2,427 research outputs found
Unconditional security proof of long-distance continuous-variable quantum key distribution with discrete modulation
We present a continuous-variable quantum key distribution protocol combining
a discrete modulation and reverse reconciliation. This protocol is proven
unconditionally secure and allows the distribution of secret keys over long
distances, thanks to a reverse reconciliation scheme efficient at very low
signal-to-noise ratio.Comment: 4 pages, 2 figure
The Reduction in theWorking Week from 1997 to 2003: The Construction of the Aubry Acts and Preliminary Evaluations
The Aubry acts combine a sharp legislative reduction in the legal working week with a sector and corporate bargaining incentive based on a two-step mechanism. In June 1998, the first act set a new legal working week norm and introduced an incentive scheme to provide assistance to firms that made the transition before some deadlines and created or kept jobs. It is not easy to make a short-run evaluation of the Aubry acts. They appear to have had a certain amount of short-run employment success with the creation of some 350,000 jobs. For employers, the introduction of the shorter working week provided an opportunity to introduce or increase flexibility. This moreover had an effect on some of the employees working conditions. Both the quantitative and qualitative studies tend to find an increase in labour inequalities among employees: between socio-economic groups, status and age brackets, and between firms and sectors.Working Time Reduction, Collective Bargaining, Working Time Flexibility, Aubry Laws Development, Aubry Laws Results
Orbital angular momentum bistability in a microlaser
Light's orbital angular momentum (OAM) is an unbounded degree of freedom
emerging in helical beams that appears very advantageous technologically. Using
a chiral microlaser, i.e. an integrated device that allows generating an
emission carrying a net OAM, we demonstrate a regime of bistability involving
two modes presenting distinct OAM (L = 0 and L = 2). Furthermore, thanks to an
engineered spin-orbit coupling of light in the device, these modes also exhibit
distinct polarization patterns, i.e. cirular and azimuthal polarizations. Using
a dynamical model of rate euqations, we show that this bistability arises from
polarization-dependent saturation of the gain medium. Such a bistable regime
appears very promising for implementing ultrafast optical switches based on the
OAM of light. As well, it paves the way to the exploration of dynamical
processes involving phase and polarization vortices
Sub-Doppler optical resolution by confining a vapour in a nanostructure
We show that a thermal vapor confined in a nanostructure is of spectroscopic
interest. We perform reflection spectroscopy on a Cs vapour cell whose window
is covered with a thin opal film (typically, 10 or 20 layers of ~ 1{\mu}m
diameter spheres). Sub-Doppler structures appear in the optical spectrum in a
purely linear regime of optical excitation and the signal is shown to originate
from the interstitial regions of the opal. These narrow spectral structures,
observable for a large range of oblique incidence angles (~ 30-50°), are an
original feature associated to the 3-D vapor confinement. It remembers a Dicke
narrowing, i.e. a Doppler broadening suppression when the atomic motion is
sub-wavelength confined. This narrowing, commonly observed in the r.f. domain
when a buffer gas ensures a collision confinement effect, had remained elusive
in the optical frequency. Also, we describe preliminary experiments performed
in a pump-probe technique, intended to elucidate the spatial origin of the
narrow contribution. We finally discuss how our results allow envisioning
micron-size references for optical frequency clocks, and high resolution
spectroscopy of weak and hard-to-saturate molecular lines
Thermodynamics of hydration of MX80-Na: an experimental study of the hydration energies
Hydration properties of swelling clay minerals may be very variable depending on the chemical composition of the clay, on the nature of the interlayer cations and on the interlayer charge (Berend et al., 1995; Vieillard et al., 2011). The Wyoming smectite has been largely studied, notably for assessing its hydration behavior as a function of the interlayer cations, in connection with its structural characteristics (Ferrage et al., 2005; Salles et al., 2007). In the present work, carried out as part of a collaborative Andra/BRGM/HydrASA research program for ThermoChimie project, we propose an original experimental study, based on adsorption and desorption isotherms performed on MX80 clay samples. The goal is to determine energetic contributions to the reactions of hydration, which have been revealed to be non-negligible with respect to the stability of the clay minerals (Gailhanou et al., submitted). In particular, the present work addresses the problems of the hysteresis loop between adsorption and desorption isotherms and of the irreversibility of hydration reactions. This is directly related to the application of classical thermodynamics to the hydration reactions of clay minerals. In a first stage, an experimental study is dedicated to better understand the origin of the hysteresis loop which is systematically observed for the adsorption-desorption isotherms at 25°C. The development of the hysteresis loop has been studied by considering several kinetically related parameters: stabilization periods, temperatures (from 25°C to 60°C) and hydration steps (Figure 1). No sensible change was observed in the hysteresis loop. Therefore, the amount of adsorbed water depends on the followed reaction pathway (adsorption or desorption). The variations in microstructures and in the distribution of hydration layers (0/1/2 water layers; Ferrage et al., 2005) as a function of relative humidity (RH) could provide a possible explanation for this phenomenon
Polariton-polariton interaction potentials determination by pump-probe degenerate scattering in a multiple microcavity
International audienceWe study the polarisation-dependent polariton-polariton interaction through its effect on a parametric scattering process in a microcavity (MC). The ratio of the anti-circular interaction strength V2 over its co-circular counterpart V1 is involved in defining the regime in which many nonlinear processes arise in MCs, such as parametric conversion or condensation. We measure the ratio V2/V1 using a stimulated energy-degenerate parametric scattering process in a multiple MC. The sample is pumped at normal incidence, probed with a non-zero angle, and the phase-matched idler is observed at the opposite angle. The idler behaviour, both in power and polarisation, is compared to a hamiltonian interaction model that takes into account the two polarisation-dependent parametric scattering channels characterized by V1 and V2. The proposed method to measure the ratio V2/V1 is convenient and precise. The flexibility of the triple MC allows to observe the process and measure this ratio over a large range of detunings, where we find it to be highly dependent on the detuning. These measurements complement the previous study of Vladimirova et al. [Phys. Rev. B 82, 075301 (2010)] with an original approach and for detunings that were unexplored up to now
Infiltrating a thin or single layer opal with an atomic vapour: sub-doppler signals and crystal optics
Artificial thin glass opals can be infiltrated with a resonant alkali-metal
vapour, providing novel types of hybrid systems. The reflection at the
interface between the substrate and the opal yields a resonant signal, which
exhibits sub-Doppler structures in linear spectroscopy for a range of oblique
incidences. This result is suspected to originate in an effect of the
three-dimensional confinement of the vapour in the opal interstices. It is here
extended to a situation where the opal is limited to a few or even a single
layer opal film, which is a kind of bidimensional grating. We have developed a
flexible one-dimensional layered optical model, well suited for a
Langmuir-Blodgett opal. Once extended to the case of a resonant infiltration,
the model reproduces quick variations of the lineshape with incidence angle or
polarization. Alternately, for an opal limited to a single layer of identical
spheres, a three-dimensional numerical calculation was developed. It predicts
crystalline anisotropy, which is demonstrated through diffraction on an empty
opal made of a single-layer of polystyrene spheres.Comment: to appear in Europhysics Letters, Special Issue (Proceedings of META
14-Singapore May 2014
Three-dimensional confinement of vapor in nanostructures for sub-Doppler optical resolution
International audienceWe confine a Cs thermal vapor in the interstitial regions of a glass opal. We perform linear reflection spectroscopy on a cell whose window is covered with a thin film (10 or 20 layers) of 1000 nm (or 400 nm) diameter glass spheres and observe sub-Doppler structures in the optical spectrum for a large range of oblique incidences. This original feature associated with the inner (3-dimensional) confinement of the vapor in the interstitial regions of the opal evokes a Dicke narrowing. We finally consider possible micron-size references for optical frequency clocks based on weak, hard to saturate, molecular line
- …