1,720,976 research outputs found
Replication Data for "A Phase Microscope for Quantum Gases"
No full textExperimental images and associated analysis codes used to generate the figures from both main text and supplementary material. Data presented in arXiv preprint https://arxiv.org/abs/2410.10611
A phase microscope for ultra-cold quantum gases
No full textCoherence properties play a central role in quantum systems and are fundamental to phenomena such as superfluidity and superconductivity. Ultracold gases in optical lattices provide an versatile platform for quantum simulation, allowing precise control to explore coherence properties that underlie complex quantum phenomena.
In this thesis, we investigate the coherence properties of an ultra cold Bose gas in a two-dimensional optical lattice, focusing on phase coherence and fluctuations across the Berezinskii-Kosterlitz-Thouless (BKT) phase transition. We utilize matter-wave microscopy with an optical matter-wave lens to magnify the atomic wavefunction, enabling us to image the density distribution with single-site resolution.
The ability to turn off interaction allows us to measure a coherent wavefunction released from a lattice. This reveals the two-dimensional Talbot effect, where the periodic density modulations from the lattice is self-imaged and we capture in-situ images of these periodic revivals. The strength of the revivals are a direct measure for the spatial coherence of the system. Furthermore, we present the implementation of a phase microscope for ultra cold quantum gases. The phase microscope enables us to extract the relative phases on single lattice sites. We measure the phase correlation towards the BKT phase transition and obtain a critical exponent for the algebraic decay in our system. The matter-wave and phase microscopy techniques presented here offer an approach towards exploring coherence in strongly correlated quantum systems, providing full spatial resolution and potential insights into phase transitions and novel quantum phases
Ein Materiewellen-Mikroskop für Lithium-Atome in einem durchstimmbaren optischen Gitter
No full textUltracold gases in optical lattices are a pristine experimental platform for quantum simulation of complex many-body systems as they come with a high degree of control and a wide range of accessible observables. The advent of quantum gas microscopes has revolutionized the access to quantum many-body systems by detecting and addressing single particles on single lattice sites. However, they are limited to 2-dimensional (2D) systems and suffer from parity projection due to light-assisted collisions. A complementary approach is the so-called matter-wave microscopy or quantum gas magnification, where the atomic density distribution is magnified via matter-wave optics before taking absorption images with sub-lattice site resolution.
In this thesis, we report on the construction of a matter-wave microscope for ultracold 7Li-atoms in optical lattices. Within the course of this thesis, we adapted the experimental apparatus that was formerly used for experiments with the fermionic isotope 6Li, to create Bose-Einstein condensates of ca. 1 × 10^5 7Li-atoms within a cycle time of ca. 14 s. To this end, we implemented a multi-frequency 2D-MOT scheme and set up an optically plugged magnetic quadrupole trap as well as a novel dipole trap setup, that can simultaneously be used to create optical lattices with dynamically tunable, yet passively stable geometry of the lattice structure. The interference of three laser beams is suppressed by detuning their frequencies and then pairwisely reestablished by imprinting sidebands onto each beam. This setup allows us to use the same beams as a dipole trap that we also employ as a matter-wave lens for the magnification of the density distribution in the matter-wave microscopy. Via a quarter-period evolution in the harmonic trap, the initial positions of the atoms are mapped onto their momenta. A subsequent time of free expansion results in a Fourier transform back to the initial density distribution but with a magnification M that is typically on the order of M ≈ 24 for our parameter settings. We use this technique to study the matter-wave Talbot effect in coherent systems, which in the future will give us access to the g1 correlation function.Ultrakalte Quantengase in optischen Gittern bieten vielseitig einsetzbare Möglichkeiten zur Quantensimulation komplexer Vielteilchensysteme. Sie bestechen dabei durch einen hohen Grad an Kontrolle über das Modellsystem und den Zugang zu einer großen Anzahl von Observablen. Durch die Einführung von Quantengasmikroskopen mit der Möglichkeit, einzelne Teilchen an einzelnen Gitterplätzen zu detektieren und gezielt zu manipulieren, wurde der Zugang zu quantenmechanischen Vielteilchensystemen revolutioniert. Allerdings beschränkt sich dieser Zugang auf zweidimensionale Systeme und Licht-assoziierte Stöße führen dazu, dass nur die Parität der Besetzung auf einem Gitterplatz gemessen werden kann. Ein hierzu komplementärer Ansatz besteht in der sogenannten Materiewellen-Mikroskopie oder auch Quantengasvergrößerung. Hierbei wird die atomare Dichteverteilung mit Hilfe von Materiewellen-Optik vergrößert, bevor sie in einer Absorptionsabbildung mit Sub-Gitterplatzauflösung abgebildet wird
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In dieser Dissertation wurde ein Experiment zur Materiewellen-Mikroskopie ultrakalter 7Li-Atome in optischen Gittern aufgebaut. Die experimentelle Apparatur, die vormals zum Kühlen des fermionischen Isotops 6Li benutzt wurde, wurde im Rahmen dieser Arbeit angepasst, sodass sie nun wiederholt Bose-Einstein-Kondensate bestehend aus 1 × 10^5 7Li-Atomen innerhalb von 14 s erzeugen kann. Hierfür wurde eine multifrequenz-basierte 2D-MOT entwickelt und eine magnetische Quadrupolfalle in Betrieb genommen. Das Einstrahlen eines repulsiven Laserstrahls verhindert hierbei Majorana-Verluste im Fallenzentrum. Darüberhinaus wurde eine neuartige Dipolfalle errichtet, die auch als optisches Gitter verwendet werden kann. Hierfür werden zunächst drei Laserstrahlen in ihrer Frequenz zueinander verstimmt, sodass sie nicht miteinander interferieren. Anschließend sorgt das Aufmodulieren von Frequenz-Seitenbändern dafür, dass die Interferenz paarweise wiederhergestellt wird. Hierdurch kann die Geometrie der entstehenden Gitterstruktur dynamisch verändert werden, wobei die Geometrie dennoch passiv stabil bleibt. Dieses Lasersystem nutzen wir unter anderem als optische Dipolfalle für die Materiewellen-Mikroskopie. Wir halten die Atome für eine viertel Periode in der durch die Dipolfalle realisierten harmonischen Falle, was dazu führt, dass der anfängliche Ort der Atome durch eine Fourier-Transformation in einen Impuls umgewandelt wird. Eine anschließende freie Expansion ermöglicht eine Rücktransformation zur ursprünglichen Dichteverteilung, wobei diese um einen Faktor M vergrößert wurde. Für typische experimentelle Parameter in unserem System ist diese Vergrößerung M ≈ 24. Mit dieser Technik studieren wir den sogenannten Materiewellen-Talbot-Effekt. Dieser tritt in kohärenten Systemen auf und wird es uns in Zukunft ermöglichen, Rückschlüsse auf die g1-Korrelationsfunktion zu ziehen
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
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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