1,721,028 research outputs found
Nanowire-based Quantum Photonics
No full textIn this thesis work, I studied individual quantum dots embedded in one-dimensional nanostructures called nanowires. Amongst the effects given by the nanometric dimensions, quantum dots enable the generation of single light particles: photons. Single photon emitters and detectors are central building blocks of future communication technologies. As the miniaturization in electronics is driving towards the quantum limit, we envision future telecommunication as based on single photons. Single photons enable the use of quantum properties of light to encode information and share it with unbreakable security provided by quantum cryptography. Based on the principle that a single photon cannot be cloned and that its quantum state cannot be observed without altering it the information that the photon is carrying, a single particle of light represents the ideal mean of transportation for future secure telecommunication. During my work, nanowires have been tailored into waveguides providing directional propagation along the nanostructure that out-couples to the macroscopic world with negligible losses. The optical properties of the quantum dots have been explored through photoluminescence spectroscopy and improved in order to obtain a pure flux of single photons. Simultaneously, the material composition and shape of the nanowire have been designed to achieve efficient collection of these photons. Nanowires are tailored into waveguides providing directional propagation along the nanostructure that out-couples to the macroscopic world with negligible losses. This system we developed can be seen as an analogue of an nano optical fiber where photons are propagating one at a time. Several optical properties of the emitted single photons have been analyzed and subsequently optimized such as the temporal emission statistics, the shape and dispersion of the energy spectrum and the spatial emission profile. In addition, we demonstrated the possibility of creating an excitation in the quantum dot and translate this excitation into an electrical signal transmitted along the nanowire, thereby detecting the generation of individual excitations in the nanostructure.Kavli Institute of Nanoscience DelftApplied Science
Quantum Dots in Vertical Nanowire Devices
No full textThe research described in this thesis is aimed at constructing a quantum interface between a single electron spin and a photon, using a nanowire quantum dot. Such a quantum interface enables information transfer from a local electron spin to the polarization of a photon for long distance readout. Important aspects for the realization of such a device are the optical quality of the quantum dot and access to the optical polarization. In this thesis, we demonstrate high quality nanowire quantum dots and observe spin memory. By embedding them in a vertical nanowire device, we are able to isolate a single electron on the dot, while maintaining access to the intrinsic polarization properties of the nanowire quantum dot. These results demonstrate that quantum dots in vertical nanowire device are promising as an optical interface for single electron spins.Kavli Institute of NanoscienceApplied Science
Towards Fast Light at the Single Photon Level
No full textApplied PhysicsKavli Institute of Nanoscience DelftApplied Science
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
Superconducting detector dynamics studied by quantum pump-probe spectroscopy
Get PDFWe explore the dynamics of superconducting single-photon detectors (SSPDs) on the picosecond time-scale using a correlated photon-pair source based on spontaneous parametric downconversion (SPDC), corresponding to a pump-probe experiment at the single-photon level. We show that the detector can operate in a regime where the two-photon detection probability is orders of magnitude larger than the single-photon detection probability. The characteristic relaxation time-scale of the out-of-equilibrium hot-spot is found to be ? 15?ps. Our measurement technique is an effective tool to study fast two-photon processes, without requiring a power-dependence measurements to determine the number of photons involved.Quantum NanoscienceApplied Science
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
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