213 research outputs found
On the propagation of an optical wave in a photorefractive medium
The aim of this paper is first to review the derivation of a model describing
the propagation of an optical wave in a photorefractive medium and to present
various mathematical results on this model: Cauchy problem, solitary waves
From Bloch model to the rate equations II: the case of almost degenerate energy levels
Bloch equations give a quantum description of the coupling between an atom
and a driving electric force. In this article, we address the asymptotics of
these equations for high frequency electric fields, in a weakly coupled regime.
We prove the convergence towards rate equations (i.e. linear Boltzmann
equations, describing the transitions between energy levels of the atom). We
give an explicit form for the transition rates. This has already been performed
in [BFCD03] in the case when the energy levels are fixed, and for different
classes of electric fields: quasi or almost periodic, KBM, or with continuous
spectrum. Here, we extend the study to the case when energy levels are possibly
almost degenerate. However, we need to restrict to quasiperiodic forcings. The
techniques used stem from manipulations on the density matrix and the averaging
theory for ordinary differential equations. Possibly perturbed small divisor
estimates play a key role in the analysis. In the case of a finite number of
energy levels, we also precisely analyze the initial time-layer in the rate
aquation, as well as the long-time convergence towards equilibrium. We give
hints and counterexamples in the infinite dimensional case
Cooling Tests of the NectarCAM camera for the Cherenkov Telescope Array
The NectarCAM is a camera proposed for the medium-sized telescopes in the
framework of the Cherenkov Telescope Array (CTA), the next-generation
observatory for very-high-energy gamma-ray astronomy. The cameras are designed
to operate in an open environment and their mechanics must provide protection
for all their components under the conditions defined for the CTA observatory.
In order to operate in a stable environment and ensure the best physics
performance, each NectarCAM will be enclosed in a slightly overpressurized,
nearly air-tight, camera body, to prevent dust and water from entering. The
total power dissipation will be ~7.7 kW for a 1855-pixel camera. The largest
fraction is dissipated by the readout electronics in the modules. We present
the design and implementation of the cooling system together with the test
bench results obtained on the NectarCAM thermal demonstrator.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherlands. All CTA contributions at
arXiv:1508.0589
The Wide-Field X and Gamma-Ray Telescope ECLAIRs aboard the Gamma-Ray Burst Multi-Wavelength Space Mission SVOM
The X and Gamma-ray telescope ECLAIRs is foreseen to be launched on a low
Earth orbit (h=630 km, i=30 degrees) aboard the SVOM satellite (Space-based
multi-band astronomical Variable Objects Monitor), a French-Chinese mission
with Italian contribution. Observations are expected to start in 2013. It has
been designed to detect and localize Gamma-Ray Bursts (GRBs) or persistent
sources of the sky, thanks to its wide field of view (about 2 sr) and its
remarkable sensitivity in the 4-250 keV energy range, with enhanced imaging
sensitivity in the 4-70 keV energy band. These characteristics are well suited
to detect highly redshifted GRBs, and consequently to provide fast and accurate
triggers to other onboard or ground-based instruments able to follow-up the
detected events in a very short time from the optical wavelength bands up to
the few MeV Gamma-Ray domain.Comment: Proccedings of the "2008 Nanjing GRB Conference", June 23-27 2008,
Nanjing, Chin
Etude spectrale de l'échantillonnage par traversée de niveaux
La tendance actuelle en microélectronique est d'intégrer des systèmes complexes sur une seule puce (« SoC » pour Sytems on chip): capteur, convertisseur analogique-numérique (CAN), traitement numérique du signal, transmission de données. Ces systèmes doivent être peu coûteux, de taille réduite, faible bruit et surtout peu consommateur d'énergie parce qu'il sont souvent alimentés par batteries. Parmi les étages cités, les CAN sont les plus difficiles à concevoir dans le respect du cahier des charges. Dans cette perspective, une nouvelle classe de convertisseur a été développée à partir de l'association de la technologie asynchrone et de l'échantillonnage non uniforme par traversée de niveaux. Le schéma d'échantillonnage est analysé pour les signaux périodiques mettant en évidence un repliement de spectre. Cependant l'étude de la reconstruction montre qu'un signal peut être reconstruit grâce à l'information portée par les intervalles de temps et ce malgré le repliement
Quantum microwave parametric interferometer
Classical interferometers are indispensable tools for the precise
determination of various physical quantities. Their accuracy is bound by the
standard quantum limit. This limit can be overcome by using quantum states or
nonlinear quantum elements. Here, we present the experimental study of a
nonlinear Josephson interferometer operating in the microwave regime. Our
quantum microwave parametric interferometer (QUMPI) is based on superconducting
flux-driven Josephson parametric amplifiers combined with linear microwave
elements. We perform a systematic analysis of the implemented QUMPI. We find
that its Gaussian interferometric power exceeds the shot-noise limit and
observe sub-Poissonian photon statistics in the output modes. Furthermore, we
identify a low-gain operation regime of the QUMPI which is essential for
optimal quantum measurements in quantum illumination protocols.Comment: 6 pages, 5 figure
Demonstration of microwave single-shot quantum key distribution
Security of modern classical data encryption often relies on computationally
hard problems, which can be trivialized with the advent of quantum computers. A
potential remedy for this is quantum communication which takes advantage of the
laws of quantum physics to provide secure exchange of information. Here,
quantum key distribution (QKD) represents a powerful tool, allowing for
unconditionally secure quantum communication between remote parties. At the
same time, microwave quantum communication is set to play an important role in
future quantum networks because of its natural frequency compatibility with
superconducting quantum processors and modern near-distance communication
standards. To this end, we present an experimental realization of a
continuous-variable QKD protocol based on propagating displaced squeezed
microwave states. We use superconducting parametric devices for generation and
single-shot quadrature detection of these states. We demonstrate unconditional
security in our experimental microwave QKD setting. We show that security
performance can be improved by adding finite trusted noise to the preparation
side. Our results indicate feasibility of secure microwave quantum
communication with the currently available technology in both open-air (up to
80 m) and cryogenic (over 1000 m) conditions.Comment: 9 pages, 3 figures, 1 supplementary information fil
Measurement of the response of heat-and-ionization germanium detectors to nuclear recoils
The heat quenching factor Q' (the ratio of the heat signals produced by
nuclear and electron recoils of equal energy) of the heat-and-ionization
germanium bolometers used by the EDELWEISS collaboration has been measured. It
is explained how this factor affects the energy scale and the effective
quenching factor observed in calibrations with neutron sources. This effective
quenching effect is found to be equal to Q/Q', where Q is the quenching factor
of the ionization yield. To measure Q', a precise EDELWEISS measurement of Q/Q'
is combined with values of Q obtained from a review of all available
measurements of this quantity in tagged neutron beam experiments. The
systematic uncertainties associated with this method to evaluate Q' are
discussed in detail. For recoil energies between 20 and 100 keV, the resulting
heat quenching factor is Q' = 0.91+-0.03+-0.04, where the two errors are the
contributions from the Q and Q/Q' measurements, respectively. The present
compilation of Q values and evaluation of Q' represent one of the most precise
determinations of the absolute energy scale for any detector used in direct
searches for dark matter.Comment: 28 pages, 7 figures. Submitted to Phys. Rev.
Identification of backgrounds in the EDELWEISS-I dark matter search experiment
This paper presents our interpretation and understanding of the different
backgrounds in the EDELWEISS-I data sets. We analyze in detail the several
populations observed, which include gammas, alphas, neutrons, thermal sensor
events and surface events, and try to combine all data sets to provide a
coherent picture of the nature and localisation of the background sources. In
light of this interpretation, we draw conclusions regarding the background
suppression scheme for the EDELWEISS-II phase
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