1,720,966 research outputs found
Kerr-enhanced optomechanics
Full text linkThe pursuit of ground state cooling a mechanical mode has been of significant interest for its fundamental relevance to numerous quantum science and technology applications. In recent years, optomechanical backaction cooling protocols have successfully achieved the motional quantum ground state of a mechanical oscillator in the resolved sideband regime, i.e. when the mechanical resonance frequency is significantly larger than the cavity decay rate. However, as the size of these mechanical systems increases, their natural frequency generally decreases, pushing them into the unresolved sideband regime. Backaction cooling becomes less effective in this regime, limiting the ability to cool the mechanical mode to its ground state.
In this thesis, we theoretically study a novel optomechanical setup, where a nonlinear cavity and a mechanical cantilever are inductively coupled. Despite being initially proposed to achieve single-photon coupling strengths, this system has the particularity of being able to more efficiently backaction cool a mechanical mode in the unresolved sideband regime. We will demonstrate that the intrinsic nonlinearity of the cavity results in an enhancement of the cooling capabilities in the sideband unresolved regime as experimentally shown in D. Zoepfl et al. (PRL, 2023). The above arises due to the increased asymmetry between the cooling and heating processes, thereby improving the cooling efficiency
Novel Applications of Nonreciprocal Quantum Amplifiers
Full text linkThe implementation of quantum-limited amplifiers has been a necessity for the high-fidelity processing of signals involving few weak photons, commonly encountered in experiments involving superconducting microwave electronics. The need to protect sensitive quantum systems during these experiments demands the use of devices capable of directionally routing the noisy signals from these amplifiers away from the quantum system under observation, which is accomplished by breaking the symmetry of reciprocity. To reduce losses and improve fidelity, both characteristics may be realised in a single device: the nonreciprocal quantum amplifier. In this dissertation, we explore uses for nonreciprocal quantum amplifiers that go beyond these signal processing applications. These applications will depend on the quantum nature of the amplifier, and so cannot be realised using components operating in the classical regime. Two different utilisations are considered in this work. We first examine the ability of nonreciprocal amplifiers to entangle their output signals and find that not only does directional signal transmission not inhibit the formation of entangled states, but it simultaneously allows for the routing of unwanted noise away from these outputs. This allows for the generation of high-fidelity propagating entangled states in noisy channels. The second project is motivated by a desire to improve the efficiency of measuring the state of a superconducting transmon qubit. The measurement requires the use of a microwave resonator to convert information about the qubit state into a microwave photon signal, which must then be passed to a quantum-limited preamplifier. While it has been demonstrated that using a nonreciprocal preamplifier improves the measurement efficiency, it is still reduced due to the presence of extra wiring with the resonator. We therefore consider a case where the same device acts as both the measurement resonator and the nonreciprocal preamplifier. We demonstrate that the amplification allows for a robust and highly efficient qubit measurement, while the nonreciprocity concurrently prevents excess backaction on the qubit
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
Kohärenter Transport durch nanoelektromechanische Systeme
No full textDie Untersuchung von kohärentem Transport durch nanoelektromechanische Systeme (NEMS) steht im Fokus dieser Arbeit. NEMS stellen Bauteile dar, bei denen ein quantenmechanisches Transportsystem an die Freiheitsgrade eines mechanischen Systems koppelt. Damit ist eine Untersuchung der Elektron-Phonon Wechselwirkung in einer Nicht-Gleichgewichtsumgebung möglich. Im Allgemeinen wird bei der semi-klassischen Betrachtung dieser mechanisch-elektrischen Systeme eine adiabatische Näherung durchgeführt. In dieser Näherung geht man davon aus, dass sich die Elektronen die durch das System tunneln deutlich schneller bewegen als der Oszillator, d.h. der Oszillator spürt nur ein effektives von den Elektronen verursachtes Potential, während er seine Position im Gegensatz zu den Elektronen nur langsam verändert. Die interessantesten Phänomene zeigen sich jedoch, wenn sich die Elektronen und der Oszillator sich auf einer ähnlichen Zeitskala bewegen. Im Rahmen dieser Arbeit wird die Dynamik des Oszillators in adiabatischer und in nicht-adiabatischer Näherung untersucht. Um Zugang zu den mechanischen Eigenschaften zu erlangen kann die Methodik der Feynman-Vernon Influenz Funktionale genutzt werden. Wir konzentrieren uns auf zwei elektronische Modellsysteme -- das Ein- und Zwei-Level System -- die linear an eine einzige bosonische Mode koppeln. Wir nutzen den Greenschen Formalismus zur Berechnung der elektronischen Eigenschaften, dieser bietet, in seiner Erweiterung durch Keldysh, Möglichkeiten Nichtgleichgewichts - Prozesse zu beschreiben. Die Dynamik für einen Oszillator im elektronischen Zwei-Level System zeigt ein nicht-triviales Verhalten, es treten beispielsweise Grenzzyklen und Bistabilitäten auf. Wir untersuchen ausführlich die auftretenden Effekte mit Methoden für nichtlineare dynamische Syteme. Zudem erfolgt die Berechnung von Strom und Rauschen, beides Eigenschaften die experimentell zugänglich sind. Eine weitere Besonderheit der verwendeten Methode ist, dass keine störungstheoretische Behandlung der Kopplung zwischen dem Quantensystem und den elektronischen Anschlüssen erfolgt. Zudem zeigen wir, dass sich unsere nicht-adiabatische Methodik ohne weiteres auf bestimmte Systeme übertragen lässt. Dazu nutzen wir das Modell eines elektronischen Transportsystems mit einem elektronischen Level, dass an einen großes Ensemble von Spins koppelt, und dem Einfluss eines externen Magnetfeldes unterliegt. Das Spin Ensemble kann durch einen großen effektiven Spin beschrieben werden, für den eine semi-klassische Beschreibung möglich ist. Dabei werden die Quantenfluktuationen des Systems als klein angesehen und die Wechselwirkung zwischen den Spin- Systemen im Rahmen einer Meanfield-Näherung beschrieben.In this thesis we compare the semiclassical description of nanoelectromechanical systems (NEMS) within and beyond the Born-Oppenheimer approximation. NEMS enable the detailed study of the interaction between electrons, tunneling through a nano-scale device, and the degrees of freedom of a mechanical system. We work in the semiclassical regime where an expansion around the classical path is performed. The advantage of this method is, that it is nonperturbative in the system-leads coupling, because the exact electronic solutions are included. We develop a nonadiabatic approach, where we can treat the oscillator and the electrons on the same time-scale without further constrains. The considered NEMS models contain a single phonon (oscillator) mode linearly coupled to an electronic few-level system in contact with external particle reservoirs (leads). Using Feynman-Vernon influence functional theory, we derive a Langevin equation for the oscillator's trajectories. A stationary electronic current through the system generates nontrivial dynamical behaviour of the oscillator, even in the adiabatic regime. We present a detailed prescription of the oscillator's phase space and investigate the observed dynamical features with methods for nonlinear dynamical systems. The backaction of the oscillator onto the electronic properties is studied as well. For the cases of one and two coupled electronic levels, we discuss the differences between the adiabatic and the nonadiabatic regime of the oscillator dynamics. Furthermore, we apply the developed methods to a single-level system which is anisotropically coupled to a large spin under the influence of an external magnetic field. Here, the semiclassical treatment of the large spin's dynamics is included within a mean-field approach for the spin-spin interaction. This system possess rich dynamical properties, like self-sustained and chaotic oscillations. We investigate the system in the nonequilibrium regime for high external bias, where we can compare our nonadiabatic method to a rate equation approach, which is perturbative in coupling to the leads. Additionally, we study the system in the low bias case, where the dynamics are even richer as in the infinite bias case
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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