3,184 research outputs found
Polarization qubit phase gate in driven atomic media
We present here an all--optical scheme for the experimental realization of a
quantum phase gate. It is based on the polarization degree of freedom of two
travelling single photon wave-packets and exploits giant Kerr nonlinearities
that can be attained in coherently driven ultracold atomic media.Comment: 4 pages, 1 figure, in press on PR
Slow Light amplification in a non-inverted gain medium
We investigate the propagation of a coherent probe light pulse through a
three-level atomic medium (in the --configuration) in the presence of
a pump laser under the conditions for gain without inversion. When the carrier
frequency of the probe pulse and the pump laser are in a Raman configuration,
we show that it is possible to amplify a slow propagating pulse. We also
analyze the regime in which the probe pulse is slightly detuned from resonance
where we observe anomalous light propagation.Comment: 7 pages, 10 figures. To be published in Europhysics Letter
Alluvial gravel sedimentation in a contractional growth fold setting, Sant Llorenc de Morunys, southeastern Pyrenees
This paper is included in the Special Publication entitled 'Cenozoic foreland basins of Western Europe' edited by A. Mascle, C. Puigdefabregas, H.P. Luterbacher and M. Fernandez. New data are presented on the classic growth structure at Sant Llorenc de Morunys (NE Ebro Basin, Spain). During the late Eocene to Oligocene thick alluvial-fan gravel sediments accumulated principally by repetitive sub-aerial mass flow (cohesionless debris flow and fluidal sediment flow) events, with smaller volumes of fan-stream flows. Subaerial, high-viscosity (cohesive) debris flows contributed comparatively small volumes of sediment to the succession. These sediments constructed a complex architecture of conglomeratic and sandstone-bearing lithosomes that were affected by stratal thickening and erosion across a growth fold pair and genetically related internal unconformities, which formed a long-lived thrust-related structure in the immediate footwall of the SE Pyrenean mountain front. Four periods of evolution for the Sant Llorenc growth structure are defined on the basis of distintive stratigraphical architecture. These describe a gross evolution from onlapping to overlapping growth strata, related to the ultimate demise of growth folding. In detail complex erosional and offlapping events punctuated the growth history, which shows extreme variation parallel to the axis of the structure. Patterns of palaeoflow were highly complex, showing distinct axial and transverse directions relatable to growth fold evolutionary periods. Palaeocurrents are considered to have been deflected and diverted by surficial differential subsidence and areas of relative uplift and erosion generated by fold growth. The complexity of sediment dispersal is compounded by variables intrinsic to alluvial fan environments. The Sant Llorenc de Morunys growth strata provide information on how sediments are reorganized by syndepositionally-growing structures and on the nature of sediment distribution between external fold-and-thrust belts and foreland basins
Transverse Fresnel-Fizeau drag effects in strongly dispersive media
A light beam normally incident upon an uniformly moving dielectric medium is
in general subject to bendings due to a transverse Fresnel-Fizeau light drag
effect. In conventional dielectrics, the magnitude of this bending effect is
very small and hard to detect. Yet, it can be dramatically enhanced in strongly
dispersive media where slow group velocities in the m/s range have been
recently observed taking advantage of the electromagnetically induced
transparency (EIT) effect. In addition to the usual downstream drag that takes
place for positive group velocities, we predict a significant anomalous
upstream drag to occur for small and negative group velocities. Furthermore,
for sufficiently fast speeds of the medium, higher order dispersion terms are
found to play an important role and to be responsible for peculiar effects such
as light propagation along curved paths and the restoration of the spatial
coherence of an incident noisy beam. The physics underlying this new class of
slow-light effects is thoroughly discussed
Polarization phase gate with a tripod atomic system
We analyze the nonlinear optical response of a four-level atomic system
driven into a tripod configuration. The large cross-Kerr nonlinearities that
occurr in such a system are shown to produce nonlinear phase shift of order
. Such a substantial shift may be observed in a cold atomic gas in a
magneto-optical trap where it coupl be fasibly exploited towards the
realization of a polarization quantum phase gate. The experimental feasibility
of such a gate is here examined in detail.Comment: Corrected versio
Shelf Life Extension and Nutritional Quality Preservation of Sour Cherries through High Pressure Processing
The present study assessed the effectiveness of high pressure processing (HPP) for the quality maintenance of pitted sour cherries, with special regard to microbial stabilization and the maintenance of color and of chemical–nutritional properties. The HPP treatment (600 MPa for 3 min at 4 °C) was effective at minimizing the initial microbial load, which remained at negligible levels throughout 5 months of refrigerated storage. The color and total phytochemical content of sour cherries were not influenced by the HPP treatment and were maintained at levels comparable with the fresh product for 3 months of refrigerated storage. For longer storage periods, the typical red color decreased, in agreement with the content of total anthocyanins, which showed a significant decrease (up to 65% after 5 months). The antioxidant activity, measured by the ABTS and DPPH assays, was not affected by the HPP treatment, but slightly reduced during refrigerated storage. The study suggests that HPP may be exploited to extend the shelf life, while maintaining the fresh-like features of sour cherries, thus offering an alternative option to current preservation techniques (based on freezing or heating) commonly applied to this product
Preliminary molecular phylogeny for Galerucinae sensu lato (Coleoptera: Chrysomelidae) based on rRNA gene for Large Subunit 28S with emphasis on Neotropical species.
Statistics of Raman-Active Excitations via Masurement of Stokes-Anti-Stokes Correlations
A general fundamental relation connecting the correlation of Stokes and
anti-Stokes modes to the quantum statistical behavior of vibration and pump
modes in Raman-active materials is derived. We show that under certain
conditions this relation can be used to determine the equilibrium number
variance of phonons.Time and temperature ranges for which such conditions can
be satisfied are studied and found to be available in todays' experimental
standards. Furthermore, we examine the results in the presence of multi-mode
pump as well as for the coupling of pump to the many vibration modes and
discuss their validity in these cases.Comment: 12 pages, 1 figure, accepted for publication in Phys.Rev.
Slow group velocity and Cherenkov radiation
We theoretically study the effect of ultraslow group velocities on the
emission of Vavilov-Cherenkov radiation in a coherently driven medium. We show
that in this case the aperture of the group cone on which the intensity of the
radiation peaks is much smaller than that of the usual wave cone associated
with the Cherenkov coherence condition. We show that such a singular behaviour
may be observed in a coherently driven ultracold atomic gas.Comment: 4 pages, 4 figure
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