High-Fidelity Teleportation of Independent Qubits

Quantum teleportation is one of the essential primitives of quantum communication. We suggest that any quantum teleportation scheme can be characterized by its efficiency, i.e. how often it succeeds to teleport, its fidelity, i.e. how well the input state is reproduced at the output, and by its insensitivity to cross talk, i.e. how well it rejects an input state that is not intended to teleport. We discuss these criteria for the two teleportation experiments of independent qubits which have been performed thus far. In the first experiment (Nature {\bf 390},575 (1997)) where the qubit states were various different polarization states of photons, the fidelity of teleportation was as high as 0.80 $\pm$ 0.05 thus clearly surpassing the limit of 2/3 which can, in principle, be obtained by a direct measurement on the qubit and classical communication. This high fidelity is confirmed in our second experiment (Phys. Rev. Lett. {\bf 80}, 3891 (1998)), demonstrating entanglement swapping, that is, realizing the teleportation of a qubit which itself is still entangled to another one. This experiment is the only one up to date that demonstrates the teleportation of a genuine unknown quantum state.Comment: 13 pages, Latex, 5 figures(eps), to appear in Journal of Modern Optic

A Mach-Zehnder Interferometer for a Two-Photon Wave Packet

We propose an experiment that permits observation of the de Broglie two-photon wave packet behavior for a pair of photons, using a Mach-Zehnder interferometer. It is based on the use of pulsed lasers to generate pairs of photons via spontaneous parametric down-conversion and the post-selection of events. It differs from previous realizations by the use of a third time-correlated photon to engineer the state of the photons. The same technique can give us which-path information via an ``interaction-free'' experiment and can be used in other experiments on the foundations of quantum mechanics related to wave-particle duality and to nonlocality.Comment: Submmited for publication in Physical Review

Advances and challenges in predicting the impact of lymphatic filariasis elimination programmes by mathematical modelling

Mathematical simulation models for transmission and control of lymphatic filariasis are useful tools for studying the prospects of lymphatic filariasis elimination. Two simulation models are currently being used. The first, EPIFIL, is a population-based, deterministic model that simulates average trends in infection intensity over time. The second, LYMFASIM, is an individual-based, stochastic model that simulates acquisition and loss of infection for each individual in the simulated population, taking account of individual characteristics. For settings like Pondicherry (India), where Wuchereria bancrofti infection is transmitted by Culex quinquefasciatus, the models give similar predictions of the coverage and number of treatment rounds required to bring microfilaraemia prevalence below a level of 0.5%. Nevertheless, published estimates of the duration of mass treatment required for elimination differed, due to the use of different indicators for elimination (EPIFIL: microfilaraemia prevalence < 0.5% after the last treatment; LYMFASIM: reduction of microfilaraemia prevalence to zero, within 40 years after the start of mass treatment). The two main challenges for future modelling work are: 1) quantification and validation of the models for other regions, for investigation of elimination prospects in situations with other vector-parasite combinations and endemicity levels than in Pondicherry; 2) application of the models to address a range of programmatic issues related to the monitoring and evaluation of ongoing control programmes. The models' usefulness could be enhanced by several extensions; inclusion of different diagnostic tests and natural history of disease in the models is of particular relevance

Synthesis of breathy vowels: some research methods.

Abstract. When vowels are synthesised by means of a source-filter model, a delta-pulse train is often used as a source signal. Although breathiness can to some extent be simulated by using a sophisticated glottal-source model, a more natural simulation of breathiness requires the addition of aspiration noise. When stationary noise is used, however, the noise is to a large extent perceived as coming from a separate sound source which hardly contributes to the breathy timbre of the vowel. This problem can be solved by using noise with a temporal envelope of the same periodicity as the pulse train. In a simple source-filter model, a combination of lowpass-filtered pulses and synchronous highpass-filtered noise bursts of equal energy was used as a source signal. In this way, the noise was no longer perceived as a separate sound, but integrated perceptually with the strictly periodic part of the signal. It will be shown that this integration consists of both a reduction of the loudness of the separate noise stream and a timbre change in the breathy vowel. Zusammenfassung. Bei der Synthese von Vokalen mit einem Quellen-Filtermodell wird als Quellensigna[ oft eine Deltapulsfolge verwendet. Obwohl eine hauchige Stimme bis zu einem gewissen Grad mit einem verfeinerten Glottal-Quellenmodell simuliert werden kann, erfordert eine natiirlich klingende Simulation doch die Addition yon Rauschen. Wenn zu diesem Zweck allerdings station~ires Rauschen verwendet wird, wird dieses meist als yon einer getrennten Signalquelle stammend wahrgenommen und tr~gt damit kaum zum Eindruck eines gehauchten Vokals bei. Dieses Problem kann dadurch gelOst werden, dab das Rauschen mit einer zeitlichen Einhiillenden versehen wird, deren Periodizit~it dieselbe ist wie die der Pulsfolge. In einem einfachen Quellen-Filtermodell wurde eine Kombination yon tiefpaBgefilterten Pulsen und synchronen hochpal~gefilterten Rauschpulsen mit dergleichen Energie als Quellensignal verwendet. Dadurch wurde das Rauschen nicht mehr als getrenntes Signal wahrgenommen, sondern perzeptiv mit dem periodischen Signalanteil integriert. In dem Beitrag wird gezeigt, dab diese Verschmelzung einerseits auf einer Verringerung der Lautheit des Rauschsignals und andererseits auf einer Klangfarben~inderung im gehauchten Vokal beruht. R6sum6. La synth6se de voyelles au moyen d&apos;un mod61e source-filtre s&apos;effectue souvent avec un train d&apos;impulsions delta comme signal d&apos;entr6e. Bien que des modules sophistiqu6s de la source glottale puissent ~tre employ6s, dans une certaine mesure, afin de simuler une voix souffi6e, une simulation plus naturelle exige l&apos;addition d&apos;un bruit d&apos;aspiration. Cependant, lorsqu&apos;un bruit stationnaire est employ6, il sera per~u en bonne partie comme provenant d&apos;une source sonore s6par6e qui ne contribue pas au timbre souffi6 de la voyelle. Ce probl6me peut 6tre r6solu en utilisant un bruit ayant une enveloppe temporelle de la m6me p6riodicit6 que le train d&apos;impulsions. Dans un simple mod61e source-filtre, des impulsions filtr6es passe-bas combin6es ~ un bruit pulsatif synchrone filtr6 passe-haut ~ 6nergie 6galis6e ont 6t6 employ6es comme signal de source. De cette fa~on, le bruit n&apos;est plus per~u s6par6ment, mais est int6gr6 perceptuellement ~t la partie strietement p6riodique du signal. II sera d6montr6 que cette int6gration consiste ~ la lois en une r6duction de la force sonore du bruit et en une alt6ration du timbre de la voyelle souffi6e

Experimental violation of a spin-1 Bell inequality using maximally-entangled four-photon states

We demonstrate the first experimental violation of a spin-1 Bell inequality. The spin-1 inequality is a calculation based on the Clauser, Horne, Shimony and Holt formalism. For entangled spin-1 particles the maximum quantum mechanical prediction is 2.552 as opposed to a maximum of 2, predicted using local hidden variables. We obtained an experimental value of 2.27 $\pm 0.02$ using the four-photon state generated by pulsed, type-II, stimulated parametric down-conversion. This is a violation of the spin-1 Bell inequality by more than 13 standard deviations.Comment: 5 pages, 3 figures, Revtex4. Problem with figures resolve

Modulation of calcium oxalate monohydrate crystallization kinetics in vitro

Modulation of calcium oxalate monohydrate crystallization kinetics in vitro. The effects of several low and high molecular weight (mol wt) compounds on the kinetics of calcium oxalate crystallization were examined using a seeded crystal growth method in which the solubility, the growth and the agglomeration of calcium oxalate crystals were measured as three separate and system-independent parameters. Git-rate, magnesium, phosphate, pyrophosphate, chondroitinsulphate, pen-tosanpolysulphate and heparin were tested in a wide range of concentrations. The solubility of calcium oxalate crystals Was increased only by citrate and magnesium. The crystal growth was inhibited by all compounds tested, but those with the high mol wt had the greatest effect at low concentrations. In contrast, inhibition of crystal agglomeration was achieved only by the low mol wt compounds; citrate was found to be the most potent inhibitor at concentrations likely to be present in normal urine. The high mol wt substances, despite their potent crystal growth inhibitory activity, had no effect on agglomeration. The results show that growth and agglomeration of calcium oxalate crystals are separate processes which are differently modulated by various compounds. They further provide a possible explanation for the pathogenetic role of citrate in hypocitraturic renal stone disease

The Long Term Effect of Current and New Interventions on the New Case Detection of Leprosy: A Modeling Study

Leprosy is a contagious disease that will remain prevalent, despite the declining number of patients worldwide over the last century. With approximately 250,000 new cases detected annually, leprosy is far from being eradicated. Leprosy can be treated with drugs after disease detection

Meaning interventions in schools: Strategies for supporting healthy development and wellbeing in the lives of youth

Human beings inherently make meaning of the world, interpreting themselves in context and utilizing these representations to determine what to think, how to feel, and in what way to act. Developing meaning in life appears to be a highly nuanced, personal journey and yet, research suggests that those who experience their lives as meaningful enjoy multiple physical and psychological benefits and are protected from various health risks. Beyond establishing a firm sense that life is meaningful, studies suggest that people of all ages who can ‘make meaning’ of their experiences, especially difficult experiences, may be protected from developing some mental and physical health concerns. Childhood and adolescence may be pivotal periods for the development of this well-being resource, and school offers an especially promising context for fostering meaning. Yet, there have been few articles that have explored how meaning and meaning-making can be woven into the school day. The current article attempts to address this gap in the literature by defining meaning and meaning-making, discussing the relevance of meaning from a developmental framework, and offering suggestions for applications for teachers and providers during the school day