Optically active spin defects are promising candidates for solid-state quantum information and sensing applications. To use these defects in quantum applications coherent manipulation of their spin state is required. Here, we realize coherent control of ensembles of boron vacancy centers in hexagonal boron nitride (hBN). Specifically, by applying pulsed spin resonance protocols, we measure a spin-lattice relaxation time of 18 microseconds and a spin coherence time of 2 microseconds at room temperature. The spin-lattice relaxation time increases by three orders of magnitude at cryogenic temperature. By applying a method to decouple the spin state from its inhomogeneous nuclear environment the optically detected magnetic resonance linewidth is substantially reduced to several tens of kilohertz. Our results are important for the employment of van der Waals materials for quantum technologies, specifically in the context of high resolution quantum sensing of two-dimensional heterostructures, nanoscale devices, and emerging atomically thin magnets.
Spin defects in solid-state materials are strong candidate systems for quantum information technology and sensing applications. Here we explore in details the recently discovered negatively charged boron vacancies (VB−) in hexagonal boron nitride (hBN) and demonstrate their use as atomic scale sensors for temperature, magnetic fields and externally applied pressure. These applications are possible due to the high-spin triplet ground state and bright spin-dependent photoluminescence of the VB−. Specifically, we find that the frequency shift in optically detected magnetic resonance measurements is not only sensitive to static magnetic fields, but also to temperature and pressure changes which we relate to crystal lattice parameters. We show that spin-rich hBN films are potentially applicable as intrinsic sensors in heterostructures made of functionalized 2D materials.
Holotomography is an extension of computed tomography where samples with low X-ray absorption can be investigated with higher contrast. In order to achieve this, the imaging system must yield an optical resolution of a few micrometers or less, which reduces the measurement area (field of view = FOV) to a few mm at most. If the sample size, however, exceeds the field of view (called local tomography or region of interest = ROI CT), filter problems arise during the CT reconstruction and phase retrieval in holotomography. In this paper, we will first investigate the practical impact of these filter problems and discuss approximate solutions. Secondly, we will investigate the effectiveness of a technique we call “multiscalar holotomography”, where, in addition to the ROI CT, a lower resolution non-ROI CT measurement is recorded. This is used to avoid the filter problems while simultaneously reconstructing a larger part of the sample, albeit with a lower resolution in the additional area.
Synchrotron phase-contrast micro-tomography is considered the gold standard in non-destructive volumetric imaging of millimeter and centimeter-sized objects. Micro-tomography beamlines are operating at many synchrotron radiation facilities, including the Extremely Brilliant Source (EBS) at the European Synchrotron Radiation Facility (ESRF). Applications favor objects which cannot be sufficiently resolved by state-of-the-art industrial micro-CT scanners. Synchrotron tomography features much superior time resolution, e.g., for in situ micro-CT, as well as superior photon flux, thus making this method suitable for Region of Interest scanning (i.e., multiresolution tomography). This report presents first results from the EBS' latest industrial beamline BM18, which was built for hierarchical propagation phase-contrast tomography. BM18 makes use of the exceptionally high coherence of the new ESRF-EBS lattice. Thanks to the wide polychromatic high-energy beam, one can scan and zoom into larger parts, e.g., from additive manufacturing or battery packs. In particular, BM18 allows for recording multiple scans at different resolutions ranging from 42 μm down to 0.6 μm, without the need to remove the object or manually change detectors. Free space propagation of up to 36 m yields excellent phase-contrast which in turn enhances the resolving power of the system. BM18 is generating an unprecedented amount of very large datasets. Consequently, novel strategies for data processing, storage and visualization are under development for this particular instrument.
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