241 research outputs found
Experimental techniques for continuous variable photonic quantum information
No full textQuantum optics is central to emerging quantum technologies such as quantum metrology and quantum information. The continuous variable (CV) approach to encoding information in a physical system, for example the electromagnetic field quadratures has significant advantages over discrete variables (DV) encoding. CV offers higher density encoding in a single optical state and on-demand state preparation for example. However, techniques for CV preparation, manipulation and measurement are not as well developed as the corresponding DV approach. In this thesis we present methods to characterize quantum detectors that operate in the CV regime, and discuss their application to CV state preparation. A quantum detector is described by its positive operator valued measure (POVM) set, with one operator for each measurement outcome. We present an experimental scheme for detector tomography, that is reconstruction of the POVM set of an unknown detector by means of measurement outcomes for a set of tomographically complete input states. We use this scheme to experimentally determine the POVM set of an avalanche photodiode (APD) and a time-multiplexed-detector (TMD) and compare the results to models of the detectors. We introduce a weak-homodyne photon-number-resolving detector (PNRD) , which uses a weak local oscillator beam to set a phase reference for the detection process. We develop a theoretical description of the sensitivity regimes for this detector using the Wigner phase space picture. We also present experimental detector tomography for a weak-homodyne detector based on two APDs. In many cases it is sufficient to calibrate the efficiencies of previously characterized PNRDs. We experimentally demonstrate a scheme using correlated photons produced by spontaneous parametric downconversion (SPDC) to determine the efficiencies of PNRDs, based on the photon number statistics of the source. The same SPDC source is also used to demonstrate preparation of photonic states in the photon number basis and for a first proof-of-principle experiment with a weak-homodyne PNRD based on a TMD.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Quantum detector tomography of a time-multiplexed superconducting nanowire single-photon detector at telecom wavelengths
No full textSuperconducting nanowire single-photon detectors (SNSPDs) are widely used in telecom wavelength optical quantum information science applications. Quantum detector tomography allows the positive-operator-valued measure (POVM) of a single-photon detector to be determined. We use an all-fiber telecom wavelength detector tomography test bed to measure detector characteristics with respect to photon flux and polarization, and hence determine the POVM. We study the SNSPD both as a binary detector and in an 8-bin, fiber based, Time-Multiplexed (TM) configuration at repetition rates up to 4 MHz. The corresponding POVMs provide an accurate picture of the photon number resolving capability of the TM-SNSPD
Music for classical guitar by South African composers : a historical survey, notes on selected works and a general catalogue
No full textIncludes abstract.Includes bibliographical references (leaves 296-309).This is the first comprehensive investigation of music for, or including, the classical guitar by South African composers. The focus of this research has been, firstly, to uncover as much of the repertoire as possible, and, secondly, to collate, study, catalogue and report on the information. A brief historical survey of the guitar in South Africa provides the context within which this study was conducted. The primary sources of quantitative data collection were through the archival catalogues of the South African Music Rights Organisation and through personal contact with guitarists, composers and guitar teachers. Other sources consulted were publishers, broadcasting corporations, recording companies, libraries and the internet. The body of the dissertation comprises biographical sketches, background notes, analyses and technical notes on 17 selected solo and chamber works dating from 1947 to 2007 by some of South Africa's most prominent composers and guitaristcomposers. The repertoire ranges in style from the traditional and ethnically inspired to the experimental and abstract. As this is an empirical survey, each selected entry includes details on instrumentation, duration, level of difficulty, number of pages, scordatura, commissions or requests, sources or publishers, premières and recordings. A biography of each composer is provided as well as background notes which offer an overview of the selected work. The notes discuss historical, cultural, musical and extra-musical influences, and frequently include references to interview material. The commentaries on the selected works, with musical examples, include an analytical component describing structure, form, stylistic and compositional elements, while the technical observations include performance suggestions and a grading for each work
An annotated catalogue of selected works for clarinet by South African composers
No full textThe dissertation consists of an annotated catalogue of nineteen selected works for clarinet by South African composers. These are presented in chronological order, based on the year of composition. A short biographyof the composer is given before the work is discussed. Of the analysed works, all those for solo clarinet or for clarinet and piano have been graded. A thesis of a similar nature, written in 1989 by L.A. Hartshorne, entitled ""The Compositions for Clarinet by South African Composers"", contains details of twenty-four works written between 1928 and circa 1981. The majority of the compositions analysed in the current dissertation were written from around 1981 onwards, and to some extent, therefore, this research could be seen as complementary to the information contained in the aforementioned thesis. An addendum lists all the South African works featuring solo clarinet that the author was able to trace. These include solo works, cham ber works for up to nineteen instruments and concerto-type works with strings or orchestra
The Christian Message in a Postmodern World: a critical re-appropriation of Hendrik Kraemer's theology of religions
No full textThis thesis is a critical re-appropriation of Hendrik Kraemer's theology of religions. Part I introduces theology of religions through the now familiar threefold typology: Kari Earth represents 'exclusivism,' Kari Rahner, 'inclusivism,' and John Hick, 'pluralism' (Chapter 1). It then argues that the typology implicitly represents non-pluralist approaches as theologically deficient and ethically insensitive while masking problems in pluralist positions (Chapter 2). It thus releases Kraemer from the typology and from the more emotive charges directed against 'exclusivism.' Part II chronologically and thematically surveys Kraemer's theology of religions, describing his missiological and theological contexts (Chapter 3) and summarising his major works (Chapter 4). The crux of the argument comes in Part III. First, a survey of the contemporary philosophical climate is offered through a summary and critique of Jean-Frangois Lyotard's interpretation of the postmodern condition Subsequently, three theological responses are assessed with Mark C. Taylor's a/theology and John Milbank's theology presented as avoidable extremes while the work of Hans Frei and George Lindbeck is offered as a mediating position which is dubbed 'postmodern orthodoxy' (Chapter 5). Second, after reviewing key themes in Kraemer's position, theological and phenomenological criticisms are outlined and evaluated. Though they do not seriously threaten the position, these criticisms prohibit extreme interpretations of, and lead to slight modifications in, Kraemer's work (Chapter 6). Finally, when re-read through the lenses of postmodern orthodoxy, Kraemer's thought is shown to offer to contemporary theology of religions avenues of theological creativity which are nevertheless faithful to the Christian tradition (Chapter 7). The thesis concludes that Hendrik Kraemer's theology of religions is worthy of critical re- appropriation
The distribution of the number of points modulo an integer on elliptic curves over finite fields
No full textLet Fq be a finite field and let b and N be integers. We prove explicit estimates for the probability that the number of rational points on a randomly chosen elliptic curve E over Fq equals b modulo N . The underlying tool is an equidistribution result on the action of Frobenius on
the N-torsion subgroup of E. Our results subsume and extend previous work by Achter and Gekeler.sponsorship: The authors are very grateful to the anonymous referee of a prior submission of this document, to the anonymous referee of the current submission, to Hendrik W. Lenstra for suggesting the use of Chebotarev's density theorem, and to Barry Mazur and Bjorn Poonen for their helpful comments on modular curves. Both authors thank F.W.O.-Vlaanderen for its financial support. The first author thanks the Massachusetts Institute of Technology for its hospitality. (F.W.O.-Vlaanderen)status: Publishe
The Quest for Citations: Drivers of Article Impact
No full textWhy do some articles become building blocks for future scholars, while many others remain unnoticed? We aim to answer this question by contrasting, synthesizing and simultaneously testing three scientometric perspectives – universalism, social constructivism and presentation – on the influence of article and author characteristics on article citations. To do so, we study all articles published in a sample of five major journals in marketing from 1990 to 2002 that are central to the discipline. We count the number of citations each of these articles has received and regress this count on an extensive set of characteristics of the article (i.e. article quality, article domain, title length, the use of attention grabbers and expositional clarity), and the author (i.e. author visibility and author personal promotion). We find that the number of citations an article in the marketing discipline receives, depends upon “what one says†(quality and domain), on “who says it†(author visibility and personal promotion) and not so much on “how one says it†(title length, the use of attention grabbers, and expositional clarity). Our insights contribute to the marketing literature and are relevant to scientific stakeholders, such as the management of scientific journals and individual academic scholars, as they strive to maximize citations. They are also relevant to marketing practitioners. They inform practitioners on characteristics of the academic journals in marketing and their relevance to decisions they face. On the other hand, they also raise challenges towards making our journals accessible and relevant to marketing practitioners: (1) authors visible to academics are not necessarily visible to practitioners; (2) the readability of an article may hurt academic credibility and impact, while it may be instrumental in influencing practitioners; (3) it remains questionable whether articles that academics assess to be of high quality are also managerially relevant.Impact;Citation Analysis;Referencing;Scientometrics;Cite
Bridging Particle and Wave Sensitivity in a Configurable Detector of Positive Operator-Valued Measures
No full textPeer reviewed: YesNRC publication: Ye
Glacial-to-deglaical changes in South Pacific surface water oceanography - centennial-scale age control -
No full textGlacial-to-interglacial changes in atmospheric pCO2 are considered as largely controlled by processes in the Southern Ocean. In particular, upwelling both near coastlines and along the Polar Front is regarded as a major pathway of old CO2 from the deep ocean up to the sea surface and atmosphere, hence plays an important role in regulating the CO2 exchange between ocean and atmosphere. At the beginning of the last glacial termination, changes in ocean overturning circulation in the Southern Ocean probably triggered two huge events of CO2 outgassing from a deep-ocean reservoir into the atmosphere as revealed by Antarctic ice core records 1. They parallel two intervals of rapidly decreasing atmospheric 13C 2 and ∆14C 3. They probably concurred with two intervals of enhanced ocean upwelling, directly linking increased ventilation of the deep ocean to the deglacial rise in atmospheric CO2. To constrain the precise timing and origin of released CO2 we used paired records of marine 14C reservoir ages from the Pacific sector of the Southern Ocean, established by means of the 14C Plateau Tuning method 4. High surface ocean reservoir ages serve as tracer for upwelled old water masses. They were obtained from our centennial-scale resolution planktonic radiocarbon records of sediment cores off southern New Zealand and southern Chile. During the last peak glacial our 14C ages reveal planktonic reservoir ages of 1600 - 2200 yr exceeding previous estimates 5,6 by 400-1200 yr, but well agree to the previously reported high value of 1970 yr 7. Right at the onset of the last deglacial our records suggest an extreme drop down to a very low reservoir age of 200-400 yr matching the low estimates of 300-400 yr by 5,6,7,8. During terminal Heinrich-1 times, the values once more reached 1100 yr. This pattern of increased reservoir ages during peak glacial times (and the B/A) and strongly reduced values during the early deglacial parallels and precedes the 13C trends of atmospheric CO2 each and may have great implications for both constraining the history of past deep-water ages and related changes in the CO2 (1‰ 14C -1.22 μmol DIC kg−1) 4 storage of South Pacific deep waters.
(1) Marcott et al. 2014, Nature Vol. 514, 616
(2) Schmitt et al. 2013, Science Vol. 336, 711
(3) Bronk Ramsey et al. 2012, Science Vol. 338, 370
(4) Sarnthein et al. 2013, Clim. Past Vol. 9, 2595
(5) Pahnke et al. 2005, Science Vol. 307, 1741
(6) Ronge et al. 2016, Nature Comm. Vol. 7, 11487
(7) Sikes et al. 2000, Nature Vol. 405, 555
(8) Siani et al. 2013, Nature Comm. Vol. 4. 275
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