Electron paramagnetic resonance and Hall measurements show consistently the presence of two donors ( D1 and D2) in state-of-the-art, nominally undoped ZnO single crystals. Using electron nuclear double resonance it is found that D1 shows hyperfine interaction with more than 50 shells of surrounding 67Zn nuclei, proving that it is a shallow, effective-mass-like donor. In addition D1 exhibits a single interaction with a H nucleus ( a(H) = 1.4 MHz), thus H is the defining element. It is in agreement with the prediction of Van de Walle [Phys. Rev. Lett. 85, 1012 (2000)] that H acts as a donor in ZnO. The concentration of D1 is 6x10(16) cm(-3) emphasizing its relevance for carrier statistics and applications.

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Quantum systems can provide outstanding performance in various sensing applications, ranging from bioscience to nanotechnology. Atomic-scale defects in silicon carbide are very attractive in this respect because of the technological advantages of this material and favorable optical and radio frequency spectral ranges to control these defects. We identified several, separately addressable spin-3/2 centers in the same silicon carbide crystal, which are immune to nonaxial strain fluctuations. Some of them are characterized by nearly temperature independent axial crystal fields, making these centers very attractive for vector magnetometry. Contrarily, the zero-field splitting of another center exhibits a giant thermal shift of −1.1 MHz/K at room temperature, which can be used for thermometry applications. We also discuss a synchronized composite clock exploiting spin centers with different thermal response.

We uncover the fine structure of a silicon vacancy in isotopically purified silicon carbide (4H-28 SiC) and reveal not yet considered terms in the spin Hamiltonian, originated from the trigonal pyramidal symmetry of this spin-3/2 color center. These terms give rise to additional spin transitions, which would be otherwise forbidden, and lead to a level anticrossing in an external magnetic field. We observe a sharp variation of the photoluminescence intensity in the vicinity of this level anticrossing, which can be used for a purely all-optical sensing of the magnetic field. We achieve dc magnetic field sensitivity better than 100 nT/ √ Hz within a volume of 3 × 10 −7 mm 3 at room temperature and demonstrate that this contactless method is robust at high temperatures up to at least 500 K. As our approach does not require application of radiofrequency fields, it is scalable to much larger volumes. For an optimized light-trapping waveguide of 3 mm 3 the projection noise limit is below 100 fT/ √ Hz.

Several systems in the solid state have been suggested as promising candidates for spin-based quantum information processing. In spite of significant progress during the last decade, there is a search for new systems with higher potential [D. DiVincenzo, Nature Mat. 9, 468 (2010)]. We report that silicon vacancy defects in silicon carbide comprise the technological advantages of semiconductor quantum dots and the unique spin properties of the nitrogen-vacancy defects in diamond. Similar to atoms, the silicon vacancy qubits can be controlled under the double radio-optical resonance conditions, allowing for their selective addressing and manipulation. Furthermore, we reveal their long spin memory using pulsed magnetic resonance technique. All these results make silicon vacancy defects in silicon carbide very attractive for quantum applications.PACS numbers: 61.72. Hh, 76.70.Hb, 61.72.jd The double radio-optical resonance in atoms [1] constitutes the basis for a unprecedented level of coherent quantum control. Atomic time standards [2] and multiqubit quantum logic gates [3] are among the most known examples. In the solid state, semiconductor quantum dots (QDs) and the nitrogen-vacancy (NV) defects in diamond, frequently referred to as artificial atoms, are considered as the most promising candidates for quantum information processing [4,5]. Nevertheless, such a high degree of quantum control, as achieved in atoms,has not yet been demonstrated in these systems so far. Therefore, there is a search for quantum systems with even more potential [6].Recently, intrinsic defects in silicon carbide (SiC) have been proposed as eligible candidates for qubits [7,8]. Indeed, they reveal quantum spin coherence even at room temperature [9][10][11]. All of these experiments have been carried out under non-resonant optical excitation where all spins are controlled simultaneously. However, for spinbased information processing it is necessary to perform manipulations of selected spins, while the rest should remain unaffected. This demonstration in SiC is still an outstanding task.The selective spin control can be realized using a resonant optical excitation. As a rule, inhomogeneous broadening is much larger than the natural spectral linewidth, and such resonant addressing can be done on single centers only. To avoid this problem, we applied a special procedure to "freeze" silicon vacancy (V Si ) defects during their growth, allowing to preserve a high homogeneity inherent to Lely crystals. This is confirmed by the extremely sharp optical resonances in our samples. The spectral width of the V Si absorption lines is several µeV (ca. 1 GHz), which comparable with that of a single QD or a single NV center in diamond.We then demonstrate the selective spin initialization and readout by tuning the laser wavelength together with the spin manipulation by means of electron spin resonance (ESR). Such a double radio-optical resonance control indicates that the V Si defects strongly interact with light and are well decoupled from lattice vibr...

We report the realization of the optically induced inverse population of the ground-state spin sublevels of the silicon vacancies (V(Si)) in silicon carbide (SiC) at room temperature. The data show that the probed silicon vacancy spin ensemble can be prepared in a coherent superposition of the spin states. Rabi nutations persist for more than 80 μs. Two opposite schemes of the optical alignment of the populations between the ground-state spin sublevels of the silicon vacancy upon illumination with unpolarized light are realized in 4H- and 6H-SiC at room temperature. These altogether make the silicon vacancy in SiC a very favorable defect for spintronics, quantum information processing, and magnetometry.

We report a giant thermal shift of 2.1 MHz/K related to the excited-state zero-field splitting in the silicon vacancy centers in 4H silicon carbide. It is obtained from the indirect observation of the optically detected magnetic resonance in the excited state using the ground state as an ancilla. Alternatively, relative variations of the zero-field splitting for small temperature differences can be detected without application of radiofrequency fields, by simply monitoring the photoluminescence intensity in the vicinity of the level anticrossing. This effect results in an all-optical thermometry technique with temperature sensitivity of 100 mK/Hz1/2 for a detection volume of approximately 10−6 mm3. In contrast, the zero-field splitting in the ground state does not reveal detectable temperature shift. Using these properties, an integrated magnetic field and temperature sensor can be implemented on the same center.