Semiconductor quantum dots for photonic quantum repeaters

Current information exchange is based on optical fibers and satellite communication via free-space links, where security is provided by mathematical complexity. However, it could potentially be threatened by paradigm shifts in computing technology. Encryption techniques using quantum key distribution based on entangled photons would allow for theoretical full secure communication. The very same platform, entangled photons, can also be employed as a core element to establish multi-node secure communication—a concept known as quantum network. For these reasons, en tangled photon sources might be the core of future quantum networks for secure communication. In this thesis, I study GaAs/AlGaAs quantum dots as entangled photon sources. After giving a general overview on the fundamentals of photonic quantum networks and GaAs droplet-etched quantum dots, I mainly focus on two aspects of the development of this technology. First, limits of the source performance as entangled photon sources and second, applications of entangled photons from quantum dots for secure communication. The prior includes degrading effects of entanglement in these quantum dots, especially based on multiphoton emission and optical Stark effect induced by the particular entangled-photon generation technique, resonant two-photon excitation. The experimental results demonstrate that multiphoton emission is negligible under practical conditions, which is supported by a probabilistic model. The finite excitation laser pulse duration in resonant two-photon excitation, on the other hand, induces an optical Stark effect. The measurements in this thesis support the theoretical predictions and an entanglement reduction by increasing excitation laser pulse length is observed experimentally. If some conditions are met, GaAs/AlGaAs quantum dots emit highly entangled photons, which are utilized in the second part of this thesis by applying them in entanglement-based quantum key distribution protocols. The demonstrations range from the first implementation of quantum dots as entangled photon sources for secure communication in fiber and free-space, to a continuous secret key exchange over three days. The second test case, in particular, tackles the challenges of real-life applications such as sunlight and mild rain. At the end, I provide a brief outlook on how to use entangled photons from GaAs/AlGaAs quantum dots to transfer information from one node of a network, namely a quantum repeater, to another by proposing an experiment called remote quantum teleportation

Flood risk – Prevention and Impact on Agricultural Lands

Recent extreme weather events have resulted in an ongoing discussion on the issues of land use and compensation payments within Austrian agriculture. Building on a functional evaluation system for agricultural lands as developed within the Interreg IIIB project “ILUP”, the national project “Agriculture and Flooding” has as its goal to classify the flood-protection contribution and flood sensitivity of agricultural lands. This, in turn, enables the recommendation of targeted measures for potentially improving flood situations, as well as an estimate of their implementation costs. In addition to the digital soil map, other fundamental sources used for the project are the digital flood risk map, IACS land-use data and works by the Institute for Land and Water Management Research. Reference values and marginal returns sourced from the Federal Institute of Agricultural Economics also flow into the cost estimates for the recommended combination. The results will contribute to an understanding of the multifunctionality of agricultural lands and to the setting of priorities on a regional scale regarding packaged flood-prevention and damage-minimization. However, the results at hand can only serve as one step toward regional flood protection projects, whose development will require the cooperation of all interest groups.Agriculture, Multifunctionality, Sustainability, Flood Risk, Resource /Energy Economics and Policy, Q24, Q25, Q54, Q56,

Signatures of the Optical Stark Effect on Entangled Photon Pairs from Resonantly-Pumped Quantum Dots

Two-photon resonant excitation of the biexciton-exciton cascade in a quantum dot generates highly polarization-entangled photon pairs in a near-deterministic way. However, there are still open questions on the ultimate level of achievable entanglement. Here, we observe the impact of the laser-induced AC-Stark effect on the spectral emission features and on entanglement. A shorter emission time, longer laser pulse duration, and higher pump power all result in lower values of concurrence. Nonetheless, additional contributions are still required to fully account for the observed below-unity concurrence.Comment: 7 pages, 3 figure

A source of entangled photons based on a cavity-enhanced and strain-tuned GaAs quantum dot

A quantum-light source that delivers photons with a high brightness and a high degree of entanglement is fundamental for the development of efficient entanglement-based quantum-key distribution systems. Among all possible candidates, epitaxial quantum dots are currently emerging as one of the brightest sources of highly entangled photons. However, the optimization of both brightness and entanglement currently requires different technologies that are difficult to combine in a scalable manner. In this work, we overcome this challenge by developing a novel device consisting of a quantum dot embedded in a circular Bragg resonator, in turn, integrated onto a micromachined piezoelectric actuator. The resonator engineers the light-matter interaction to empower extraction efficiencies up to 0.69(4). Simultaneously, the actuator manipulates strain fields that tune the quantum dot for the generation of entangled photons with fidelities up to 0.96(1). This hybrid technology has the potential to overcome the limitations of the key rates that plague current approaches to entanglement-based quantum key distribution and entanglement-based quantum networks. Introductio

A multipair-free source of entangled photons in the solid state

Unwanted multiphoton emission commonly reduces the degree of entanglement of photons generated by non-classical light sources and, in turn, hampers their exploitation in quantum information science and technology. Quantum emitters have the potential to overcome this hurdle but, so far, the effect of multiphoton emission on the quality of entanglement has never been addressed in detail. Here, we tackle this challenge using photon pairs from a resonantly-driven quantum dot and comparing quantum state tomography and second-order coherence measurements as a function of the excitation power. We observe that the relative (absolute) multiphoton emission probability is as low as $p_m= (5.6 \pm 0.6)10^{-4}$ ($p_2= (1.5 \pm 0.3)10^{-6}$) at the maximum source brightness, values that lead to a negligible effect on the degree of entanglement. In stark contrast with probabilistic sources of entangled photons, we also demonstrate that the multiphoton emission probability and the degree of entanglement remain practically unchanged against the excitation power for multiple Rabi cycles, despite we clearly observe oscillations in the second-order coherence measurements. Our results, explained by a theoretical model that we develop to estimate the actual multiphoton contribution in the two-photon density matrix, highlight that quantum dots can be regarded as a multipair-free source of entangled photons in the solid state

Long-term efficacy and safety of nusinersen in adults with 5q spinal muscular atrophy: a prospective European multinational observational study

Background Evidence for the efficacy of nusinersen in adults with 5q-associated spinal muscular atrophy (SMA) has been demonstrated up to a period of 16 months in relatively large cohorts but whereas patients reach a plateau over time is still to be demonstrated. We investigated the efficacy and safety of nusinersen in adults with SMA over 38 months, the longest time period to date in a large cohort of patients from multiple clinical sites. Methods Our prospective, observational study included adult patients with SMA from Germany, Switzerland, and Austria (July 2017 to May 2022). All participants had genetically-confirmed, 5q-associated SMA and were treated with nusinersen according to the label. The total Hammersmith Functional Motor Scale Expanded (HFMSE) and Revised Upper Limb Module (RULM) scores, and 6-min walk test (6 MWT; metres), were recorded at baseline and 14, 26, and 38 months after treatment initiation, and pre and post values were compared. Adverse events were also recorded. Findings Overall, 389 patients were screened for eligibility and 237 were included. There were significant increases in all outcome measures compared with baseline, including mean HFMSE scores at 14 months (mean difference 1.72 [95% CI 1.19–2.25]), 26 months (1.20 [95% CI 0.48–1.91]), and 38 months (1.52 [95% CI 0.74–2.30]); mean RULM scores at 14 months (mean difference 0.75 [95% CI 0.43–1.07]), 26 months (mean difference 0.65 [95% CI 0.27–1.03]), and 38 months (mean difference 0.72 [95% CI 0.25–1.18]), and 6 MWT at 14 months (mean difference 30.86 m [95% CI 18.34–43.38]), 26 months (mean difference 29.26 m [95% CI 14.87–43.65]), and 38 months (mean difference 32.20 m [95% CI 10.32–54.09]). No new safety signals were identified. Interpretation Our prospective, observational, long-term (38 months) data provides further real-world evidence for the continuous efficacy and safety of nusinersen in a large proportion of adult patients with SMA. Funding Financial support for the registry from Biogen, Novartis and Roche

Head-down tilt bed rest with or without artificial gravity is not associated with motor unit remodeling

© 2020, The Author(s). Purpose: The objective of this study was to assess whether artificial gravity attenuates any long-duration head-down 60 bed rest (HDBR)-induced alterations in motor unit (MU) properties. Methods: Twenty-four healthy participants (16 men; 8 women; 26–54 years) underwent 60-day HDBR with (n = 16) or without (n = 8) 30 min artificial gravity daily induced by whole-body centrifugation. Compound muscle action potential (CMAP), MU number (MUNIX) and MU size (MUSIX) were estimated using the method of Motor Unit Number Index in the Abductor digiti minimi and tibialis anterior muscles 5 days before (BDC-5), and during day 4 (HDT4) and 59 (HDT59) of HDBR. Results: The CMAP, MUNIX, and MUSIX at baseline did not change significantly in either muscle, irrespective of the intervention (p > 0.05). Across groups, there were no significant differences in any variable during HDBR, compared to BDC-5. Conclusion: Sixty days of HDBR with or without artificial gravity does not induce alterations in motor unit number and size in the ADM or TA muscles in healthy individuals

Improved upper limb function in non-ambulant children with SMA type 2 and 3 during nusinersen treatment: a prospective 3-years SMArtCARE registry study

Background The development and approval of disease modifying treatments have dramatically changed disease progression in patients with spinal muscular atrophy (SMA). Nusinersen was approved in Europe in 2017 for the treatment of SMA patients irrespective of age and disease severity. Most data on therapeutic efficacy are available for the infantile-onset SMA. For patients with SMA type 2 and type 3, there is still a lack of sufficient evidence and long-term experience for nusinersen treatment. Here, we report data from the SMArtCARE registry of non-ambulant children with SMA type 2 and typen 3 under nusinersen treatment with a follow-up period of up to 38 months. Methods SMArtCARE is a disease-specific registry with data on patients with SMA irrespective of age, treatment regime or disease severity. Data are collected during routine patient visits as real-world outcome data. This analysis included all non-ambulant patients with SMA type 2 or 3 below 18 years of age before initiation of treatment. Primary outcomes were changes in motor function evaluated with the Hammersmith Functional Motor Scale Expanded (HFMSE) and the Revised Upper Limb Module (RULM). Results Data from 256 non-ambulant, pediatric patients with SMA were included in the data analysis. Improvements in motor function were more prominent in upper limb: 32.4% of patients experienced clinically meaningful improvements in RULM and 24.6% in HFMSE. 8.6% of patients gained a new motor milestone, whereas no motor milestones were lost. Only 4.3% of patients showed a clinically meaningful worsening in HFMSE and 1.2% in RULM score. Conclusion Our results demonstrate clinically meaningful improvements or stabilization of disease progression in non-ambulant, pediatric patients with SMA under nusinersen treatment. Changes were most evident in upper limb function and were observed continuously over the follow-up period. Our data confirm clinical trial data, while providing longer follow-up, an increased number of treated patients, and a wider range of age and disease severity

Evaluation of Educational Measures of the Austrian Rural Development Programme - Results and Experiences

The Austrian Rural Development Programme of the current period 2000 - 2006 includes the measure "Vocational training" to improve the qualification of persons involved in agriculture and forestry as well as to help them convert their operations to other uses. The educational measures play an important role in the implementation of the whole programme, and the acceptance of the programme rises due to the accompanying education and training measures. Firstly, the measure "Vocational training" is designed to support their participation in training and qualification courses (participant support) and, secondly, it was developed to provide assistance in the preparation, implementation, processing and postprocessing of training and courses (support provided to educational institutions). Between 2000 and 2004, as much as 0.6% of the total funds of the rural development programme was spent on the "vocational training" measure. Total costs of 53.8 million euros were borne by the EU (28%), by the Austrian Federal Government (17%) and by the provincial governments (11%) - while the remaining 44% were contributed by the applicants themselves. 63% of the supported participants were males, but they received only 58% of the subsidies. The majority of participants attended computer - and telecommunication courses, courses in animal production and business management. The participants' were predominantly in the age between 35 and 49 years and nearly all of the participants were farm managers. The evaluation results suggest that the range of beneficiaries should be widened, and that there should be an increased support given to women and young people as well as higher endowments granted for vocational training. Additionally, the results make it clear that high-quality data are absolutely vital to achieve meaningful evaluations