacci
QC.Comment: 5 pages, 4 figures, comments are welcom
The LeChatelier principle: The long and the short of it
Using ordinary calculus techniques, we investigate the conditions under which LeChatelier effects are signable for finite changes in parameter values. We show, for example, that the short run demand for a factor is always less responsive to price changes than the long run demand, provided that the factor of production and the fixed factor do not switch from being substitutes to being complements (or vice versa) over the relevant range of the price change. The absence of a sign change in the complementarity/substitutability relation holds under conditions that are considerably more general than supermodularity of the production function.postprin
Hanbury Brown and Twiss Correlations of Anderson Localized Waves
When light waves propagate through disordered photonic lattices, they can
eventually become localized due to multiple scattering effects. Here we show
experimentally that while the evolution and localization of the photon density
distribution is similar in the two cases of diagonal and off-diagonal disorder,
the density-density correlation carries a distinct signature of the type of
disorder. We show that these differences reflect a symmetry in the spectrum and
eigenmodes that exists in off-diagonally disordered lattices but is absent in
lattices with diagonal disorder.Comment: 4 pages, 3 figures, comments welcom
Parametric Self-Oscillation via Resonantly Enhanced Multiwave Mixing
We demonstrate an efficient nonlinear process in which Stokes and anti-Stokes
components are generated spontaneously in a Raman-like, near resonant media
driven by low power counter-propagating fields. Oscillation of this kind does
not require optical cavity and can be viewed as a spontaneous formation of
atomic coherence grating
General quasi-non-spreading linear three-dimensional wave-packets
We introduce a general approach for generation of sets of three-dimensional
quasi-non-spreading wavepackets propagating in linear media, also referred to
as linear light bullets. The spectrum of rigorously non-spreading wavepackets
in media with anomalous group velocity dispersion is localized on the surface
of a sphere, thus drastically restricting the possible wavepacket shapes.
However, broadening slightly the spectrum affords the generation of a large
variety of quasi-non-spreading distributions featuring complex topologies and
shapes in space and time that are of interest in different areas, such as
biophysics or nanosurgery. Here we discuss the method and show several
illustrative examples of its potential.Comment: 3 pages, 4 figures, to appear in Optics Letter
Coupled-mode theory for Bose-Einstein condensates
We apply the concepts of nonlinear guided-wave optics to a Bose-Einstein
condensate (BEC) trapped in an external potential. As an example, we consider a
parabolic double-well potential and derive coupled-mode equations for the
complex amplitudes of the BEC macroscopic collective modes. Our equations
describe different regimes of the condensate dynamics, including the nonlinear
Josephson effect for any separation between the wells. We demonstrate
macroscopic self-trapping for both repulsive and attractive interactions, and
confirm our results by numerical simulations.Comment: 4 pages, 5 figures; typos removed, figures amended; submitted to PR
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
Universality of rain event size distributions
We compare rain event size distributions derived from measurements in climatically different regions, which we find to be well approximated by power laws of similar exponents over broad ranges. Differences can be seen in the large-scale cutoffs of the distributions. Event duration distributions suggest that the scale-free aspects are related to the absence of characteristic scales in the meteorological mesoscale
Spatiotemporally Localized Multidimensional Solitons in Self-Induced Transparency Media
"Light bullets" are multi-dimensional solitons which are localized in both
space and time. We show that such solitons exist in two- and three-dimensional
self-induced-transparency media and that they are fully stable. Our approximate
analytical calculation, backed and verified by direct numerical simulations,
yields the multi-dimensional generalization of the one-dimensional Sine-Gordon
soliton.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let
The Origin of Galactic Cosmic Rays
Motivated by recent measurements of the major components of the cosmic
radiation around 10 TeV/nucleon and above, we discuss the phenomenology of a
model in which there are two distinct kinds of cosmic ray accelerators in the
galaxy. Comparison of the spectra of hydrogen and helium up to 100 TeV per
nucleon suggests that these two elements do not have the same spectrum of
magnetic rigidity over this entire region and that these two dominant elements
therefore receive contributions from different sources.Comment: To be published in Physical Review D, 13 pages, with 3 figures,
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