Evolution of entanglement within classical light states

We investigate the evolution of quantum correlations over the lifetime of a multi-photon state. Measurements reveal time-dependent oscillations of the entanglement fidelity for photon pairs created by a single semiconductor quantum dot. The oscillations are attributed to the phase acquired in the intermediate, non-degenerate, exciton-photon state and are consistent with simulations. We conclude that emission of photon pairs by a typical quantum dot with finite polarisation splitting is in fact entangled in a time-evolving state, and not classically correlated as previously regarded

Practical security bounds against the Trojan-horse attack in quantum key distribution

In the quantum version of a Trojan-horse attack, photons are injected into the optical modules of a quantum key distribution system in an attempt to read information direct from the encoding devices. To stop the Trojan photons, the use of passive optical components has been suggested. However, to date, there is no quantitative bound that specifies such components in relation to the security of the system. Here, we turn the Trojan-horse attack into an information leakage problem. This allows us quantify the system security and relate it to the specification of the optical elements. The analysis is supported by the experimental characterization, within the operation regime, of reflectivity and transmission of the optical components most relevant to security.Comment: 18 pages, 11 figures. Some typos correcte

Improved fidelity of triggered entangled photons from single quantum dots

We demonstrate the on-demand emission of polarisation-entangled photon pairs from the biexciton cascade of a single InAs quantum dot embedded in a GaAs/AlAs planar microcavity. Improvements in the sample design blue shifts the wetting layer to reduce the contribution of background light in the measurements. Results presented show that >70% of the detected photon pairs are entangled. The high fidelity of the (|HxxHx>+|VxxVx>)/2^0.5 state that we determine is sufficient to satisfy numerous tests for entanglement. The improved quality of entanglement represents a significant step towards the realisation of a practical quantum dot source compatible with applications in quantum information.Comment: 9 pages. Paper is available free of charge at http://www.iop.org/EJ/abstract/1367-2630/8/2/029/, see also 'A semiconductor source of triggered entangled photon pairs', R. M. Stevenson et al., Nature 439, 179 (2006

Giant Stark effect in the emission of single semiconductor quantum dots

We study the quantum-confined Stark effect in single InAs/GaAs quantum dots embedded within a AlGaAs/GaAs/AlGaAs quantum well. By significantly increasing the barrier height we can observe emission from a dot at electric fields of -500 kV/cm, leading to Stark shifts of up to 25 meV. Our results suggest this technique may enable future applications that require self-assembled dots with transitions at the same energy

Epidemiology of glenohumeral dislocation and subsequent instability in an urban population

Background: Glenohumeral dislocation is the most commonly encountered adult joint instability. The epidemiology in the United Kingdom and worldwide is unclear and often limited to young, active groups that are not representative of general populations. Information regarding epidemiology and outcome from a first dislocation is useful for trauma service planning and patient counseling. We calculated the incidence of shoulder instability after a first dislocation in our urban population and investigated predictors of recurrent instability. Methods: A prospectively collected trauma database was retrospectively examined to identify patients with a first-time dislocation. Demographics, subsequent dislocation, and instability details were collected from electronic patient records. Results: In a 38-month study period, 329 first dislocations occurred in a population of 475,147 with mean follow-up 28.5 months (range, 10-50 months). The overall incidence for first-time dislocations in this population was 21.9 per 100,000 population, of which 7.9% sustained a redislocation and 6.1% had further symptomatic instability. There were 18.8% with associated greater tuberosity fractures, 8.8% sustained a nerve injury, and 2.7% were posterior dislocations. A bimodal distribution was observed for males (peak incidence per 100,000 of 42.1 and 50.9 in 15-24 and ≥85 age groups, respectively), and unimodal for females (peak 45.7 in the 65-74 age group). Conclusion: We demonstrate a previously unreported burden of dislocation in older age groups and suggest a rate of recurrence lower than previously reported in the United Kingdom. The group aged 15 to 19 years was at the highest risk of recurrent dislocation and instability. Gender was not a significant predictor of instability

The Effect of Land Albedo on the Climate of Land-Dominated Planets in the TRAPPIST-1 System

Variations in the reflective properties of the bulk material that comprises the surface of land-dominated planets will affect the planetary energy balance by interacting differently with incident radiation from the host star. Furthermore, low-mass cool stars, such as nearby M8V dwarf TRAPPIST-1, emit a significant fraction of their flux in longer wavelengths relative to the Sun in regions where terrestrial materials may exhibit additional variability in albedo. Using the Community Earth System Model (CESM) we investigate the effect of the composition of the land surface and its albedo on planetary climate in the context of spatially homogeneous, entirely land-covered planets with dry atmospheres at the orbital separation of TRAPPIST-1d, TRAPPIST-1e, and TRAPPIST-1f. We use empirically derived spectra of four terrestrial compositional endmembers (granite, calcite, aridisol, and dune sand) and a composite spectrum of TRAPPIST-1 for these simulations and compare these model output to an aquaplanet and several Sol-spectrum control cases. We report a difference of approximately 50 K in global mean surface temperature, variations in atmospheric rotational features, and a reduction in cross-equatorial heat transport between scenarios in which materials with higher albedo in the infrared (calcite and dune sand) were used and those with more absorptive crustal material, such as granite or dry soils. An aquaplanet TRAPPIST-1d scenario results in an unstable runaway greenhouse regime. Therefore, we demonstrate that determining the composition and albedo of continental landmasses is crucial for making accurate determinations of the climate of terrestrial exoplanets.Comment: 18 pages, 11 figures. Accepted for publication in the Astrophysical Journal (ApJ

Le secteur des télécommunications surfe-t-il de bulle en bulle ?

Le secteur des télécommunications a connu un développement rapide qui s’est accéléré à partir de la deuxième moitié des années 1990, avec l’apparition du GSM et de l’Internet. Mais la croissance réelle du secteur s’est rapidement transformée en une gigantesque bulle financière qui a été à l’origine de l’une des pires crises sectorielles qu’aient connu les économies modernes. Dans cet article, nous essayons d’identifier les facteurs qui ont conduit à une telle valorisation financière des entreprises de télécommunications ainsi que ceux qui ont conduit au retournement des marchés financiers. Enfin, à la veille de la mise en place de l’UMTS, certains éléments nous amènent à penser qu’une nouvelle bulle pourrait se former dans les années à venir. En annexes, nous simulons la rentabilité financière de l’UMTS et évaluons l’impact macroéconomique de ce projet sur les composantes de la croissance française.The telecommunication sector has recently undergone a fast development which accelerated from the second half of the 1990s, with the rise of the GSM and the Internet. But the actual growth of the sector turned into a gigantic financial bubble which was at the origin of one of the worst sector-based crises that the modern economies had seen. In this article, we try to identify the factors driving such a financial valuation of the telecommunications companies as well as those leading to the reversal of financial markets. Finally, on the verge of the implementation of the UMTS in France, some elements let us think that a new bubble might appear in the coming years. In the appendices, we simulate the financial profitability of the UMTS and estimate the macroeconomic impact of this project on the constituents of French economic growth