1,720,958 research outputs found
A two-module trapped-ion quantum computer prototype
No full textQuantum information technology has the potential to revolutionise a wide range of research fields and to have a profound impact on society. Today, work towards a universal quantum computer is benefiting from recent breakthroughs in quantum hardware engineering. One of the most promising approaches is based on quantum computing modules that are networked via ion shuttling. The modules make use of microfabricated electrodes that create electric fields to confine ensembles of ion qubits. Combining this modular approach with strong magnetic field gradients and long-wavelength radiation quantum gate technology can significantly improve system scalability. Nevertheless, the realisation and simultaneous integration of all the core characteristics of such modules remains an intrinsically challenging task. This doctoral thesis investigates novel techniques and components critical to the engineering of this architecture. A prototype ion trapping system is constructed for the operation of two microfabricated ion-trap modules, which will enable the execution of key operations for networked quantum logic, i.e. high-fidelity one- and two-qubit gates, and shuttling of ion qubits between both modules to realise a matter-based quantum link. In this scheme, high-fidelity quantum gates require a large magnetic field gradient to be generated at the ion position. To achieve this, novel current-carrying wire structures directly embedded within the ion-trap module were developed. These offer a scalable solution to this challenge. The operation of ion traps at cryogenic temperatures is also desirable to further enhance quantum gate fidelities. A thermal model of the ion trap is presented and a cryogenic cooling system capable of meeting the requirements of a large-scale ion-trap architecture is demonstrated. Finally, the constructed two-module ion-trap apparatus is presented. This provides a viable set-up for the execution of these key operations, paving the way towards the realisation of a universal quantum computer
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A two-module trapped-ion quantum computer prototype
No full textQuantum information technology has the potential to revolutionise a wide range of research fields and to have a profound impact on society. Today, work towards a universal quantum computer is benefiting from recent breakthroughs in quantum hardware engineering. One of the most promising approaches is based on quantum computing modules that are networked via ion shuttling. The modules make use of microfabricated electrodes that create electric fields to confine ensembles of ion qubits. Combining this modular approach with strong magnetic field gradients and long-wavelength radiation quantum gate technology can significantly improve system scalability. Nevertheless, the realisation and simultaneous integration of all the core characteristics of such modules remains an intrinsically challenging task. This doctoral thesis investigates novel techniques and components critical to the engineering of this architecture. A prototype ion trapping system is constructed for the operation of two microfabricated ion-trap modules, which will enable the execution of key operations for networked quantum logic, i.e. high-fidelity one- and two-qubit gates, and shuttling of ion qubits between both modules to realise a matter-based quantum link. In this scheme, high-fidelity quantum gates require a large magnetic field gradient to be generated at the ion position. To achieve this, novel current-carrying wire structures directly embedded within the ion-trap module were developed. These offer a scalable solution to this challenge. The operation of ion traps at cryogenic temperatures is also desirable to further enhance quantum gate fidelities. A thermal model of the ion trap is presented and a cryogenic cooling system capable of meeting the requirements of a large-scale ion-trap architecture is demonstrated. Finally, the constructed two-module ion-trap apparatus is presented. This provides a viable set-up for the execution of these key operations, paving the way towards the realisation of a universal quantum computer
Fabrication of surface ion traps with integrated current carrying wires enabling high magnetic field gradients
No full textA major challenge for quantum computers is the scalable simultaneous execution of quantum gates. One approach to address this in trapped ion quantum computers is the implementation of quantum gates based on static magnetic field gradients and global microwave fields. In this paper, we present the fabrication of surface ion traps with integrated copper current carrying wires embedded inside the substrate below the ion trap electrodes, capable of generating high magnetic field gradients. The copper layer's measured sheet resistance of 1.12 mO/sq at room temperature is sufficiently low to incorporate complex designs, without excessive power dissipation at high currents causing a thermal runaway. At a temperature of 40 K the sheet resistance drops to 20.9 µO/sq giving a lower limit for the residual resistance ratio of 100. Continuous currents of 13 A can be applied, resulting in a simulated magnetic field gradient of 144 T m-1 at the ion position, which is 125 µm from the trap surface for the particular anti-parallel wire pair in our design
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Fabrication of surface ion traps with integrated current carrying wires enabling high magnetic field gradients
No full textA major challenge for quantum computers is the scalable simultaneous execution of quantum gates. One approach to address this in trapped ion quantum computers is the implementation of quantum gates based on static magnetic field gradients and global microwave fields. In this paper, we present the fabrication of surface ion traps with integrated copper current carrying wires embedded inside the substrate below the ion trap electrodes, capable of generating high magnetic field gradients. The copper layer's measured sheet resistance of 1.12 mO/sq at room temperature is sufficiently low to incorporate complex designs, without excessive power dissipation at high currents causing a thermal runaway. At a temperature of 40 K the sheet resistance drops to 20.9 µO/sq giving a lower limit for the residual resistance ratio of 100. Continuous currents of 13 A can be applied, resulting in a simulated magnetic field gradient of 144 T m-1 at the ion position, which is 125 µm from the trap surface for the particular anti-parallel wire pair in our design
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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
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