Compensating fictitious magnetic field gradients in optical microtraps by using elliptically polarized dipole light

Tightly focused optical dipole traps induce vector light shifts ("fictitious magnetic fields") which complicate their use for single-atom trapping and manipulation. The problem can be mitigated by adding a larger, real magnetic field, but this solution is not always applicable; in particular, it precludes fast switching to a field-free configuration. Here we show that this issue can be addressed elegantly by deliberately adding a small elliptical polarization component to the dipole beam. In our experiments with single $^{87}$Rb atoms in a chopped trap, we observe improvements up to a factor 11 of the trap lifetime compared to the standard, seemingly ideal linear polarization. This effect results from a modification of heating processes via spin-state diffusion in state-dependent trapping potentials. We develop Monte-Carlo simulations of the evolution of the atom's internal and motional states and find that they agree quantitatively with the experimental data. The method is general and can be applied in all experiments where the longitudinal polarization component is non-negligible.Comment: 6 pages, 5 figure

Bond Liquidity Premia

Recent asset pricing models of limits to arbitrage emphasize the role of funding conditions faced by financial intermediaries. In the US, the repo market is the key funding market. Then, the premium of on-the-run U.S. Treasury bonds should share a common component with risk premia in other markets. This observation leads to the following identification strategy. We measure the value of funding liquidity from the cross-section of on-the-run premia by adding a liquidity factor to an arbitrage-free term structure model. As predicted, we find that funding liquidity explains the cross-section of risk premia. An increase in the value of liquidity predicts lower risk premia for on-the-run and off-the-run bonds but higher risk premia on LIBOR loans, swap contracts and corporate bonds. Moreover, the impact is large and pervasive through crisis and normal times. We check the interpretation of the liquidity factor. It varies with transaction costs, S&P500 valuation ratios and aggregate uncertainty. More importantly, the liquidity factor varies with narrow measures of monetary aggregates and measures of bank reserves. Overall, the results suggest that different securities serve, in part, and to varying degrees, to fulfill investors' uncertain future needs for cash depending on the ability of intermediaries to provide immediacy.Financial markets; Financial stability

Overlapping two standing-waves in a microcavity for a multi-atom photon interface

We develop a light-matter interface enabling strong and uniform coupling between a chain of cold atoms and photons of an optical cavity. This interface is a fiber Fabry-Perot cavity, doubly resonant for both the wavelength of the atomic transition and for a geometrically commensurate red-detuned intracavity trapping lattice. Fulfilling the condition of a strong and uniform atom-photon coupling requires optimization of the spatial overlap between the two standing waves in the cavity. In a strong-coupling cavity, where the mode waists and Rayleigh range are small, we derive the expression of the optimal trapping wavelength taking into account the Gouy phase. The main parameter controlling the overlap of the standing waves is the relative phase shift at the reflection on the cavity mirrors between the two wavelengths, for which we derive the optimal value. We have built a microcavity optimized according to these results, employing custom-made mirrors with engineered reflection phase for both wavelengths. We present a method to measure with high precision the relative phase shift at reflection, which allows us to determine the spatial overlap of the two modes in this cavity.Comment: 14 pages, 7 figure

Economie de la diarrhée virale bovine ( BVD) : une meta-analyse

La diarrhée virale bovine (BVD) est une maladie endémique et cosmopolite des ruminants. De nombreux pays ont mis en place des plans d’éradication. Plusieurs travaux de synthèse ont évalué les stratégies autours de cette maladie, mais aucune synthèse sur son évaluation économique n’est disponible à ce jour. L’objectif est de synthétiser les données sur le coût total de la BVD et la baisse de ce coût lors de la mise en place de mesures de contrôle, grâce à deux méta-analyses.Les méta-analyses ont été conduites selon les procédures classiques. Les résultats des travaux sont particulièrement pertinents. Le coût annuel moyen par vache est évalué à 42,14 € (se=8,83). Ce coût est de 73,7 € lors d’une circulation virale débutant rapidement, intense et persistante. La vaccination et la biosécurité permettent une baisse du coût de la BVD, comparé à leur absence, de l’ordre de 8-13% et de 29-30% respectivement. Toutefois, l’effet des mesures de biosécurité et de vaccination sur le coût de la BVD est quasiment annulé par la présence de contacts avec des animaux tiers ou lors d’introduction d’animaux sans contrôle sanitaire préalable

Highly-efficient, diffraction-limited laser emission from a Vertical External Cavity Surface-emitting Organic Laser

We report on a solid-state laser structure being the organic counterpart of the Vertical External-Cavity Surface-Emitting Laser (VECSEL) design. The gain medium is a poly (methyl methacrylate) film doped with Rhodamine 640, spin-casted onto the High-Reflectivity mirror of a plano-concave resonator. Upon pumping by 7-ns pulses at 532 nm, a diffraction-limited beam (M^2=1) was obtained, with a conversion efficiency of 43%; higher peak powers (2kW) could be attained when resorting to shorter (0.5 ns) pump pulses. The spectrum was controlled by the thickness of the active layer playing the role of an intracavity etalon; tunability is demonstrated over up to 20 nm

EFFECTS OF ONE-HOUR ROAD RUNNING AND SHOE ON TIBIAL ACCELERATIONS IN RECREATIONAL RUNNERS

The purpose of this study was twofold. Firstly, we evaluated the effect of one-hour running on tibial acceleration parameters. Secondly, we determined whether the shoe fatigue after one-hour running would influence these tibial acceleration parameters. Ten runners ran at a constant preferred speed with a standard running shoe. They also ran one bout of 5 min with another identical but fresh running shoe before and after the one-hour run. Tibial acceleration amplitudes and wavelet analyses demonstrated a significant reduction of the tibial impact parameters after one-hour running, but no significant shoe effect. These reductions could be attributable to the slight increase in stride frequency from the beginning to the end of the one-hour running. Noteworthy, the tibial acceleration reduction was observable along the anteroposterior axis, not along the vertical axis. Considering the tibial acceleration as a potential risk factor for developing running-related injuries, these parameters did not change in a harmful way after one-hour of running at the preferred running speed. The shoe modification during the one-hour run did not seem to influence running biomechanics

Real time 3D US-tagging combined with 3D phase-based motion estimation

International audienceBy contrast with 2D imaging, quantitative analysis of 3D motion from ultrasound images can provide improved information in several applications, such as arterial mechanical assessment, heart motion and blood flow. Unfortunately, it remains difficult to obtain a high definition of the motion estimate in the lateral and elevation directions (i.e. perpendicular to the beam axis). To increase the definition in both these directions, this paper presents a 3D extension of a the transverse oscillations method that enables one to obtain ultrasound fields featuring oscillations along the 3 spatial dimensions, using a single apodization function. The 3D motion method is estimated using the phases of the images. Simulation results show that a 3D trajectory can be followed with a relative mean error smaller than 8%

Source localization and identification with a compact array of digital mems microphones

International audienceA compact microphone array was developed for source localization and identification. This planar array consists of an arrangement of 32 digital MEMS microphones, concentrated in an aperture of fewer than 10 centimeters, and connected to a computer by Ethernet (AVB protocol). 3D direction of arrival (DOA) localization is performed using the pressure and the particle velocity estimated at the center of the array. The pressure is estimated by averaging the signals of multiple microphones. We compare high order pressure finite differences to the Phase and Amplitude Gradient Estimation (PAGE) method for particle velocity estimation. This paper also aims at presenting a method for UAV detection using the developed sensor and supervised binary classification