4,757 research outputs found
Heralded single-photon generation using imperfect single-photon sources and a two-photon-absorbing medium
We propose a setup for a heralded, i.e. announced generation of a pure
single-photon state given two imperfect sources whose outputs are represented
by mixtures of the single-photon Fock state with the vacuum
. Our purification scheme uses beam splitters, photodetection and a
two-photon-absorbing medium. The admixture of the vacuum is fully eliminated.
We discuss two potential realizations of the scheme.Comment: 22 pages, 8 figures (LaTeX). In version v2 we have slightly modified
our setup so as to increase the success probability of single-photon
generation by a factor of two. In addition, in an appendix we discuss
alternative realizations of single-photon generation without a Mach-Zehnder
interferometer. Three new figures have been added. Version v3 is a revised
version published in Phys. Rev. A. It contains numerous minor corrections and
clarifications. A new figure has been added in order to clarify our
convention regarding labelling the field modes. The action of the beam
splitters in the Schroedinger picture is introduced. A new reference has been
include
Annotation of Heterogenous Media Using OntoMedia
While ontologies exist for the annotation of monomedia, interoperability between these schemes is an important issue. The OntoMedia ontology consists of a generic core, capable of representing a diverse range of media, as well as extension ontologies to focus on specific formats. This paper provides an overview of the OntoMedia ontologies, together with a detailed case study when applied to video, a scripted form, and an associated short story
Chronic cough is associated with long breaks in esophageal peristaltic integrity on high-resolution manometry
Saffman-Taylor fingers with kinetic undercooling
The mathematical model of a steadily propagating Saffman-Taylor finger in a
Hele-Shaw channel has applications to two-dimensional interacting streamer
discharges which are aligned in a periodic array. In the streamer context, the
relevant regularisation on the interface is not provided by surface tension,
but instead has been postulated to involve a mechanism equivalent to kinetic
undercooling, which acts to penalise high velocities and prevent blow-up of the
unregularised solution. Previous asymptotic results for the Hele-Shaw finger
problem with kinetic undercooling suggest that for a given value of the kinetic
undercooling parameter, there is a discrete set of possible finger shapes, each
analytic at the nose and occupying a different fraction of the channel width.
In the limit in which the kinetic undercooling parameter vanishes, the fraction
for each family approaches 1/2, suggesting that this 'selection' of 1/2 by
kinetic undercooling is qualitatively similar to the well-known analogue with
surface tension. We treat the numerical problem of computing these
Saffman-Taylor fingers with kinetic undercooling, which turns out to be more
subtle than the analogue with surface tension, since kinetic undercooling
permits finger shapes which are corner-free but not analytic. We provide
numerical evidence for the selection mechanism by setting up a problem with
both kinetic undercooling and surface tension, and numerically taking the limit
that the surface tension vanishes.Comment: 10 pages, 6 figures, accepted for publication by Physical Review
Priority setting and health policy and systems research
Health policy and systems research (HPSR) has been identified as critical to scaling-up interventions to achieve the millennium development goals, but research priority setting exercises often do not address HPSR well. This paper aims to (i) assess current priority setting methods and the extent to which they adequately include HPSR and (ii) draw lessons regarding how HPSR priority setting can be enhanced to promote relevant HPSR, and to strengthen developing country leadership of research agendas
Indeterminate-length quantum coding
The quantum analogues of classical variable-length codes are
indeterminate-length quantum codes, in which codewords may exist in
superpositions of different lengths. This paper explores some of their
properties. The length observable for such codes is governed by a quantum
version of the Kraft-McMillan inequality. Indeterminate-length quantum codes
also provide an alternate approach to quantum data compression.Comment: 32 page
On-demand single-photon state generation via nonlinear absorption
We propose a method for producing on-demand single-photon states based on
collision-induced exchanges of photons and unbalanced linear absorption between
two single-mode light fields. These two effects result in an effective
nonlinear absorption of photons in one of the modes, which can lead to single
photon states. A quantum nonlinear attenuator based on such a mechanism can
absorb photons in a normal input light pulse and terminate the absorption at a
single-photon state. Because the output light pulses containing single photons
preserve the properties of the input pulses, we expect this method to be a
means for building a highly controllable single photon source.Comment: 5 pages, 2 figures, to appear in PRA. To be published in PR
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