6,762 research outputs found
Accurate measurement of a 96% input coupling into a cavity using polarization tomography
Pillar microcavities are excellent light-matter interfaces providing an
electromagnetic confinement in small mode volumes with high quality factors.
They also allow the efficient injection and extraction of photons, into and
from the cavity, with potentially near-unity input and output-coupling
efficiencies. Optimizing the input and output coupling is essential, in
particular, in the development of solid-state quantum networks where artificial
atoms are manipulated with single incoming photons. Here we propose a technique
to accurately measure input and output coupling efficiencies using polarization
tomography of the light reflected by the cavity. We use the residual
birefringence of pillar microcavities to distinguish the light coupled to the
cavity from the uncoupled light: the former participates to rotating the
polarization of the reflected beam, while the latter decreases the polarization
purity. Applying this technique to a micropillar cavity, we measure a output coupling and a input coupling with unprecedented
precision.Comment: 6 pages, 3 figure
On cosmological observables in a swiss-cheese universe
Photon geodesics are calculated in a swiss-cheese model, where the cheese is
made of the usual Friedmann-Robertson-Walker solution and the holes are
constructed from a Lemaitre-Tolman-Bondi solution of Einstein's equations. The
observables on which we focus are the changes in the redshift, in the
angular-diameter--distance relation, in the luminosity-distance--redshift
relation, and in the corresponding distance modulus. We find that redshift
effects are suppressed when the hole is small because of a compensation effect
acting on the scale of half a hole resulting from the special case of spherical
symmetry. However, we find interesting effects in the calculation of the
angular distance: strong evolution of the inhomogeneities (as in the approach
to caustic formation) causes the photon path to deviate from that of the FRW
case. Therefore, the inhomogeneities are able to partly mimic the effects of a
dark-energy component. Our results also suggest that the nonlinear effects of
caustic formation in cold dark matter models may lead to interesting effects on
photon trajectories.Comment: 25 pages, 21 figures; replaced to fit the version accepted for
publication in Phys. Rev.
High energy photon interactions at the LHC
Experimental prospects for studying high-energy photon-photon and
photon-proton interactions at the CERN Large Hadron Collider (LHC) are
discussed. Cross sections are calculated for many electroweak and beyond the
Standard Model processes. Selection strategies based on photon interaction
tagging techniques are studied. Assuming a typical LHC multipurpose detector,
various signals and their irreducible backgrounds are presented after applying
acceptance cuts. Prospects are discussed for the Higgs boson search, detection
of supersymmetric particles and of anomalous quartic gauge couplings, as well
as for the top quark physics.Comment: 17 pages, 16 tables and 14 figure
Particulate barium tracing of significant mesopelagic carbon remineralisation in the North Atlantic
The remineralisation of sinking particles by prokaryotic heterotrophic activity is important for controlling oceanic carbon sequestration. Here, we report mesopelagic particulate organic carbon (POC) remineralisation fluxes in the North Atlantic along the GEOTRACES-GA01 section (GEOVIDE cruise; May-June 2014) using the particulate biogenic barium (excess barium; Baxs/ proxy. Important mesopelagic (100-1000 m) Baxs differences were observed along the transect depending on the intensity of past blooms, the phytoplankton community structure, and the physical forcing, including downwelling. The subpolar province was characterized by the highest mesopelagic Baxs content (up to 727 pmol L-1/, which was attributed to an intense bloom averaging 6 mg chl a m-3 between January and June 2014 and by an intense 1500m deep convection in the central Labrador Sea during the winter preceding the sampling. This downwelling could have promoted a deepening of the prokaryotic heterotrophic activity, increasing the Baxs content. In comparison, the temperate province, characterized by the lowest Baxs content (391 pmol L-1/, was sampled during the bloom period and phytoplankton appear to be dominated by small and calcifying species, such as coccolithophorids. The Baxs content, related to oxygen consumption, was converted into a remineralisation flux using an updated relationship, proposed for the first time in the North Atlantic. The estimated fluxes were of the same order of magnitude as other fluxes obtained using independent methods (moored sediment traps, incubations) in the North Atlantic. Interestingly, in the subpolar and subtropical provinces, mesopelagic POC remineralisation fluxes (up to 13 and 4.6 mmol Cm-2 d-1, respectively) were equalling and occasionally even exceeding upper-ocean POC export fluxes, deduced using the 234Th method. These results highlight the important impact of the mesopelagic remineralisation on the biological carbon pump of the studied area with a near-zero, deep (> 1000 m) carbon sequestration efficiency in spring 2014
Topological acoustics in coupled nanocavity arrays
The Su-Schrieffer-Heeger (SSH) model is likely the simplest one-dimensional
concept to study non-trivial topological phases and topological excitations.
Originally developed to explain the electric conductivity of polyacetylene, it
has become a platform for the study of topological effects in electronics,
photonics and ultra-cold atomic systems. Here, we propose an experimentally
feasible implementation of the SSH model based on coupled one-dimensional
acoustic nanoresonators working in the GHz-THz range. In this simulator it is
possible to implement different signs in the nearest neighbor interaction
terms, showing full tunability of all parameters in the SSH model. Based on
this concept we construct topological transition points generating nanophononic
edge and interface states and propose an easy scheme to experimentally probe
their spatial complex amplitude distribution directly by well-established
optical pump-probe techniques.Comment: 10 pages, 4 figure
Redshift spherical shell energy in isotropic Universes
We introduce the redshift spherical shell energy (RSSE), which can be used to
test in the redshift space the radial inhomogeneity of an isotropic universe,
providing additional constraints for LTB models, and a more general test of
cosmic homogeneity.Comment: 11 pages, 2 figures, Accepted by Physical Review D1
Senescence in natural populations of animals:Widespread evidence and its implications for bio-gerontology
That senescence is rarely, if ever, observed in natural populations is an oft-quoted fallacy within bio-gerontology. We identify the roots of this fallacy in the otherwise seminal works of Medawar and Comfort, and explain that under antagonistic pleiotropy or disposable soma explanations for the evolution of senescence there is no reason why senescence cannot evolve to be manifest within the life expectancies of wild organisms. The recent emergence of long-term field studies presents irrefutable evidence that senescence is commonly detected in nature. We found such evidence in 175 different animal species from 340 separate studies. Although the bulk of this evidence comes from birds and mammals, we also found evidence for senescence in other vertebrates and insects. We describe how high-quality longitudinal field data allow us to test evolutionary explanations for differences in senescence between the sexes and among traits and individuals. Recent studies indicate that genes, prior environment and investment in growth and reproduction influence aging rates in the wild. We argue that â with the fallacy that wild animals do not senesce finally dead and buried â collaborations between bio-gerontologists and field biologists can begin to test the ecological generality of purportedly âpublicâ mechanisms regulating aging in laboratory models
Formation of cosmological mass condensation within a FRW universe: exact general relativistic solutions
Within the framework of an exact general relativistic formulation of gluing
manifolds, we consider the problem of matching an inhomogeneous overdense
region to a Friedmann-Robertson-Walker background universe in the general
spherical symmetric case of pressure-free models. It is shown that, in general,
the matching is only possible through a thin shell, a fact ignored in the
literature. In addition to this, in subhorizon cases where the matching is
possible, an intermediate underdense region will necessarily arise.Comment: 6 page
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