Arbitrary state controlled-unitary gate by adiabatic passage

We propose a robust scheme involving atoms fixed in an optical cavity to directly implement the universal controlled-unitary gate. The present technique based on adiabatic passage uses novel dark states well suited for the controlled-rotation operation. We show that these dark states allow the robust implementation of a gate that is a generalisation of the controlled-unitary gate to the case where the control qubit can be selected to be an arbitrary state. This gate has potential applications to the rapid implementation of quantum algorithms such as of the projective measurement algorithm. This process is decoherence-free since excited atomic states and cavity modes are not populated during the dynamics.Comment: 6 pages, 6 figure, submitted to Phys. Rev.

CNOT gate by adiabatic passage with an optical cavity

We propose a scheme for the construction of a CNOT gate by adiabatic passage in an optical cavity. In opposition to a previously proposed method, the technique is not based on fractional adiabatic passage, which requires the control of the ratio of two pulse amplitudes. Moreover, the technique constitutes a decoherence-free method in the sense that spontaneous emission and cavity damping are avoided since the dynamics follows dark states.Comment: 6 pages, 4 figures, submitted to EPJ

Exploring User-Provided Connectivity

Network services often exhibit positive and negative externalities that affect users\u27 adoption decisions. One such service is user-provided connectivity or UPC. The service offers an alternative to traditional infrastructure-based communication services by allowing users to share their home base connectivity with other users, thereby increasing their access to connectivity. More users mean more connectivity alternatives, i.e., a positive externality, but also greater odds of having to share one\u27s own connectivity, i.e., a negative externality. The tug of war between positive and negative externalities together with the fact that they often depend not just on how many but also which users adopt, make it difficult to predict the service\u27s eventual success. Exploring this issue is the focus of this paper, which investigates not only when and why such services may be viable, but also explores how pricing can be used to effectively and practically realize them

Optical parametric oscillation with distributed feedback in cold atoms

There is currently a strong interest in mirrorless lasing systems, in which the electromagnetic feedback is provided either by disorder (multiple scattering in the gain medium) or by order (multiple Bragg reflection). These mechanisms correspond, respectively, to random lasers and photonic crystal lasers. The crossover regime between order and disorder, or correlated disorder, has also been investigated with some success. Here, we report one-dimensional photonic-crystal lasing (that is, distributed feedback lasing) with a cold atom cloud that simultaneously provides both gain and feedback. The atoms are trapped in a one-dimensional lattice, producing a density modulation that creates a strong Bragg reflection with a small angle of incidence. Pumping the atoms with auxiliary beams induces four-wave mixing, which provides parametric gain. The combination of both ingredients generates a mirrorless parametric oscillation with a conical output emission, the apex angle of which is tunable with the lattice periodicity

Field evaluation of two rapid diagnostic tests for Neisseria meningitidis serogroup A during the 2006 outbreak in Niger.

The Pastorex((R)) (BioRad) rapid agglutination test is one of the main rapid diagnostic tests (RDTs) for meningococcal disease currently in use in the "meningitis belt". Earlier evaluations, performed after heating and centrifugation of cerebrospinal fluid (CSF) samples, under good laboratory conditions, showed high sensitivity and specificity. However, during an epidemic, the test may be used without prior sample preparation. Recently a new, easy-to-use dipstick RDT for meningococcal disease detection on CSF was developed by the Centre de Recherche Médicale et Sanitaire in Niger and the Pasteur Institute in France. We estimate diagnostic accuracy in the field during the 2006 outbreak of Neisseria meningitidis serogroup A in Maradi, Niger, for the dipstick RDT and Pastorex((R)) on unprepared CSF, (a) by comparing each test's sensitivity and specificity with previously reported values; and (b) by comparing results for each test on paired samples, using McNemar's test. We also (c) estimate diagnostic accuracy of the dipstick RDT on diluted whole blood. We tested unprepared CSF and diluted whole blood from 126 patients with suspected meningococcal disease presenting at four health posts. (a) Pastorex((R)) sensitivity (69%; 95%CI 57-79) was significantly lower than found previously for prepared CSF samples [87% (81-91); or 88% (85-91)], as was specificity [81% (95%CI 68-91) vs 93% (90-95); or 93% (87-96)]. Sensitivity of the dipstick RDT [89% (95%CI 80-95)] was similar to previously reported values for ideal laboratory conditions [89% (84-93) and 94% (90-96)]. Specificity, at 62% (95%CI 48-75), was significantly lower than found previously [94% (92-96) and 97% (94-99)]. (b) McNemar's test for the dipstick RDT vs Pastorex((R)) was statistically significant (p<0.001). (c) The dipstick RDT did not perform satisfactorily on diluted whole blood (sensitivity 73%; specificity 57%).Sensitivity and specificity of Pastorex((R)) without prior CSF preparation were poorer than previously reported results from prepared samples; therefore we caution against using this test during an epidemic if sample preparation is not possible. For the dipstick RDT, sensitivity was similar to, while specificity was not as high as previously reported during a more stable context. Further studies are needed to evaluate its field performance, especially for different populations and other serogroups

Z-11-TETRADECENYL ACETATE: SEX ATTRACTANT OF AGAPETA ZOEGANA (LEPIDOPTERA: TORTRICIDAE), A POTENTIAL SPECIES FOR THE BIOLOGICAL CONTROL OF KNAPWEED

In Canada, 78 of the most important weed species are introductions from Eurasia (Frankton and Mulligan 1970). Classical biological control aims to reduce the density of alien weeds below the economic threshold through introduction of specific herbivores from the native distribution area (Peschken 1979). During extended field surveys in central and southeastern Europe, the Commonwealth Institute of Biological Control established the root-mining tortricid Agapeta zoegana Haw. as a promising control agent for Centaurea diffusa Lam. and C. maculosa Lam., 2 important ranch weeds in southwestern Canada (Harris and Myers 1984) and the northwestern United States (Maddox 1982). Due to the limited host range and suitable climatic conditions this moth was chosen for introduction into North America (Müller et al. 1982; Müller 1984). We wish to report an attractant that may be used to monitor the establishment of this beneficial species in its new habita

How will livestock systems in cotton savannahs adapt to increased land pressure and forage use for biofuels production?

L'intégration de l'élevage dans les espaces agricoles soudaniens s'est beaucoup accentuée durant les 50 dernières années. L'accroissement démographique humain et animal, ainsi que le changement climatique, entraînent de fortes pressions sur le foncier et sur les ressources végétales qui laissent peu de place pour de nouvelles activités agricoles, dont celles à finalité énergétique, sans une révision globale de l'utilisation des terroirs et des systèmes de production. Les exemples de territoires villageois dans la zone cotonnière illustrent cette situation en démontrant les limites des usages des biomasses des différents espaces. De nombreuses techniques agricoles, agroforestières et zootechniques pour l'aménagement des terroirs, l’intensification écologique des systèmes fourragers et de la gestion des troupeaux sont connues ; elles ont souvent été expérimentées mais de façon déconnectée des réalités sociales et économiques de la gestion de l'espace, de la rémunération du travail, et des systèmes de production en général. Leur relecture pour les conjuguer avec l'introduction éventuelle de cultures à des fins énergétiques, doit prendre en compte prioritairement trois dimensions : (i) les dynamiques foncières qu'il faut infléchir vers la sécurisation pour tous, (ii) la définition, l'évaluation et la rémunération de services environnementaux et (iii) l'accroissement de la productivité animale intégrée dans des filières et des marchés sécurisés et rémunérateurs. Les auteurs s'efforcent d'analyser ces évolutions et de formuler des recommandations pour une vision globale du développement rural considérant l'ensemble des enjeux notamment celui d'un élevage durable dans des contextes en changements

A new regime of anomalous penetration of relativistically strong laser radiation into an overdense plasma

It is shown that penetration of relativistically intense laser light into an overdense plasma, accessible by self-induced transparency, occurs over a finite length only. The penetration length depends crucially on the overdense plasma parameter and increases with increasing incident intensity after exceeding the threshold for self-induced transparency. Exact analytical solutions describing the plasma-field distributions are presented.Comment: 6 pages, 2 figures in 2 separate eps files; submitted to JETP Letter