Experimental and Theoretical Analysis of Noise Strength and Environmental Correlation Time for Ensembles of Nitrogen-Vacancy Centers in Diamond

NV centers in diamond have been considered as an important building block for the realization of quantum information processing such as quantum simulation, quantum memory, and quantum metrology. To maximize the potential of the NV centers, it is essential to understand the mechanism of the decoherence. Existing theories predicted a relationship between the coherence time and spin concentration (a sum of the concentration of the NV center and P1 center) in diamond. However, a systematic experimental study of the spin concentration dependence of the coherence time was still missing. Here, we experimentally and theoretically investigate the Hahn echo decay curve with several diamond samples with different spin concentration. The Hahn echo results show that we observe a non-exponential decay for the low spin concentration while an exponential decay is dominant for the high spin concentration. By fitting the decay curve with a theoretical model, we show that both the amplitude and correlation time of the environmental noise have a clear dependence on the spin concentration. These results are essential to optimize the NV center concentration as high-performance quantum devices, particularly as quantum sensors

Effects of Three Types of Organic Fertilizers on Greenhouse Gas Emissions in a Grassland on Andosol in Southern Hokkaido, Japan

Reduction of chemical fertilizers and effective use of livestock excrement are required for the realization of sustainable agriculture and reduction of greenhouse gas (GHG) emissions. The purpose of this study was to estimate the reduction rate of GHG emissions represented by comparing global warming potential (GWP) using organic fertilizers instead of chemical fertilizers. The study was conducted in a managed grassland on Andosol in southern Hokkaido for 3 years from May 2017 to April 2020. There were five treatment plots: no fertilizer, chemical fertilizer, manure, slurry, and digestive fluid. Organic fertilizers were applied such that the amount of NPK did not exceed the recommended application rate, and the shortage was supplemented with chemical fertilizers. Fluxes in CO2 caused by heterotrophic respiration (RH), CH4, and N2O were measured using the closed chamber method. Net ecosystem carbon balance (NECB) was obtained as net primary production + organic fertilizer application-RH-harvest. The GWP was estimated by CO2 equivalent NECB and CH4 and N2O emissions in each treatment. Chemical fertilizer nitrogen application rates in the organic fertilizer treatments were reduced by 10% for manure, 19.7% for slurry and 29.7% for digestive fluid compared to chemical fertilizer only, but the grass yields were not significantly different among the fertilizer treatments. The 3-year NECB showed significantly smallest carbon loss in manure treatment, and smaller carbon loss in the organic fertilizer treatments than in the chemical fertilizer only. The reduction rate in the GWP with use of organic fertilizers relative to that of chemical fertilizer was 16.5% for slurry, 27.0% for digestive fluid, and 36.2% for manure. The NECB accounted for more than 90% of the GWP in all treatments. CH4 emissions were chemical fertilizer only > digestive fluid > manure. As a conclusion, these organic fertilizers can be used without no reduction of crop yield instead of chemical fertilizer, however, manure is the best way to increase soil carbon and to decrease GWP, followed by digestive fluid