63 research outputs found
Optimized Current Density Reconstruction from Widefield Quantum Diamond Magnetic Field Maps
Quantum Diamond Microscopy using Nitrogen-Vacancy (NV) defects in diamond
crystals has enabled the magnetic field imaging of a wide variety of nanoscale
current profiles. Intimately linked with the imaging process is the problem of
reconstructing the current density, which provides critical insight into the
structure under study. This manifests as a non-trivial inverse problem of
current reconstruction from noisy data, typically conducted via Fourier-based
approaches. Learning algorithms and Bayesian methods have been proposed as
novel alternatives for inference-based reconstructions. We study the
applicability of Fourier-based and Bayesian methods for reconstructing
two-dimensional current density maps from magnetic field images obtained from
NV imaging. We discuss extensive numerical simulations to elucidate the
performance of the reconstruction algorithms in various parameter regimes, and
further validate our analysis via performing reconstructions on experimental
data. Finally, we examine parameter regimes that favor specific reconstruction
algorithms and provide an empirical approach for selecting regularization in
Bayesian methods.Comment: 12 Pages main paper with 7 Figures. 6 pages and 2 figures in
supplementary materia
Temperature Dependent Photophysics of Single NV Centers in Diamond
We present a comprehensive study of the temperature and magnetic-field
dependent photoluminescence (PL) of individual NV centers in diamond, spanning
the temperature-range from cryogenic to ambient conditions. We directly observe
the emergence of the NV's room-temperature effective excited state structure
and provide a clear explanation for a previously poorly understood broad
quenching of NV PL at intermediate temperatures around 50 K. We develop a model
that quantitatively explains all of our findings, including the strong impact
that strain has on the temperaturedependence of the NV's PL. These results
complete our understanding of orbital averaging in the NV excited state and
have significant implications for the fundamental understanding of the NV
center and its applications in quantum sensing.Comment: 5 pages, 4 figures plus Supplementary Material. Questions and
comments are welcome. arXiv admin note: text overlap with arXiv:2105.0807
Achieving Zero Stress in Iridium, Chromium, and Nickel Thin Films
We examine a method for achieving zero intrinsic stress in thin films of iridium, chromium, and nickel deposited by magnetron sputter deposition. The examination of the stress in these materials is motivated by efforts to advance the optical performance of light-weight x-ray space telescopes into the regime of sub-arc second resolution that rely on control of the film stress to values within 10-100 MPa. A characteristic feature of the intrinsic stress behavior in chromium and nickel is their sensitivity to the magnitude and sign of the intrinsic stress with argon gas pressure, including the existence of a critical pressure that results in zero film stress. This critical pressure scales linearly with the film's density. While the effect of stress reversal with argon pressure has been previously reported by Hoffman and others for nickel and chromium, we have discovered a similar behavior for iridium. Additionally, we have identified zero stress in iridium shortly after island coalescence. This feature of film growth is used for achieving a total internal stress of -2.89 MPa for a 15.8 nm thick iridium film. The surface roughness of this low-stress film was examined using scanning probe microscopy (SPM) and x-ray reflectivity (XRR) at CuK and these results presented and discussed
Full-Shell X-Ray Optics Development at NASA Marshall Space Flight Center
NASAs Marshall Space Flight Center (MSFC) maintains an active research program toward the development of high-resolution, lightweight, grazing-incidence x-ray optics to serve the needs of future x-ray astronomy missions such as Lynx. MSFC development efforts include both direct fabrication (diamond turning and deterministic computer-controlled polishing) of mirror shells and replication of mirror shells (from figured, polished mandrels). Both techniques produce full-circumference monolithic (primary + secondary) shells that share the advantages of inherent stability, ease of assembly, and low production cost. However, to achieve high-angular resolution, MSFC is exploring significant technology advances needed to control sources of figure error including fabrication- and coating-induced stresses and mounting-induced distortions
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A Common Glaucoma-risk Variant of SIX6 Alters Retinal Nerve Fiber Layer and Optic Disc Measures in a European Population: The EPIC-Norfolk Eye Study.
PURPOSE: A common missense variant in the SIX6 gene (rs33912345) is strongly associated with primary open-angle glaucoma (POAG). We aimed to examine the association of rs33912345 with optic disc and retinal nerve fiber layer (RNFL) measures in a European population. METHODS: We examined participants of the population-based EPIC-Norfolk Eye Study. Participants underwent confocal laser scanning tomography (Heidelberg Retina Tomograph II, HRT) to estimate optic disc rim area and vertical cup-disc ratio (VCDR). Scanning laser polarimetry (GDxVCC) was used to estimate average RNFL thickness. The mean of right and left eye values was considered for each participant. Genotyping was performed using the Affymetrix UK Biobank Axiom Array. Multivariable linear regression with the optic nerve head parameter as outcome variable and dosage of rs33912345 genotype as primary explanatory variable was used, adjusted for age, sex, disc area, axial length, and intraocular pressure. We further repeated analyses stratified into age tertiles. RESULTS: In total, 5433 participants with HRT data and 3699 participants with GDxVCC data were included. Each "C" allele of rs33912345 was associated with a smaller rim area (-0.030 mm [95% CI -0.040, -0.020]; P=5.4×10), a larger VCDR (0.025 [95% CI 0.017, 0.033]; P=3.3×10) and a thinner RNFL (-0.39 μm [95% CI -0.62, -0.15]; P=0.001). The RNFL association was strongest in the oldest age tertile, whereas rim area and VCDR associations were strongest in the youngest and oldest age tertiles. CONCLUSIONS: The protein-coding SIX6 variant rs33912345, previously associated with POAG, has a functional effect on glaucoma-associated optic nerve head traits in Europeans.EPIC-Norfolk infrastructure and core functions are supported by grants from the Medical Research Council (G1000143) and Cancer Research UK (C864/A14136). The clinic for the third health examination was funded by Research into Ageing (262). Genotyping was funded by the Medical
Research Council (MC_PC_13048). Mr Khawaja is supported by a Moorfields Eye Charity grant. Miss Chan is a joint Medical Research Council/Royal College of Ophthalmologists Research Fellow, and received additional support from the International Glaucoma Association. Professor Foster has
received additional support from the Richard Desmond Charitable Trust (via Fight for Sight) and the Department for Health through the award made by the National Institute for Health Research to Moorfields Eye Hospital and the UCL Institute of Ophthalmology for a specialist Biomedical Research Centre for Ophthalmology
Multi-species optically addressable spin defects in a van der Waals material
Optically addressable spin defects hosted in two-dimensional van der Waals
materials represent a new frontier for quantum technologies, promising to lead
to a new class of ultrathin quantum sensors and simulators. Recently, hexagonal
boron nitride (hBN) has been shown to host several types of optically
addressable spin defects, thus offering a unique opportunity to simultaneously
address and utilise various spin species in a single material. Here we
demonstrate an interplay between two separate spin species within a single hBN
crystal, namely boron vacancy defects and visible emitter spins. We
unambiguously prove that the visible emitters are spins and
further demonstrate room temperature coherent control and optical readout of
both spin species. Importantly, by tuning the two spin species into resonance
with each other, we observe cross-relaxation indicating strong inter-species
dipolar coupling. We then demonstrate magnetic imaging using the
defects, both under ambient and cryogenic conditions, and
leverage their lack of intrinsic quantization axis to determine the anisotropic
magnetic susceptibility of a test sample. Our results establish hBN as a
versatile platform for quantum technologies in a van der Waals host at room
temperature
Nanoscale magnetism and magnetic phase transitions in atomically thin CrSBr
Since their first observation in 2017, atomically thin van der Waals (vdW)
magnets have attracted significant fundamental, and application-driven
attention. However, their low ordering temperatures, , sensitivity to
atmospheric conditions and difficulties in preparing clean large-area samples
still present major limitations to further progress. The remarkably stable
high- vdW magnet CrSBr has the potential to overcome these key
shortcomings, but its nanoscale properties and rich magnetic phase diagram
remain poorly understood. Here we use single spin magnetometry to
quantitatively characterise saturation magnetization, magnetic anisotropy
constants, and magnetic phase transitions in few-layer CrSBr by direct magnetic
imaging. We show pristine magnetic phases, devoid of defects on micron
length-scales, and demonstrate remarkable air-stability down the monolayer
limit. We address the spin-flip transition in bilayer CrSBr by direct imaging
of the emerging antiferromagnetic (AFM) to ferromagnetic (FM) phase wall and
elucidate the magnetic properties of CrSBr around its ordering temperature. Our
work will enable the engineering of exotic electronic and magnetic phases in
CrSBr and the realisation of novel nanomagnetic devices based on this highly
promising vdW magnet.Comment: 8 pages, 4 figures, plus supplementary material. Questions and
comments are welcom
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