Ultraclean carbon nanotubes and superconducting coplanar resonators: Materials, nano-electromechanics, and few-electron systems

Scope of the thesis was the investigation of nano-electromechanical properties of carbon nanotubes, the preparation of a reliable fabrication process and measurement setup for coplanar waveguides, and work towards a combination of both systems. Regarding the properties of carbon nanotubes, numerical transmission calculations were performed for various chiralities in a parallel magnetic field to obtain a more detailed understanding of the transport spectrum. In addition, the numerical transmission calculations are compared to the experimental data and an analytic model. The coupling of electrons and vibrons of the longitudinal stretching mode was observed in a suspended carbon nanotube. Analysis led to a magnetic field dependent Franck-Condon coupling factor. Regarding coplanar waveguides, first measurements of niobium superconducting quarter wavelength resonators were presented; internal quality factors up to 240000 were observed. The low temperature behavior of the resonance frequency and the internal quality factor were both well described by changes in the kinetic inductance fraction and the loss due to two-level systems present in the substrate material

Classically entangled optical beams for high-speed kinematic sensing

Tracking the kinematics of fast-moving objects is an important diagnostic tool for science and engineering. Existing optical methods include high-speed CCD/CMOS imaging, streak cameras, lidar, serial time-encoded imaging and sequentially timed all-optical mapping. Here, we demonstrate an entirely new approach to positional and directional sensing based on the concept of classical entanglement in vector beams of light. The measurement principle relies on the intrinsic correlations existing in such beams between transverse spatial modes and polarization. The latter can be determined from intensity measurements with only a few fast photodiodes, greatly outperforming the bandwidth of current CCD/CMOS devices. In this way, our setup enables two-dimensional real-time sensing with temporal resolution in the GHz range. We expect the concept to open up new directions in photonics-based metrology and sensing.Comment: v2 includes the real-time measurement from the published version. Reference [29] added. Minor experimental details added on page

Zur Ressourcenproduktivität von spurgeführten Hochgeschwindigkeitsverkehrssystemen: Ein Vergleich von ICE und Transrapid. Eine gemeinsame Studie des Lehrstuhls für Technikwirkungs- und Innovationsforschung der Universität GH Kassel und des Wuppertal-Instituts

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Quantum-limited measurements of optical signals from a geostationary satellite

The measurement of quantum signals that traveled through long distances is of fundamental and technological interest. We present quantum-limited coherent measurements of optical signals, sent from a satellite in geostationary Earth orbit to an optical ground station. We bound the excess noise that the quantum states could have acquired after having propagated 38600 km through Earth's gravitational potential as well as its turbulent atmosphere. Our results indicate that quantum communication is feasible in principle in such a scenario, highlighting the possibility of a global quantum key distribution network for secure communication.Comment: 8 pages (4 pages main article, 4 pages supplementary material), 9 figures (4 figures main article, 5 figures supplementary material), Kevin G\"unthner and Imran Khan contributed equally to this wor

Telecommunication Economics — Summary on the Dagstuhl Perspectives Seminar No. 08043

The telecommunications sector and the Internet section of Internet Service Providers (ISP) have become a dynamic key area for the economic development of industrialized nations in the world. It is in constant evolution. Because of intense competition, telecommunications companies and ISPs are forced to diversify their offers and thus to propose an increasing number of services. However, economic analysis often ignores important technical aspects of telecommunications and is not aware of new developments. Engineering models often ignore economic factors. Thus, the design and deployment of future networks that incorporate new services are subject to uncertainties such as equipment and capacity prices (due to technological innovation), demand and supply for services (due to competition). Seeing leading researchers bringing together with various backgrounds, all working on innovative aspects of technical, techno-economic, social, and regulatory issues, lead to the following four main areas that have been partially tackled in an integrated manner: Architectural side, Social side, Economic and business side, and Regulatory side