5,089 research outputs found
Self-trapping of light and nonlinear localized modes in 2D photonic crystals and waveguides
We overview our recent results on the nonlinear localized modes in
two-dimensional (2D) photonic crystals and photonic-crystal waveguides.
Employing the technique based on the Green function, we describe the existence
domains for nonlinear guided modes in photonic crystal waveguides and study
their unique properties including bistability. We also show that low-amplitude
nonlinear modes near the band edge of a reduced-symmetry 2D square-lattice
photonic crystals, which are usually unstable, can be stabilized due to
effective long-range linear and nonlinear interactions.Comment: 20 pages (LaTeX) with 12 figures (EPS
The Extent of Multi-particle Quantum Non-locality
It is well known that entangled quantum states can be nonlocal: the
correlations between local measurements carried out on these states cannot
always be reproduced by local hidden variable models. Svetlichny, followed by
others, showed that multipartite quantum states are even more nonlocal than
bipartite ones in the sense that nonlocal classical models with (super-luminal)
communication between some of the parties cannot reproduce the quantum
correlations. Here we study in detail the kinds of nonlocality present in
quantum states. More precisely we enquire what kinds of classical communication
patterns cannot reproduce quantum correlations. By studying the extremal points
of the space of all multiparty probability distributions, in which all parties
can make one of a pair of measurements each with two possible outcomes, we find
a necessary condition for classical nonlocal models to reproduce the statistics
of all quantum states. This condition extends and generalises work of
Svetlichny and others in which it was shown that a particular class of
classical nonlocal models, the ``separable'' models, cannot reproduce the
statistics of all multiparticle quantum states. Our condition shows that the
nonlocality present in some entangled multiparticle quantum states is much
stronger than previously thought. We also study the sufficiency of our
condition.Comment: 10 pages, 2 figures, journal versio
Cost-Effective HITs for Relative Similarity Comparisons
Similarity comparisons of the form "Is object a more similar to b than to c?"
are useful for computer vision and machine learning applications.
Unfortunately, an embedding of points is specified by triplets,
making collecting every triplet an expensive task. In noticing this difficulty,
other researchers have investigated more intelligent triplet sampling
techniques, but they do not study their effectiveness or their potential
drawbacks. Although it is important to reduce the number of collected triplets,
it is also important to understand how best to display a triplet collection
task to a user. In this work we explore an alternative display for collecting
triplets and analyze the monetary cost and speed of the display. We propose
best practices for creating cost effective human intelligence tasks for
collecting triplets. We show that rather than changing the sampling algorithm,
simple changes to the crowdsourcing UI can lead to much higher quality
embeddings. We also provide a dataset as well as the labels collected from
crowd workers.Comment: 7 pages, 7 figure
Levinson's theorem for Schroedinger operators with point interaction: a topological approach
In this note Levinson theorems for Schroedinger operators in R^n with one
point interaction at 0 are derived using the concept of winding numbers. These
results are based on new expressions for the associated wave operators.Comment: 7 page
Comment on "Demonstration of the Casimir Force in the 0.6 to 6 micrometer Range"
We comment on a recently published measurement of the Casimir force for
distances in the 0.6 to 6 micrometer range between two Au surfaces (Phys. Rev.
Lett. 78, 5(1997)) and the net discrepancy reported for the comparison with
theoretical predictions (Phys. Rev. Lett. 81, 5475 (1998)).Comment: 1 page, LaTeX, 2 encapsulated postscript figure
The Kondo effect in bosonic spin liquids
In a metal, a magnetic impurity is fully screened by the conduction electrons
at low temperature. In contrast, impurity moments coupled to spin-1 bulk
bosons, such as triplet excitations in paramagnets, are only partially
screened, even at the bulk quantum critical point. We argue that this
difference is not due to the quantum statistics of the host particles but
instead related to the structure of the impurity-host coupling, by
demonstrating that frustrated magnets with bosonic spinon excitations can
display a bosonic version of the Kondo effect. However, the Bose statistics of
the bulk implies distinct behavior, such as a weak-coupling impurity quantum
phase transition, and perfect screening for a range of impurity spin values. We
discuss implications of our results for the compound Cs2CuCl4, as well as
possible extensions to multicomponent bosonic gases.Comment: 4 pages, 3 figures. The weak coupling RG flow was corrected and
expanded in last versio
Formation of quasi-free and bubble positronium states in water and aqueous solutions
It is shown that in aqueous solutions a positronium atom is first formed in
the quasi-free state, and, after 50-100 ps, becomes localized in a nanobubble.
Analysis of the annihilation spectra of NaNO3 aqueous solutions shows that the
hydrated electron is not involved in the positronium (Ps) formation
Deux ou trois choses que l'on savait dans la France de l'Ouest, en 2001, a propos de la nature de certaines structures funéraires dites monumentales, ainsi que leur ordonnancement chronologique au long des Ve et IVe millenaires
On donne ici des résultats récents sur les monuments mégalithiques du Morbihan (site de
Lannec Er Gadouer), et quelques idées sur la monumentalité funéraire et le Néolithique des régiones atlantiques
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