| 1. |
- McMichael, C. N. H., et al.
(författare)
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30,000 years of landscape and vegetation dynamics in a mid-elevation Andean valley
- 2021
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Ingår i: Quaternary Science Reviews. - : Elsevier. - 0277-3791 .- 1873-457X. ; 258
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Tidskriftsartikel (refereegranskat)abstract
- The mid-elevation settings of the Andes are important biodiversity hotspots, yet little is known of their long-term ecology or environmental change. Here, we assess 30,000 years of landscape and vegetation dynamics on an alluvial terrace located in a mid-elevation valley of the Ecuadorian Andes (Campo Libre). We used loss-on-ignition and particle size analysis to reconstruct past river dynamics, charcoal analysis to reconstruct past fire regimes, and phytolith analysis to reconstruct vegetation change through time. Our results show that Campo Libre was a part of the active floodplain system of the Quijos River until 18,000 cal yr BP. The biggest vegetation change in vegetation at Campo Libre occurred ca. 13,000 cal yr BP, when the site warmed and dried, transforming the swampy alluvial terrace into a palm forest. As Ho-locene precipitation increased, the site transformed back into a swamp around 7500 cal yr BP, and it remained that way until maize agriculture began around 4600 cal yr BP. Local and regional fires were absent from the system until regional fires were detected ca. 3300 cal yr BP. By ca. 2700 cal yr BP, maize cultivation became frequent and regular. Climate, tectonic activity, and the human history have shaped the modern vegetation around Campo Libre, although during different periods of the Holocene. Our results demonstrate the ability of phytoliths to reconstruct vegetation change through time, and show that the mid-elevation Andean valley systems were highly dynamic over the last 30,000 years.
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| 2. |
- Bosma, Tom, et al.
(författare)
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Identification and tunable optical coherent control of transition-metal spins in silicon carbide
- 2018
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Ingår i: NPJ QUANTUM INFORMATION. - : SPRINGERNATURE. - 2056-6387. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- Color centers in wide-bandgap semiconductors are attractive systems for quantum technologies since they can combine long-coherent electronic spin and bright optical properties. Several suitable centers have been identified, most famously the nitrogen-vacancy defect in diamond. However, integration in communication technology is hindered by the fact that their optical transitions lie outside telecom wavelength bands. Several transition-metal impurities in silicon carbide do emit at and near telecom wavelengths, but knowledge about their spin and optical properties is incomplete. We present all-optical identification and coherent control of molybdenum-impurity spins in silicon carbide with transitions at near-infrared wavelengths. Our results identify spin S= 1/2 for both the electronic ground and excited state, with highly anisotropic spin properties that we apply for implementing optical control of ground-state spin coherence. Our results show optical lifetimes of similar to 60 ns and inhomogeneous spin dephasing times of similar to 0.3 mu S, establishing relevance for quantum spin-photon interfacing.
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| 3. |
- Labrador-Páez, Lucia, et al.
(författare)
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pH dependence of water anomaly temperature investigated by Eu(III) cryptate luminescence
- 2020
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Ingår i: Analytical and Bioanalytical Chemistry. - : Springer Science and Business Media LLC. - 1618-2642 .- 1618-2650. ; 412:1, s. 73-80
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Tidskriftsartikel (refereegranskat)abstract
- Although water has been extensively studied, not all of its unique properties have been fully understood. There is still controversy about the temperature at which hydrogen bonds are broken or weakened, producing the anomalous temperature dependence of many water properties. Different temperatures between 23 and 48 °C have been reported, but no study has scrutinized the reasons for this discrepancy. We suggest the determining role of pH in the alteration of the water anomaly temperature. We employed a luminescent europium trisbipyridine cryptate, which is highly sensitive to changes in the arrangement of water molecules and whose luminescence intensity and lifetime are not significantly influenced by variations over a broad pH range. Our results revealed an increase of the crossover temperature from circa 35 °C at pH 3.5 to circa 45 °C at pH 7 to 9, which explains the discrepancies of previous studies. The pH dependence of water anomaly temperature is an important property for a better understanding of water and water-based systems and applications.
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| 4. |
- Zwier, Olger V, et al.
(författare)
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Electromagnetically induced transparency in inhomogeneously broadened divacancy defect ensembles in SiC
- 2022
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 131:9
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Tidskriftsartikel (refereegranskat)abstract
- Electromagnetically induced transparency (EIT) is a phenomenon that can provide strong and robust interfacing between optical signals and quantum coherence of electronic spins. In its archetypical form, mainly explored with atomic media, it uses a (near-)homogeneous ensemble of three-level systems, in which two low-energy spin-1/2 levels are coupled to a common optically excited state. We investigate the implementation of EIT with c-axis divacancy color centers in silicon carbide. While this material has attractive properties for quantum device technologies with near-IR optics, implementing EIT is complicated by the inhomogeneous broadening of the optical transitions throughout the ensemble and the presence of multiple ground-state levels. These may lead to darkening of the ensemble upon resonant optical excitation. Here, we show that EIT can be established with high visibility also in this material platform upon careful design of the measurement geometry. Comparison of our experimental results with a model based on the Lindblad equations indicates that we can create coherences between different sets of two levels all-optically in these systems, with potential impact for RF-free quantum sensing applications. Our work provides an understanding of EIT in multi-level systems with significant inhomogeneities, and our considerations are valid for a wide array of defects in semiconductors. Published under an exclusive license by AIP Publishing.
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