| 1. |
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- 2019
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Kjaergaard, M., et al.
(författare)
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Demonstration of Density Matrix Exponentiation Using a Superconducting Quantum Processor
- 2022
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Ingår i: Physical Review X. - 2160-3308. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Quantum computers hold the potential to outperform classical supercomputers at certain tasks. To implement algorithms on a quantum computer, programmers use conventional computers and hardware to create a set of classical control signals that implement a desired quantum algorithm. However, feeding the quantum information forward requires an inefficient conversion: extraction of quantum information, conversion to classical control signals, and reinjection of those signals into the system to implement quantum operations. Here, we demonstrate a more natively quantum strategy to programming quantum computers. Our approach uses the density matrix exponentiation (DME) protocol, a general technique for using a quantum state to enact a quantum operation. It can be thought of as a subroutine with which programmers can turn multiple copies of a quantum state into instructions for next steps in a quantum algorithm.We implement DME using two qubits in a superconducting quantum processor. Our implementation relies on a high-fidelity two-qubit gate and a novel technique called quantum measurement emulation to approximately reset a known quantum state. These developments enable us to demonstrate the DME protocol for the first time on a small-scale quantum processor and benchmark its performance.While DME was originally proposed in the context of a specific quantum machine-learning algorithm, it may also represent a fundamentally different approach to quantum programming. It allows the possibility of encoding quantum algorithms directly into quantum states and executing those algorithms on other quantum states, enabling a new class of efficient quantum algorithms.
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| 3. |
- Carvalho, E. de, et al.
(författare)
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EU FP7 INFSO-ICT-317669 METIS, D3.1 Positioning of multi-node/multi-antenna technologies
- 2013
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This document describes the research activity in multi-node/multi-antenna technologies within METIS and positions it with respect to the state-of-the-art in the academic literature and in the standardization bodies. Based on the state-of-the-art and as well as on the METIS objectives,we set the research objectives and we group the different activities (or technology components) into research clusters with similar research objectives. The technologycomponents and the research objectives have been set to achieve an ambidextrous purpose. On one side we aim at providing the METIS system with those technological components that are a natural but non-trivial evolution of 4G. On the other side, we aim at seeking for disruptivetechnologies that could radically change 5G with respect to 4G. Moreover, we mapped the different technology components to METIS’ other activities and to the overall goals of theproject.
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| 4. |
- Fantini, R, et al.
(författare)
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EU FP7 INFSO-ICT-317669 METIS, D3.2 First performance results for multi-node/multi-antenna transmission technologies
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This deliverable describes the current results of the multi-node/multi-antenna technologies investigated within METIS and analyses the interactions within and outside Work Package 3. Furthermore, it identifies the most promising technologies based on the current state of obtained results. This document provides a brief overview of the results in its first part. The second part, namely the Appendix, further details the results, describes the simulation alignment efforts conducted in the Work Package and the interaction of the Test Cases. The results described here show that the investigations conducted in Work Package 3 are maturing resulting in valuable innovative solutions for future 5G systems.
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| 5. |
- Hashemi, Seyed Ehsan, 1986, et al.
(författare)
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Triggering of guiding and antiguiding effects in GaN-based VCSELs
- 2014
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 9001
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Konferensbidrag (refereegranskat)abstract
- We show numerically that many recently proposed GaN-based VCSEL cavities, with DBR mirrors deposited onto the current aperture, balance dangerously close to the border between the guided and antiguided regime. A guided cavity is often preferred because of its lower optical loss, but a strongly antiguided cavity offers built-in modal discrimination favoring single fundamental mode operation. We show that very small changes in the VCSEL structure are sufficient to strongly change the guiding character of the VCSEL cavity, and that thermal lensing caused by device self-heating under operation can dramatically reduce the optical loss but not the modal discrimination in the antiguided cavities.
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| 6. |
- Hustad, J.E., et al.
(författare)
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Reactivity measurements of coke particles in five different flow reactors
- 1990
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Ingår i: Rivista dei Combustibili. - 0370-5463. ; 44:10, s. 257-267
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Experiments on reactivity of 128 μm coke particles in the gas temperature range from 1150 K to 1370 K have been performed in five different flow reactors in the Nordic countries and all the results were calculated by the shrinking particle model. The activation energy is found to be 25 kcal/mol indicating combustion control by the combined effects of chemical kinetic and pore diffusion (zone II combustion). The overall apparent reaction order was found to be 1.0
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| 7. |
- Blücher, D. Bengtsson, et al.
(författare)
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Scanning kelvin probe force microscopy - A useful tool for studying atmospheric corrosion of MgAl alloys in situ
- 2004
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Ingår i: JOURNAL OF THE ELECTROCHEMICAL SOCIETY. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 151:12, s. B621-B626
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Tidskriftsartikel (refereegranskat)abstract
- Scanning Kelvin probe force microscopy (SKPFM) is used to study the initial stages of atmospheric corrosion of an AlMg alloy and of physical vapor deposition (PVD) deposited 2 μm Al dots on pure Mg. The latter system is used as a model of a two-phase AlMg alloy. The influence of CO2 was studied in situ in humid air using SKPFM. This method allows for the in situ investigation of the evolution of the Volta potential during exposure, the resolution being in the submicrometer range. The temperature was 22.0°C, and the relative humidity was 85 or 95%. The concentration of CO2 was <1 or 350 ppm. The corrosion products were analyzed by gravimetry, ion chromatography, X-ray diffraction, scanning electron microscopy, scanning Kelvin probe, and Auger electron spectroscopy. We found that the initial stages of atmospheric corrosion on magnesium are influenced by the presence of cathodic PVD-deposited aluminum. A similar effect was seen in the case of AZ91D, the aluminum-rich β-phase forming the cathodic areas. The β-phase is nobler compared to the substrate because of the higher Al content. In the absence of CO2, the corrosion attack is localized in nature whereas the presence of ambient levels of CO2 results in a more general corrosion attack. The inhibitive effect of CO2 on the atmospheric corrosion of AZ91D is explained by the formation of a passivating layer of Mg5(CO3)4(OH)2⋅5H2O. In the absence of CO2, the increase in pH originating from the cathodic reaction results in the dissolution of aluminum in the passive layer. A corrosion mechanism is proposed explaining the behavior in the two environments.
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| 8. |
- Haglund, Åsa, 1976, et al.
(författare)
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Progress and challenges in electrically pumped GaN-based VCSELs
- 2016
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 9892
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Konferensbidrag (refereegranskat)abstract
- The Vertical-Cavity Surface-Emitting Laser (VCSEL) is an established optical source in short-distance optical communication links, computer mice and tailored infrared power heating systems. Its low power consumption, easy integration into two-dimensional arrays, and low-cost manufacturing also make this type of semiconductor laser suitable for application in areas such as high-resolution printing, medical applications, and general lighting. However, these applications require emission wavelengths in the blue-UV instead of the established infrared regime, which can be achieved by using GaN-based instead of GaAs-based materials. The development of GaN-based VCSELs is challenging, but during recent years several groups have managed to demonstrate electrically pumped GaN-based VCSELs with close to 1 mW of optical output power and threshold current densities between 3-16 kA/cm2. The performance is limited by challenges such as achieving high-reflectivity mirrors, vertical and lateral carrier confinement, efficient lateral current spreading, accurate cavity length control and lateral optical mode confinement. This paper summarizes different strategies to solve these issues in electrically pumped GaN-VCSELs together with state-of-the-art results. We will highlight our work on combined transverse current and optical mode confinement, where we show that many structures used for current confinement result in unintentionally optically anti-guided resonators. Such resonators can have a very high optical loss, which easily doubles the threshold gain for lasing. We will also present an alternative to the use of distributed Bragg reflectors as high-reflectivity mirrors, namely TiO2/air high contrast gratings (HCGs). Fabricated HCGs of this type show a high reflectivity (>95%) over a 25 nm wavelength span.
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| 9. |
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| 10. |
- Nilsson, R. Henrik, 1976, et al.
(författare)
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A comprehensive, automatically updated fungal ITS sequence dataset for reference-based chimera control in environmental sequencing efforts
- 2015
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Ingår i: Microbes and Environments. - 1342-6311 .- 1347-4405. ; 30:2, s. 145-150
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Tidskriftsartikel (refereegranskat)abstract
- The nuclear ribosomal internal transcribed spacer (ITS) region is the most commonly chosen genetic marker for the molecular identification of fungi in environmental sequencing and molecular ecology studies. Several analytical issues complicate such efforts, one of which is the formation of chimeric—artificially joined—DNA sequences during PCR amplification or sequence assembly. Several software tools are currently available for chimera detection, but rely to various degrees on the presence of a chimera-free reference dataset for optimal performance. However, no such dataset is available for use with the fungal ITS region. This study introduces a comprehensive, automatically updated reference dataset for fungal ITS sequences based on the UNITE database for the molecular identification of fungi. This dataset supports chimera detection throughout the fungal kingdom and for full-length ITS sequences as well as partial (ITS1 or ITS2 only) datasets. The performance of the dataset on a large set of artificial chimeras was above 99.5%, and we subsequently used the dataset to remove nearly 1,000 compromised fungal ITS sequences from public circulation. The dataset is available at http://unite.ut.ee/repository.php and is subject to web-based third-party curation.
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