1,720,993 research outputs found
Repeater-based quantum communication with advanced optical encoding
Get PDFQuantenkommunikation ermöglicht es Nachrichten informationstheoretisch beweisbar sicher zu verschlüsseln, wobei die Datenübertragungsraten über große Distanzen durch Verlusteund Fehler stark reduziert sind. Diese niedrigen Übertragungsraten können durch den Einsatz von Quantenrepeatern, die die Gesamtdistanz in mehrere kleine Teildistanzenaufteilen, verbessert werden. In dieser Arbeit werden zwei unterschiedliche Ansätze von Quantenrepeatern untersucht. Bezüglich speicherbasierter Quantenrepeater schlagen wir ein neues Schema vor, das auf der Interferenz einzelner Photonen basiert und durch das kürzlich vorgestellte Twin-field Quantenschlüsselaustauschprotokoll inspiriert wurde. Außerdem werden erreichbare Datenübertragungsraten geheimer Schlüssel, die bereits mit kleinen Quantenrepeatern auf unterschiedlichen physikalischen Plattformen erzielt werden können, auf Grundlage von experimentell vorgegebenen Parametern berechnet. Des Weiteren werden auch größere Quantenrepeater untersucht, wobei wir das Dephasieren der Quantenspeicher exakt berechnen. Damit werden dann auch Übertragungsraten geheimer Schlüssel für verschiedene speicherbasierte Quantenrepeater berechnet und miteinanderverglichen. Bezüglich des alternativen Ansatzes eines Quantenrepeaters basierend auf Quantenfehlerkorrekur stellen wir zunächst eine experimentell einfachere Möglichkeit, die auf linearer Optik beruht, vor, um das Fehlersyndrom eines GKP Codes zu bestimmen.Diese Methode führt zusätzlich zu geringeren Fehlerraten und wir diskutieren auch Grenzen der linearen Optik. Schlussendlich wenden wir diese Methoden im Kontext eines auf GKP Qudits basierenden Quantenrepeaters an. Dabei zeigt sich, dass es für in der näheren Zukunft experimentell sinnvolle Parameter besser ist GKP Qubits anstatt höherdimensionaler GKP Qudits zu nutzen.Quantum communication makes it possible to encrypt messages providing informationtheoretic security, but suffers from a large decrease of the transmission rate for larger distances due to loss and errors. These low rates can be increased by employing quantum repeaters which divide the total distance into multiple smaller segments and this thesis deals with two different approaches for such quantum repeaters. Regarding quantum repeaters employing memories we propose a new scheme based on single-photon interference inspired by the recently discovered twin-field quantum key distribution protocol. Furthermore, we calculate secret-key rates obtainable in small-scale repeaters with different physical platforms using realistic parameters obtained from experimentalists and we also perform an analysis for larger repeaters where we calculate the memory dephasing exactly and compare secret-key rates for different memory-based repeater proposals. Concerning the repeater approach employing solely quantum error correction we propose experimentally simpler methods of obtaining the error syndrome for GKP codes based on linear optics also leading to an improved performance and we also discuss limitations of linear optics. We then apply these methods of GKP error correction to a repeater employing GKP qudits. There we find that for experimentally reasonable parameters in the near future it is better to use GKP qubits instead of high-dimensional GKP qudits.Getrennte Zählungen ; Illustrationen, Diagramm
Optische Implementierungen von Quantenfehlerkorrekturprotokollen
No full textWe investigate the implementation of various quantum-optical codes, with attention given to the experimentally-relevant case of amplitude damping.
A new fidelity measure is developed by exploring the resulting non-orthogonality of a code's input alphabet after the action of undesired error mechanisms. With the use of this new quantity, we are able to reproduce, in a different manner, a statement concerning the impossibility of implementing quantum error correction when considering a set of operations restricted to Gaussian resources.
Furthermore, for a particular code designed to protect qubits encoded in continuous-variable carrier states, a novel analysis of the code performance is presented under different operating regimes.
Finally, we also investigate an altogether different approach to circumvent amplitude damping in photonic qubits, with a potential application to quantum key distribution.Wir untersuchen die Umsetzung von verschiedenen quantenoptischen Fehlerkorrektur-Protokollen, mit Schwerpunkt auf dem experimentell relevanten Photonenverlust.
Durch die Untersuchung der nicht-Orthogonalit\at des Eingabealphabetes nach der Einwirkung von Fehlermechanismen wird ein neues Ma{\ss} f\ur die Wiedergabetreue des Codes entwickelt. Mit dem Einsatz dieser neuen Gr\o{\ss}e sind wir in der Lage eine Aussage \uber die Unm\oglichkeit einer Quanten-Fehlerkorrektur auf eine andere Weise zu reproduzieren, wenn man die Anwendung ausschlie{\ss}lich auf Gau{\ss}-Ressourcen beschr\ankt.
Des weiteren, f\ur ein bestimmtes Protokoll, das Qubits durch eine Codierung in Zust\anden mit kontinuierlichen Variablen sch\utzt, wird eine neuartige Analyse der Leistung des Codes in verschiedenen Regimen pr\asentiert.
Im letzten Teil der Arbeit schlagen wir eine neue Methode vor die Amplitudend\ampfung in photonischen Qubits zu umgehen. Diese Methode ist potentiell in der Quantenschl\usselverteilung anwendbar
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
Teleportationsbasierte Implementierungen von quantenoptischen Gattern mit kontinuierlichen Variablen
Get PDFThis thesis addresses the following question:
How can one deterministically implement a given quantum evolution with current quantum optical elements?
This question is closely related to the following topics:
quantum computing with continuous and discrete variables, quantum control,
simulation of Hamiltonians, and any situation when a given quantum mechanical state is to be
transformed in a deterministic fashion.
In this work, a systematic and efficient method for implementing an arbitrary
quantum mechanical evolution is derived, including various explicit ways for its construction.
Existing techniques for obtaining weak nonlinear interactions such as the Kerr interaction
are usually based on some naturally occurring, nonlinear, intensity-dependent light-matter interaction [Boy08].
Alternatively, in this thesis, we present effective nonlinearities based on measurements.
These measurement-induced nonlinearities are initially also weak.
Nonetheless, we will present methods to optimize and amplify the corresponding
nonlinear evolutions. This way, in principle, even relatively strong nonlinearities can be realized,
as well as, ultimately, universal quantum computation -- for instance, by means of
a complete Kerr gate.Diese Arbeit behandelt folgende Frage:
Wie kann man deterministisch eine gegebene Quantenevolution mit den heutigen quantenoptischen Elementen implementieren?
Die Fragestellung ist eng verbunden mit folgenden Themenkomplexen:
Quantenberechnungen mit kontinuierlichen und diskreten Variablen, Quantenkontrolle, Simulierung von Hamilton-Operatoren sowie die allgemeine Situation, wenn gegebene quantenmechanische Zustände deterministisch transformiert werden sollen.
In der vorliegenden Arbeit wird eine systematische und effiziente Methode zur kontrollierten Implementierung von beliebigen quantenmechanischen Evolutionen hergeleitet, einschliesslich verschiedener expliziter Konstruktionsmöglichkeiten.
Vorhandene Techniken zur Implementierung von schwachen nichtlinearen Wechselwirkungen -- wie zum Beispiel die sog. Kerr-Wechselwirkung -- sind üblicherweise mediumsbasiert, d.h. sie werden realisiert durch eine natürliche nichtlineare, intensitätsabhängige Wechselwirkung zwischen Licht und Materie [Boy08].
Dazu alternativ präsentieren wir in dieser Arbeit messungsbasierte Nichtlinearitäten im Gegensatz zu den Nichtlinearitäten in Medien.
Diese messungsbasierten Nichtlinearitäten sind zunächst ebenfalls schwach.
Allerdings zeigen wir auch Ansätze und Techniken, um die entsprechenden Implementationen zu optimieren und zu verstärken. Damit können dann im Prinzip auch relativ starke Nichtlinearitäten realisiert werden, die letztlich auch das universelle Quantenrechnen ermöglichen -- wie zum Beispiel mit Hilfe eines kompletten Kerr-Gatters
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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