Polarization-preserving quantum frequency conversion for trapped-atom based quantum networks

The scope of this thesis is the development of efficient and low-background polarization- preserving quantum frequency converters (PPQFC) and their integration into trapped-atom based quantum network nodes to demonstrate building blocks of a quantum network (QN). We constructed four PPQFC devices to transduce the emission wavelengths of single trapped 40Ca+-ions at 854 nm and neutral 87Rb-atoms at 780 nm to the low-loss telecom bands between 1260 nm and 1625 nm. Upon the conversion process, the quantum information encoded in the photon polarization has to be preserved. To this end, we rely on difference frequency generation in ridge waveguides, which are inserted into polarization interferometers arranged in Sagnac- or Mach-Zehnder-type configuration. For the conversion of single and entangled photons we achieved external device efficiencies between 26.5 % and 57.4 %, low background levels, which allow for signal-to-background ratios above 20, and process fidelities > 99.5 %. Employing the PPQFC devices, we were able to demonstrate several key elements of long-distance QNs: photon-photon entanglement over 40 km of fiber via 2-step QFC with a fidelity of 98.9 %, ion-telecom-photon entanglement with high fidelities up to 97.8 %, an atom-to-telecom-photon state transfer, and the distribution of atom-photon entanglement over 20 km of fiber with a fidelity of 78.9 %. These results hold great promise to extend small QNs with ≥ 2 nodes to a metropolitan scaleIn dieser Arbeit werden effiziente und hintergrundarme polarisationserhaltende Quan- tenfrequenzkonverter (PPQFC) entwickelt und in Quantennetzwerkknoten basierend auf gefangenen Atomen integriert, um Bausteine eines Quantennetzwerks (QN) zu demonstrieren. Wir haben vier PPQFC gebaut um die Emissionswellenlängen von einzelnen 40Ca+-Ionen bei 854 nm und neutralen 87Rb-Atomen bei 780 nm in die verlustarmen Telekombänder zwischen 1260 nm und 1625 nm umzuwandeln. Im Konversionsprozess muss die Quanteninformation, kodiert in der Polarisation der Photonen, erhalten bleiben. Dazu nutzen wir Differenzfrequenzerzeugung in Kantenwellenleitern, welche in Polarisationsinterferometer in Form von Sagnac- oder Mach-Zehnder-Aufbauten integriert werden. Für die Konversion einzelner und verschränkter Photonen erreichten wir externe Geräteeffizienzen zwischen 26.5 % und 57.4 %, geringe Hintergrundbeiträge, die Signal-zu-Hintergrund-Verhältnisse über 20 ermöglichen, sowie Prozess-Fidelities > 99.5 %. Mit Hilfe der Konverter konnten wir eine Reihe von Kernelementen von langreichweitigen QNn zeigen: Photonen-Photonen-Verschränkung über 40 km Faser mittels 2-Schritt QFC mit einer Fidelity von 98.9 %, Ion-Telekom-Photon-Verschränkung mit hohen Fidelities bis zu 97.8 %, einen Atom-zu-Telekom-Photon Zustandstransfer, und die Verteilung von Atom-Photon-Verschränkung über 20 km Faser mit einer Fidelity von 78.9 %. Diese Resultate sind vielversprechend um kleine QN mit ≥ 2 Knoten auf die Längenskala einer Stadt auszuweiten

CAPTURE AND ANALYSIS OF SENSOR DATA FOR ASTHMA PATIENTS

Worldwide more than 230 million people suffer from asthma. Reliable and timely guidance for indi-viduals to minimize their risk for asthma attacks is not available. This is largely due to the fact that asthma symptoms are often caused by multiple environmental and personal factors. Many of them are neither captured nor systematically analysed. This is addressed by the project ActOnAir. It aims at a comprehensive capture of health factors and the environmental exposure of individuals, as well as a subsequent analysis in real-time. For this purpose the ActOnAir system provides a mobile sensor box for data collection, a sensor data integration and processing platform, a data mining component and a smartphone application for patients. This contribution outlines the design objectives of the ActOnAir system and discusses corresponding key requirements. The related system architecture is introduced and first results from a prototype implementation are sketched

27 W 2.1 µm OPCPA system for coherent soft X-ray generation operating at 10 kHz

© 2020 Optical Society of America. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for non-commercial purposes and appropriate attribution is maintained. All other rights are reserved.We developed a high power optical parametric chirped-pulse amplification (OPCPA) system at 2.1 µm harnessing a 500 W Yb:YAG thin disk laser as the only pump and signal generation source. The OPCPA system operates at 10 kHz with a single pulse energy of up to 2.7 mJ and pulse duration of 30 fs. The maximum average output power of 27 W sets a new record for an OPCPA system in the 2 µm wavelength region. The soft X-ray continuum generated through high harmonic generation with this driver laser can extend to around 0.55 keV, thus covering the entire water window (284 eV - 543 eV). With a repetition rate still enabling pump-probe experiments on solid samples, the system can be used for many applications.EC/H2020/654148/EU/The Integrated Initiative of European Laser Research Infrastructures/LASERLAB-EUROP

Telecom quantum photonic interface for a 40Ca+ single-ion quantum memory

Entanglement-based quantum networks require quantum photonic interfaces between stationary quantum memories and photons, enabling entanglement distribution. Here we present such a photonic interface, designed for connecting a 40Ca+ singleion quantum memory to the telecom C-band. The interface combines a memory-resonant, cavity-enhanced spontaneous parametric down-conversion photon pair source with bi-directional polarization-conserving quantum frequency conversion. We demonstrate preservation of high-fidelity entanglement during conversion, fiber transmission over up to 40 km and backconversion to the memory wavelength. Even for the longest distance and bi-directional conversion the entanglement fidelity remains larger than 95% (98%) without (with) background correction