2,491 research outputs found

    Encoding a Qubit into a Cavity Mode in Circuit-QED using Phase Estimation

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    Gottesman, Kitaev and Preskill have formulated a way of encoding a qubit into an oscillator such that the qubit is protected against small shifts (translations) in phase space. The idea underlying this encoding is that error processes of low rate can be expanded into small shift errors. The qubit space is defined as an eigenspace of two mutually commuting displacement operators SpS_p and SqS_q which act as large shifts/translations in phase space. We propose and analyze the approximate creation of these qubit states by coupling the oscillator to a sequence of ancilla qubits. This preparation of the states uses the idea of phase estimation where the phase of the displacement operator, say SpS_p, is approximately determined. We consider several possible forms of phase estimation. We analyze the performance of repeated and adapative phase estimation as the simplest and experimentally most viable schemes given a realistic upper-limit on the number of photons in the oscillator. We propose a detailed physical implementation of this protocol using the dispersive coupling between a transmon ancilla qubit and a cavity mode in circuit-QED. We provide an estimate that in a current experimental set-up one can prepare a good code state from a squeezed vacuum state using 88 rounds of adapative phase estimation, lasting in total about 4μ4 \mu sec., with 94%94\% (heralded) chance of success.Comment: 24 pages, 15 figures. Some minor improvements to text and figures. Some of the numerical data has been replaced by more accurate simulations. The improved simulation shows that the code performs better than originally anticipate

    Evolution of microgastropods (Ellobioidea, Carychiidae): integrating taxonomic, phylogenetic and evolutionary hypotheses

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    BACKGROUND: Current biodiversity patterns are considered largely the result of past climatic and tectonic changes. In an integrative approach, we combine taxonomic and phylogenetic hypotheses to analyze temporal and geographic diversification of epigean (Carychium) and subterranean (Zospeum) evolutionary lineages in Carychiidae (Eupulmonata, Ellobioidea). We explicitly test three hypotheses: 1) morphospecies encompass unrecognized evolutionary lineages, 2) limited dispersal results in a close genetic relationship of geographical proximally distributed taxa and 3) major climatic and tectonic events had an impact on lineage diversification within Carychiidae. RESULTS: Initial morphospecies assignments were investigated by different molecular delimitation approaches (threshold, ABGD, GMYC and SP). Despite a conservative delimitation strategy, carychiid morphospecies comprise a great number of unrecognized evolutionary lineages. We attribute this phenomenon to historic underestimation of morphological stasis and phenotypic variability amongst lineages. The first molecular phylogenetic hypothesis for the Carychiidae (based on COI, 16S and H3) reveals Carychium and Zospeum to be reciprocally monophyletic. Geographical proximally distributed lineages are often closely related. The temporal diversification of Carychiidae is best described by a constant rate model of diversification. The evolution of Carychiidae is characterized by relatively few (long distance) colonization events. We find support for an Asian origin of Carychium. Zospeum may have arrived in Europe before extant members of Carychium. Distantly related Carychium clades inhabit a wide spectrum of the available bioclimatic niche and demonstrate considerable niche overlap. CONCLUSIONS: Carychiid taxonomy is in dire need of revision. An inferred wide distribution and variable phenotype suggest underestimated diversity in Zospeum. Several Carychium morphospecies are results of past taxonomic lumping. By collecting populations at their type locality, molecular investigations are able to link historic morphospecies assignments to their respective evolutionary lineage. We propose that rare founder populations initially colonized a continent or cave system. Subsequent passive dispersal into adjacent areas led to in situ pan-continental or mountain range diversifications. Major environmental changes did not influence carychiid diversification. However, certain molecular delimitation methods indicated a recent decrease in diversification rate. We attribute this decrease to protracted speciation

    Inline self-diffraction dispersion-scan of over octave-spanning pulses in the single-cycle regime

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    We present an implementation of dispersion-scan based on self-diffraction (SD d-scan) and apply it to the measurement of over octave-spanning sub-4-fs pulses. The results are compared with second-harmonic generation (SHG) d-scan. The efficiency of the SD process is derived theoretically and compared with the spectral response retrieved by the d-scan algorithm. The new SD d-scan has a robust inline setup and enables measuring pulses with over-octave spectra, single-cycle durations and wavelength ranges beyond those of SHG crystals, such as the ultraviolet and the deep-ultraviolet.Comment: 8 pages, 5 figure

    Distributed interoperable workflow support for electronic commerce.

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    Abstract. This paper describes a flexible distributed transactional workflow environment based on an extensible object-oriented framework built around class libraries, application programming interfaces, and shared services. The purpose of this environment is to support a range of EC-like business activities including the support of financial transactions and electronic contracts. This environment has as its aim to provide key infrastructure services for mediating and monitoring electronic commerce.

    Hierarchies from D-brane instantons in globally defined Calabi-Yau Orientifolds

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    We construct the first globally consistent semi-realistic Type I string vacua on an elliptically fibered manifold where the zero modes of the Euclidean D1-instanton sector allow for the generation of non-perturbative Majorana masses of an intermediate scale. In another class of global models, a D1-brane instanton can generate a Polonyi-type superpotential breaking supersymmetry at an exponentially suppressed scale.Comment: 4 pages, 4 tables, uses revtex; v2: Discussion of instanton curves improved, typos fixed, references added; v3: version published in PR

    Cascaded Nondegenerate Four-Wave Mixing Technique for High-Power Single-Cycle Pulse Synthesis in the Visible and Ultraviolet Ranges

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    We present a new technique to synthesize high-power single-cycle pulses in the visible and ultraviolet ranges by coherent superposition of a multiband octave-spanning spectrum obtained by highly-nondegenerate cascaded four-wave mixing of femtosecond pulses in bulk isotropic nonresonant media. The generation of coherent spectra spanning over two octaves in bandwidth is experimentally demonstrated using a thin fused silica slide. Full characterization of the intervening multicolored fields using frequency-resolved optical gating, where multiple cascaded orders have been measured simultaneously for the first time, supports the possibility of direct synthesis of near-single-cycle 2.2 fs visible-UV pulses without recurring to complex amplitude or phase control, which should enable many applications in science and technology.Comment: 13 pages, 4 figures. Submitted to Physical Review

    Vioxx: How Strong Is the Case against Merck?

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    The thousands of personal injury cases filed after Merck’s voluntary withdrawal of Vioxx appear difficult to prove. A large obstacle for plaintiffs is the admissibility of epidemiologic studies, which are required to prove specific causation. Pharmaceutical companies spend countless hours and resources developing and researching new drugs. Clinical research began to indicate that there may be an increase in adverse cardiovascular (“CV”) side effects associated with Vioxx. The reliability of this data and how it will work in our courts is a great concern

    Next Stop: Underground. Variable degrees and variety of reasons for cave penetration in terrestrial gastropods

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    Cave-dwelling animals can be classified based on their occurrence in and relationship to the subterranean environment. However, subsurface distribution data and studies addressing the initial causes for animals to enter underground habitats are sparse. By retrieving occurrence data from two voluntary biospeleological land registers in Central Germany, the degree of cave penetration in terrestrial gastropods was investigated, thus to infer potential evolutionary drivers. In total, 66 identified gastropod species entered the subterranean environment with 23 of the species also recorded from the dark zone. Gastropods possessed variable degrees of cave penetration and no obligate cave forms were observed. A decline of occurrence records from the entrance to the dark zone was the most prominent pattern. Nevertheless, several species were collected from all three light zones (i.e. entrance, transition and dark). A variety of potential reasons can be inferred to explain their subsurface appearance: exploitation of alternative food sources, aphotic above-ground movement, mating sites, temporal, seasonal and long-term refugia, and chance. Moreover, the results imply a frequent migration of species between the interconnected light zones and the surface. Consequently, terrestrial gastropods should be considered when investigating the origin and importation of allochthonous resources in caves
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