Direct measurement of superluminal group velocity and of signal velocity in an optical fiber

We present an easy way of observing superluminal group velocities using a birefringent optical fiber and other standard devices. In the theoretical analysis, we show that the optical properties of the setup can be described using the notion of "weak value". The experiment shows that the group velocity can indeed exceed c in the fiber; and we report the first direct observation of the so-called "signal velocity", the speed at which information propagates and that cannot exceed c.Comment: 5 pages, 5 figure

Quantum key distribution and 1 Gbit/s data encryption over a single fibre

We perform quantum key distribution (QKD) in the presence of 4 classical channels in a C-band dense wavelength division multiplexing (DWDM) configuration using a commercial QKD system. The classical channels are used for key distillation and 1 Gbps encrypted communication, rendering the entire system independent from any other communication channel than a single dedicated fibre. We successfully distil secret keys over fibre spans of up to 50 km. The separation between quantum channel and nearest classical channel is only 200 GHz, while the classical channels are all separated by 100 GHz. In addition to that we discuss possible improvements and alternative configurations, for instance whether it is advantageous to choose the quantum channel at 1310 nm or to opt for a pure C-band configuration.Comment: 9 pages, 7 figure

Feasibility of free space quantum key distribution with coherent polarization states

We demonstrate for the first time the feasibility of free space quantum key distribution with continuous variables under real atmospheric conditions. More specifically, we transmit coherent polarization states over a 100m free space channel on the roof of our institute's building. In our scheme, signal and local oscillator are combined in a single spatial mode which auto-compensates atmospheric fluctuations and results in an excellent interference. Furthermore, the local oscillator acts as spatial and spectral filter thus allowing unrestrained daylight operation.Comment: 12 pages, 8 figures, extensions in sections 2, 3.1, 3.2 and 4. This is an author-created, un-copyedited version of an article accepted for publication in New Journal of Physics (Special Issue on Quantum Cryptography: Theory and Practice). IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from i

The Security of Practical Quantum Key Distribution

Quantum key distribution (QKD) is the first quantum information task to reach the level of mature technology, already fit for commercialization. It aims at the creation of a secret key between authorized partners connected by a quantum channel and a classical authenticated channel. The security of the key can in principle be guaranteed without putting any restriction on the eavesdropper's power. The first two sections provide a concise up-to-date review of QKD, biased toward the practical side. The rest of the paper presents the essential theoretical tools that have been developed to assess the security of the main experimental platforms (discrete variables, continuous variables and distributed-phase-reference protocols).Comment: Identical to the published version, up to cosmetic editorial change

Field test of quantum key distribution in the Tokyo QKD Network

A novel secure communication network with quantum key distribution in a metropolitan area is reported. Different QKD schemes are integrated to demonstrate secure TV conferencing over a distance of 45km, stable long-term operation, and application to secure mobile phones.Comment: 21 pages, 19 figure

La maladie de Preiser : Une série de cinq cas

Preiser's disease, or avascular necrosis of the scaphoid occurs without fracture or non-union. Between 1998 and 2009, the authors report on 5 patients who complained of mild pain on the radial aspect of the wrist, associated with stiffness and/or loss of strength. Our management consisted in different options: one bilateral intraarticular injection of hyaluronic acid, three vascularised radial bone graft and one resection of the first carpal row. With four and a half years follow-up, our results are quite satisfactory for improvement of pain, sometimes with residual postoperative stiffness. Management remains difficult because Preiser's disease is rare and there are no relevant prospective control studies. We attempt to provide an algorithm for early management of the disease and to answer the question: " until when can we save the scaphoid and how?" © 2012

Results of the modified Bunelli tenodesis for treatment of scapholunate instability: a retrospective study of 19 patients.

PURPOSE: Management of chronic scapholunate (SL) instability without osteoarthritis remains controversial. In order to recreate an SL interosseous linkage, some surgeons opt for a limited wrist arthrodesis, whereas others use soft tissue stabilization. The purpose of the current study was to review and assess the therapeutic benefit of the modified Brunelli tenodesis that used the flexor carpi radialis tendon to replicate the stabilizing ligaments of the scaphoid. METHODS: Between 2001 and 2005, 19 tenodesis procedures have been performed to correct dynamic or static SL instability without osteoarthritis. On average, patients had surgery 15 months after injury. The mean follow-up was 37 months. RESULTS: After surgery, 15 patients had no to mild pain with a mean visual analog scale score of 3 of 10. The average wrist motion was 50 degrees extension, 41 degrees flexion, 24 degrees radial deviation, and 29 degrees ulnar deviation (75%, 73%, 68%, and 86% of the uninvolved wrists, respectively). The grip strength was 78% of the uninvolved wrists. On radiographs, the mean static SL distance was 2.4 mm (2.8 mm before surgery). There was no widening of the SL gap compared to the immediate postoperative gap. The SL angle improved from a mean preoperative value of 61 degrees to 53 degrees immediately after surgery and rose again to 62 degrees at the time of the review. One patient developed a scapholunate advanced collapse wrist stage 2. CONCLUSIONS: Ligament reconstruction using tendon grafts gave satisfactory results to correct reducible chronic SL instability without osteoarthritis. This repair technique achieved a relatively pain-free wrist, with acceptable grip strength and normal SL distance but with a loss in the arc of motion and a loss of correction of SL angle. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic IV

Rupture atypique du tendon flexor digitorum superficialis du majeur chez un grimpeur: analyse biomécanique

International audienceSport climbing is increasingly popular and consultations by climbers in hand surgery departments are on the increase. The pathologies related to this sport concern essentially the pulley system, tendons being rarely affected. We report the case of a male climber who presented an atypical rupture of the flexor superficialis tendon in his left middle finger sustained when using an atypical climbing grip technique: the “hook grip”. This consists in extension of the metacarpophalangeal joints and maximal flexion of the proximal interphalangeal joints with force exerted only on middle phalanx of the middle finger. A biomechanical analysis using finger musculoskeletal modeling was performed to compare the hook grip to other grips, and the patient’s recovery performance was assessed. Adapted functional treatment with physiotherapy seems to have been a good option for the treatment of this atypical lesion since the patient recovered normal use of his finger in daily life. He recovered maximal force in climbing holds. The biomechanical analysis confirmed that the atypical “hook grip” was likely at the origin of the rupture, since flexor digitorum superficialis tendon force for this grip is greater than in other climbing grip techniques. The “hook grip” seems to be dangerous and should be used cautiously by climbers to prevent similar pathology. Additionally, the patient should henceforth be careful when climbing, since the biomechanical model showed that the remaining flexor digitorum profundus tendon was overused.L’escalade est de plus en plus populaire et les consultations des grimpeurs dans les services de chirurgie de la main sont en augmentation. Les pathologies liées à ce sport concernent essentiellement le système des poulies, les tendons étant rarement atteints. Nous décrivons le cas d’un grimpeur masculin qui a présenté une rupture atypique du tendon flexor digitorum superficialis du majeur gauche lors de l’utilisation d’une prise d'escalade sportive atypique - la “prise en crochet”. Cette dernière est caractérisée par une extension des articulations métacarpo-phalangiennes et une flexion maximale des articulations interphalangiennes proximales avec des forces appliquées uniquement sur la phalange moyenne du majeur. Une analyse biomécanique utilisant un modèle musculosquelettique des doigts a été réalisée pour évaluer cette prise par rapport à d’autres, et une évaluation des performances de récupération du patient a été réalisée. Le traitement fonctionnel par kinésithérapie semble être une bonne option pour le traitement de cette lésion atypique en raison de la récupération de la fonction du doigt du patient dans sa vie quotidienne. Le patient a récupéré une force maximale sur les prises. L’analyse biomécanique a confirmé que la prise atypique “en crochet” était certainement à l’origine de cette lésion au vu des forces exercées sur le tendon lors de cette prise en comparaison avec les autres. La “prise en crochet” semble être dangereuse et devrait être utilisée avec prudence par les grimpeurs pour prévenir cette pathologie. De plus, notre patient devra être prudent dans sa pratique de l’escalade en raison de l’hyperutilisation de son flexor digitorum profundus objectivée par le modèle biomécanique