Modelling laser milling of microcavities for the manufacturing of DES with ensembles

A set of designed experiments, involving the use of a pulsed Nd:YAG laser system milling 316L Stainless Steel, serve to study the laser-milling process of microcavities in the manufacture of drug-eluting stents (DES). Diameter, depth, and volume error are considered to be optimized as functions of the process parameters, which include laser intensity, pulse frequency, and scanning speed. Two different DES shapes are studied that combine semispheres and cylinders. Process inputs and outputs are defined by considering the process parameters that can be changed under industrial conditions and the industrial requirements of this manufacturing process. In total, 162 different conditions are tested in a process that is modeled with the following state-of-the-art data-mining regression techniques: Support Vector Regression, Ensembles, Artificial Neural Networks, Linear Regression, and Nearest Neighbor Regression. Ensemble regression emerged as the most suitable technique for studying this industrial problem. Specifically, Iterated Bagging ensembles with unpruned model trees outperformed the other methods in the tests. This method can predict the geometrical dimensions of the machined microcavities with relative errors related to the main average value in the range of 3 to 23%, which are considered very accurate predictions, in view of the characteristics of this innovative industrial task.This work was partially funded through Grants fromthe IREBID Project (FP7-PEOPLE-2009-IRSES- 247476) of the European Commission and Projects TIN2011- 24046 and TECNIPLAD (DPI2009-09852) of the Spanish Ministry of Economy and Competitivenes

Low loss dielectric mirrors for optical cavities applications

Cavity-based single-photon emitters possess great potential in many quantum applications. Fabry-Perot cavities are an especially good candidate for these applications in order to provide the high-Q cavities necessary for efficient coupling. To assure strong coupling in the cavity, very high reflectance dielectric mirrors are required. Achieving this means overcoming several technical challenges in order to minimize the optical losses in the dielectric layers. This research work explores the potential of several dielectric materials and physical vapour deposition methods to fabricate high reflectance mirrors in the visible region. Single layer material characterisation results showed extinction coefficients below 10-5 and a surface roughness below 1 nm for metal oxides deposited by ion assisted and plasma assisted processes. A reflectance superior to 99.9 % was obtained for TiO2/SiO2, ZrO2/SiO2 and Nb2O5/SiO2 multilayer mirrors deposited using ion assisted E-beam, plasma assisted and microwave assisted sputtering methods. A surface roughness of 0.3 to 0.5 nm was obtained for ZrO2/SiO2 and Nb2O5/SiO2 multilayer mirrors deposited using plasma assisted and microwave assisted sputtering methods. Scatter losses of 200 ppm were obtained for TiO2/SiO2 deposited using ion assisted E-beam deposition. Micron sized TiO2/SiO2 and ZrO2/SiO2 mirrors were achieved on curved glass templates by Ion assisted E-beam deposition

Silicon vacancy colour centres in diamond: coherence properties & quantum control

The scope of this thesis is to investigate the coherence properties of negatively charged silicon vacancy centres (SiV) in diamond and to establish techniques to coherently control their quantum state, aiming at applications in quantum information processing. For the first time, using coherent population trapping (CPT) in magnetic fields, we determine the centres ground state electron spin coherence time to amount to 45 ns at 4.2 K. To investigate the limiting processes, we realize a confocal microscope operating in a dilution refrigerator at temperatures as low as 12 mK. Using further CPT and optical pumping experiments, we identify a resonant coupling to a spin bath as a source of decoherence persisting at millikelvin temperatures, in addition to phonon-mediated processes at higher temperatures. Using Raman transitions we realize optical Rabi oscillations, Ramsey interference and spin echo measurements to validate these findings and simultaneously demonstrate coherent control at 12 mK. We further extend these techniques to achieve full resonant and Raman-based all-optical coherent control using laser pulses as short as 1ps, reaching exceptional control speeds. Finally, we demonstrate for the first time coherent manipulation of SiV ensembles using stimulated Raman adiabatic passage and Raman absorption of a weak signal aided by a strong control pulse as a proof-of-principle experiment towards a SiV-based Raman quantum memory.In dieser Arbeit werden die Kohärenzeigenschaften negativ geladener Silizium-Fehlstelle-Farbzentren (SiV) in Diamant untersucht und Techniken zu deren kohärenter Kontrolle entwickelt, mit dem Ziel sie für die Quanteninformationsverarbeitung nutzbar zu machen. Mittels "coherent population trapping" (CPT) in Magnetfeldern wird erstmals die Elektronenspin-Kohärenz einzelner SiV- bestimmt und eine Kohärenzzeit von 45 ns bei 4.2K ermittelt. Weitere Untersuchungen in einem Verdünnungskryostat bei Temperaturen von bis zu 12mK identifizieren eine resonante Kopplung an ein Spinbad als wichtigste Quelle von Dekohärenz im Millikelvin-Regime, während bei höheren Temperaturen zusätzlich Phononen-assistierte Prozesse relevant werden. Dies wird durch Raman-basierte optische Rabi-, Ramsey- und Spin Echo-Experimente bestätigt, welche gleichzeitig kohärente Kontrolle bei 12mK demonstrieren. Unter Verwendung ultrakurzer Laserpulse werden diese Techniken schließlich erweitert und erstmalig resonante sowie Raman-basierte optische kohärente Kontrolle auf der Pikosekunden-Skala realisiert. Abschließend wird auch die kohärente Manipulation von SiV--Ensembles untersucht und kohärenter Populationstransfer mittels stimuliertem adiabatischem Raman-Transfer sowie Raman-Absorption eines schwachen Signals mittels eines starken Kontrollfelds demonstriert. Diese Experimente bilden die Grundlage für die Entwicklung eines SiV-basierten optischen Quantenspeichers

Quantum dots for photonic quantum information technology

The generation, manipulation, storage, and detection of single photons play a central role in emerging photonic quantum information technology. Individual photons serve as flying qubits and transmit the quantum information at high speed and with low losses, for example between individual nodes of quantum networks. Due to the laws of quantum mechanics, quantum communication is fundamentally tap-proof, which explains the enormous interest in this modern information technology. On the other hand, stationary qubits or photonic states in quantum computers can potentially lead to enormous increases in performance through parallel data processing, to outperform classical computers in specific tasks when quantum advantage is achieved. Here, we discuss in depth the great potential of quantum dots (QDs) in photonic quantum information technology. In this context, QDs form a key resource for the implementation of quantum communication networks and photonic quantum computers because they can generate single photons on-demand. Moreover, QDs are compatible with the mature semiconductor technology, so that they can be integrated comparatively easily into nanophotonic structures, which form the basis for quantum light sources and integrated photonic quantum circuits. After a thematic introduction, we present modern numerical methods and theoretical approaches to device design and the physical description of quantum dot devices. We then present modern methods and technical solutions for the epitaxial growth and for the deterministic nanoprocessing of quantum devices based on QDs. Furthermore, we present the most promising concepts for quantum light sources and photonic quantum circuits that include single QDs as active elements and discuss applications of these novel devices in photonic quantum information technology. We close with an overview of open issues and an outlook on future developments.Comment: Copyright 2023 Optica Publishing Group. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modifications of the content of this paper are prohibite

Report / Institute für Physik

The 2017 Report of the Physics Institutes of the Universität Leipzig provides an overview of the structure and research activities of the three institutes. We are happy to announce that Prof. Dr. Caudia Schnohr from Universität Jena will join the Felix Bloch Institute for Solid State Physics beginning 2019 filling the vacant position in the department for Solid State Optics. Dr. Johannes Deiglmayr from ETH Zurich will establish an independent department for Quantum Optics at the same institute

Report / Institute für Physik

The 2017 Report of the Physics Institutes of the Universität Leipzig provides an overview of the structure and research activities of the three institutes. We are happy to announce that Prof. Dr. Caudia Schnohr from Universität Jena will join the Felix Bloch Institute for Solid State Physics beginning 2019 filling the vacant position in the department for Solid State Optics. Dr. Johannes Deiglmayr from ETH Zurich will establish an independent department for Quantum Optics at the same institute