| 1. |
- Niemi, MEK, et al.
(author)
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- 2021
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swepub:Mat__t
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| 2. |
- Christle, David J., et al.
(author)
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Isolated electron spins in silicon carbide with millisecond coherence times
- 2015
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In: Nature Materials. - : Nature Publishing Group. - 1476-1122 .- 1476-4660. ; 14:2, s. 160-163
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Journal article (peer-reviewed)abstract
- The elimination of defects from SiC has facilitated its move to the forefront of the optoelectronics and power-electronics industries(1). Nonetheless, because certain SiC defects have electronic states with sharp optical and spin transitions, they are increasingly recognized as a platform for quantum information and nanoscale sensing(2-16). Here, we show that individual electron spins in high-purity monocrystalline 4H-SiC can be isolated and coherently controlled. Bound to neutral divacancy defects(2,3), these states exhibit exceptionally long ensemble Hahn-echo spin coherence times, exceeding 1 ms. Coherent control of single spins in a material amenable to advanced growth and microfabrication techniques is an exciting route towards wafer-scale quantum technologies.
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| 3. |
- Christle, David J., et al.
(author)
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Isolated Spin Qubits in SiC with a High-Fidelity Infrared Spin-to-Photon Interface
- 2017
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In: Physical Review X. - : AMER PHYSICAL SOC. - 2160-3308. ; 7:2
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Journal article (peer-reviewed)abstract
- The divacancies in SiC are a family of paramagnetic defects that show promise for quantum communication technologies due to their long-lived electron spin coherence and their optical addressability at near-telecom wavelengths. Nonetheless, a high-fidelity spin-photon interface, which is a crucial prerequisite for such technologies, has not yet been demonstrated. Here, we demonstrate that such an interface exists in isolated divacancies in epitaxial films of 3C-SiC and 4H-SiC. Our data show that divacancies in 4H-SiC have minimal undesirable spin mixing, and that the optical linewidths in our current sample are already similar to those of recent remote entanglement demonstrations in other systems. Moreover, we find that 3C-SiC divacancies have a millisecond Hahn-echo spin coherence time, which is among the longest measured in a naturally isotopic solid. The presence of defects with these properties in a commercial semiconductor that can be heteroepitaxially grown as a thin film on Si shows promise for future quantum networks based on SiC defects.
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| 4. |
- de las Casas, Charles F., et al.
(author)
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Stark tuning and electrical charge state control of single divacancies in silicon carbide
- 2017
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In: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 111:26
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Journal article (peer-reviewed)abstract
- Neutrally charged divacancies in silicon carbide (SiC) are paramagnetic color centers whose long coherence times and near-telecom operating wavelengths make them promising for scalable quantum communication technologies compatible with existing fiber optic networks. However, local strain inhomogeneity can randomly perturb their optical transition frequencies, which degrades the indistinguishability of photons emitted from separate defects and hinders their coupling to optical cavities. Here, we show that electric fields can be used to tune the optical transition frequencies of single neutral divacancy defects in 4H-SiC over a range of several GHz via the DC Stark effect. The same technique can also control the charge state of the defect on microsecond timescales, which we use to stabilize unstable or non-neutral divacancies into their neutral charge state. Using fluorescence-based charge state detection, we show that both 975 nm and 1130 nm excitation can prepare their neutral charge state with near unity efficiency. (C) 2017 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons. org/licenses/by/4.0/).
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| 5. |
- Falk, Abram L., et al.
(author)
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Optical Polarization of Nuclear Spins in Silicon Carbide
- 2015
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In: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 114:24, s. 247603-
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Journal article (peer-reviewed)abstract
- We demonstrate optically pumped dynamic nuclear polarization of Si-29 nuclear spins that are strongly coupled to paramagnetic color centers in 4H- and 6H-SiC. The 99% +/- 1% degree of polarization that we observe at room temperature corresponds to an effective nuclear temperature of 5 mu K. By combining ab initio theory with the experimental identification of the color centers optically excited states, we quantitatively model how the polarization derives from hyperfine-mediated level anticrossings. These results lay a foundation for SiC-based quantum memories, nuclear gyroscopes, and hyperpolarized probes for magnetic resonance imaging.
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| 6. |
- Hedman, Kristofer, et al.
(author)
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Impact of the distance from the chest wall to the heart on surface ECG voltage in athletes
- 2020
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In: BMJ OPEN SPORT & EXERCISE MEDICINE. - : BMJ Publishing Group Ltd. - 2055-7647. ; 6:1
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Journal article (peer-reviewed)abstract
- ObjectiveAvailable ECG criteria for detection of left ventricular (LV) hypertrophy have been reported to have limited diagnostic capability. Our goal was to describe how the distance between the chest wall and the left ventricle determined by echocardiography affected the relationship between ECG voltage and LV mass (LVM) in athletes.MethodsWe retrospectively evaluated digitised ECG data from college athletes undergoing routine echocardiography as part of their preparticipation evaluation. Along with LV mass and volume, we determined the chest wall-LV distance in the parasternal short-axis and long-axis views from two-dimensional transthoracic echocardiographic images and explored the relation with ECG QRS voltages in all leads, as well as summed voltages as included in six major ECG-LVH criteria.Results239 athletes (43 women) were included (age 191years). In men, greater LV-chest wall distance was associated with higher R-wave amplitudes in leads aVL and I (R=0.20and R=0.25, both p<0.01), while in women greater distance was associated with higher R-amplitudes in V5 and V6 (R=0.42and R=0.34, both p<0.01). In women, the chest wall-LV distance was the only variable independently (and positively) associated with R V5 voltage, while LVM, height and weight contributed to the relationship in men.ConclusionsThe chest wall-LV distance was weakly associated with ECG voltage in athletes. Inconsistent associations in men and women imply different intrathoracic factors affecting impedance and conductance between sexes. This may help explain the poor relationship between QRS voltage and LVM in athletes.
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| 7. |
- Hedman, Kristofer, 1984-, et al.
(author)
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Limitations of Electrocardiography for Detecting Left Ventricular Hypertrophy or Concentric Remodeling in Athletes
- 2020
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In: American Journal of Medicine. - : Elsevier. - 0002-9343 .- 1555-7162. ; 133:1, s. 123-132.e8
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Journal article (peer-reviewed)abstract
- BackgroundElectrocardiography (ECG) is used to screen for left ventricular hypertrophy (LVH), but common ECG-LVH criteria have been found less effective in athletes. The purpose of this study was to comprehensively evaluate the value of ECG for identifying athletes with LVH or a concentric cardiac phenotype.MethodsA retrospective analysis of 196 male Division I college athletes routinely screened with ECG and echocardiography within the Stanford Athletic Cardiovascular Screening Program was performed. Left-ventricular mass and volume were determined using echocardiography. LVH was defined as left ventricular mass (LVM) > 102 g/m²; a concentric cardiac phenotype as LVM-to-volume (M/V) ≥ 1.05 g/mL. Twelve-lead electrocardiograms including high-resolution time intervals and QRS voltages were obtained. Thirty-seven previously published ECG-LVH criteria were applied, of which the majority have never been evaluated in athletes. C-statistics, including area under the receiver operating curve (AUC) and likelihood ratios were calculated.ResultsECG lead voltages were poorly associated with LVM (r = 0.18-0.30) and M/V (r = 0.15-0.25). The proportion of athletes with ECG-LVH was 0%-74% across criteria, with sensitivity and specificity ranging between 0% and 91% and 27% and 99.5%, respectively. The average AUC of the criteria in identifying the 11 athletes with LVH was 0.57 (95% confidence interval [CI] 0.56-0.59), and the average AUC for identifying the 8 athletes with a concentric phenotype was 0.59 (95% CI 0.56-0.62).ConclusionThe diagnostic capacity of all ECG-LVH criteria were inadequate and, therefore, not clinically useful in screening for LVH or a concentric phenotype in athletes. This is probably due to the weak association between LVM and ECG voltage.
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| 8. |
- Ivády, Viktor, et al.
(author)
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High-Fidelity Bidirectional Nuclear Qubit Initialization in SiC
- 2016
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In: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 117:22
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Journal article (peer-reviewed)abstract
- Dynamic nuclear polarization (DNP) is an attractive method for initializing nuclear spins that are strongly coupled to optically active electron spins because it functions at room temperature and does not require strong magnetic fields. In this Letter, we theoretically demonstrate that DNP, with near-unity polarization efficiency, can be generally realized in weakly coupled electron spin-nuclear spin systems. Furthermore, we theoretically and experimentally show that the nuclear spin polarization can be reversed by magnetic field variations as small as 0.8 Gauss. This mechanism offers new avenues for DNP-based sensors and radio-frequency free control of nuclear qubits.
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| 9. |
- Ivády, Viktor, et al.
(author)
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Theoretical model of dynamic spin polarization of nuclei coupled to paramagnetic point defects in diamond and silicon carbide
- 2015
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In: Physical Review B. Condensed Matter and Materials Physics. - : AMER PHYSICAL SOC. - 1098-0121 .- 1550-235X. ; 92:11, s. 115206-
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Journal article (peer-reviewed)abstract
- Dynamic nuclear spin polarization (DNP) mediated by paramagnetic point defects in semiconductors is a key resource for both initializing nuclear quantum memories and producing nuclear hyperpolarization. DNP is therefore an important process in the field of quantum-information processing, sensitivity-enhanced nuclear magnetic resonance, and nuclear-spin-based spintronics. DNP based on optical pumping of point defects has been demonstrated by using the electron spin of nitrogen-vacancy (NV) center in diamond, and more recently, by using divacancy and related defect spins in hexagonal silicon carbide (SiC). Here, we describe a general model for these optical DNP processes that allows the effects of many microscopic processes to be integrated. Applying this theory, we gain a deeper insight into dynamic nuclear spin polarization and the physics of diamond and SiC defects. Our results are in good agreement with experimental observations and provide a detailed and unified understanding. In particular, our findings show that the defect electron spin coherence times and excited state lifetimes are crucial factors in the entire DNP process.
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