1,720,964 research outputs found
With great power comes great fidelity
No full textMany quantum applications require the careful preparation of quantum harmonic oscillators. The combination of a high-power microwave drive and weak nonlinearity enables fast control of such systems, with implications for quantum computing and metrologyGreen Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Andersen La
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Characterization of superconducting parametric amplifiers
No full textSuperconducting parametric amplifiers have been developed for fast and highfidelity single shot readout of superconducting qubits. The nonliniarity re-quired for those amplifiers is either based on various types of Josephsonjunctions or high kinetic inductance materials. The Andersen Lab currentlydevelops a novel type of superconducting parametric amplifiers based onsuperconducting-semiconducting hybrid nanowires, which will allow for in-situ tuning of the amplifier characteristics with a gate voltage.To prepare for the required performance tests of nanowire-based para-metric amplifiers, we characterize a commercially available travelling waveparametric amplifier in terms of 5 figures of merit: gain, bandwidth, satu-ration power, noise temperature and quantum efficiency. We find a state ofthe art amplifier performances, but also detect several hardware problemsin the measurement setup, which must be solved prior to further test. Themethod implemented here can be generalized to the characterization of alltypes superconducting parametric amplifiers.Applied Science
Nanowire Josephson junctions in superconducting circuits
No full textThe Josephson effect is a quintessential topic of condensed matter physics. It has stimulated decades of fundamental research, leading to a plethora of applications from metrology to outer space. In addition, it is set to play a crucial role in the development of quantum computers, forming the dissipationless non-linear inductance that lies at the core of superconducting qubits. While they are traditionally realized using oxide based tunnel barriers, in this thesis we construct Josephson junctions from non-insulating materials such as semiconducting nanowires and quantum dots. We investigate how their highly nontrivial interplay with superconductivity can lead to new effects, both of fundamental interest and of relevance for quantum applications. To study these effects we make use the exhaustive toolbox available for superconducting circuits, allowing us to probe the junction behavior to beyond what is possible with conventional transport techniques.The first experimental chapter of this thesis examines the behaviour of a transmon that hosts a highly transparent semiconducting weak-link as the Josephson junction. In this system we find spectroscopic evidence for the predicted vanishing of Coulomb effects in open superconducting islands, in accordance with theoretical predictions from 1999.In the second experiment we deterministically place a quantum dot inside the junction of a transmon circuit. We then demonstrate that by using microwave spectroscopy we are able to accurately probe the energy-phase relationship of the Josephson junction over a vast regime of parameter space. This reveals the remnants of a quantum phase transition, and allows us to probe the time dynamics of the junction parity.We subsequently use the same type of device to reveal the predicted spin-splitting of the Andreev bound states in a quantum dot with superconducting leads, as brought about by the spin-orbit interaction. When combined with a magnetic field, this is shown to result in the anomalous Josephson effect. Furthermore, we demonstrate that transitions between the spin-split quantum dot states can be directly driven with microwaves.This motivated the investigation of a novel superconducting spin qubit, performed in the fourth experiment. Here we demonstrate rapid, all-electric qubit manipulation in addition to detailed coherence characterization. We ultimately show signatures of strong coherent coupling between the superconducting spin qubit and the transmon into which it is embedded, setting the stage for future research of this nascent qubit platform.In the fifth and final experiment, we utilize a different approach compared to the preceding chapters. While we once-more construct transmons based on semiconducting weak-links, we now do so to leverage the intrinsic magnetic field resilience of semiconducting nanowires. This allows us to use a single device to study the mitigation of phonon-induced quasiparticle losses by trapping the phonons using both super and normal-state conductors. This thesis concludes by discussing several ideas and proposals that aim to leverage the alternative Josephson junctions studied in this thesis. Combined with the results of the preceding chapters, this shows that hybrid superconducting circuits can be used to obtain deep insights into the fundamental physics governing their constituent junctions, and opens avenues towards building better qubits.QRD/Kouwenhoven La
Magnetic field resilient lumped element superconducting resonators
No full textResonators are useful structures due to their simplicity in modeling, design, fabrication and measurement. They can be measured over a wide range of frequencies, power and temperatures, making them convenient for many experiments. Recently, superconducting resonators started being used to investigate microscopic phenomena which require applied magnetic fields of the order of 1T, such as Majorana physics. For this kind of applications it is important that resonators maintain high quality factors in the presence of magnetic fields. A suitable candidate easy to fabricate, resilient to applied fields, and simple capacitive coupling is the lumped element resonator. Such a type of resonator has already been used for some experiments that require magnetic fields, but a systematic study on the resonator’s optimal geometry is yet to be undertaken. The aim of this thesis is to investigate the role of lumped element resonator geometry in its quality factor. That is how to optimize the resonator’s design for enhanced performance of the resonator even in the presence of applied magnetic fields.Applied Science
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