Solid-state single spins are promising resources for quantum sensing, quantum-information processing and quantum networks, because they are compatible with scalable quantum-device engineering. However, the extension of their coherence times proves challenging. Although enrichment of the spin-zero 12 C and 28 Si isotopes drastically reduces spin-bath decoherence in diamond and silicon, the solid-state environment provides deleterious interactions between the electron spin and the remaining spins of its surrounding. Here we demonstrate, contrary to widespread belief, that an impurity-doped (phosphorus) n-type single-crystal diamond realises remarkably long spin-coherence times. Single electron spins show the longest inhomogeneous spin-dephasing time ( ms) and Hahn-echo spin-coherence time ( T 2 ≈ 2.4 ms) ever observed in room-temperature solid-state systems, leading to the best sensitivities. The extension of coherence times in diamond semiconductor may allow for new applications in quantum technology.

Magnetic field sensors based on organic thin-film materials have attracted considerable interest in recent years as they can be manufactured at very low cost and on flexible substrates. However, the technological relevance of such magnetoresistive sensors is limited owing to their narrow magnetic field ranges (∼30 mT) and the continuous calibration required to compensate temperature fluctuations and material degradation. Conversely, magnetic resonance (MR)-based sensors, which utilize fundamental physical relationships for extremely precise measurements of fields, are usually large and expensive. Here we demonstrate an organic magnetic resonance-based magnetometer, employing spin-dependent electronic transitions in an organic diode, which combines the low-cost thin-film fabrication and integration properties of organic electronics with the precision of a MR-based sensor. We show that the device never requires calibration, operates over large temperature and magnetic field ranges, is robust against materials degradation and allows for absolute sensitivities of <50 nT Hz−1/2.

Nitrogen-vacancy (NV) centers in diamond have attracted significant interest because of their excellent spin and optical characteristics for quantum information and metrology. To take advantage of the characteristics, the precise control of the orientation of the N-V axis in the lattice is essential.Here we show that the orientation of more than 99 % of the NV centers can be aligned along the [111]axis by CVD homoepitaxial growth on (111)-substrates. We also discuss about mechanisms of the alignment. Our result enables a fourfold improvement in magnetic-field sensitivity and opens new avenues to the optimum design of NV center devices.

Apart from applications in classical information-processing devices, the electrical control of atomic defects in solids at room temperature will have a tremendous impact on quantum devices that are based on such defects. In this study, we demonstrate the electrical manipulation of individual prominent representatives of such atomic solid-state defects, namely, the negative charge state of single nitrogenvacancy defect centers (NV −) in diamond. We experimentally demonstrate, deterministic, purely electrical charge-state initialization of individual NV centers. The NV centers are placed in the intrinsic region of a p-in diode structure that facilitates the delivery of charge carriers to the defect for charge-state switching. The charge-state dynamics of a single NV center were investigated by time-resolved measurements and a nondestructive single-shot readout of the charge state. Fast charge-state switching rates (from negative to neutrally charged defects), which are greater than 0.72 AE 0.10 μs −1 , were realized. Furthermore, in no-operation mode, the realized charge states were stable for presumably much more than 0.45 s. We believe that the results obtained are useful not only for ultrafast electrical control of qubits, long T 2 quantum memory, and quantum sensors associated with single NV centers but also for classical memory devices based on single atomic storage bits working under ambient conditions.

17Optical illumination to negatively charged nitrogen-vacancy centers (NV − ) inevitably causes 18 stochastic charge-state transitions between NV − and neutral charge state of the NV center.It limits the 19 steady-state-population of NV − to 5% at minimum (~610 nm) and 80% (~532 nm) at maximum in 20 intrinsic diamond depending on the wavelength.. Here, we show Fermi level control by phosphorus 21 doping generates 99.4 ± 0.1% NV − under 1 μW and 593 nm excitation which is close to maximum 22 absorption of NV − . The pure NV − shows a five-fold increase of luminescence and a four-fold 23 enhancement of an optically detected magnetic resonance under 593 nm excitation compared with 24 those in intrinsic diamond. 25 26 27

Electron paramagnetic resonance of ensembles of phosphorus donors in silicon has been detected electrically with externally applied magnetic fields lower than 200 G. Because the spin Hamiltonian was dominated by the contact hyperfine term rather than by the Zeeman terms at such low magnetic fields, superposition states α |↑↓ + β |↓↑ and −β |↑↓ + α |↓↑ were formed between phosphorus electron and nuclear spins, and electron paramagnetic resonance transitions between these superposition states and |↑↑ or |↓↓ states are observed clearly. A continuous change of α and β with the magnetic field was observed with a behavior fully consistent with theory of phosphorus donors in silicon.

Optically detected magnetic resonance (ODMR) is a way to characterize the NV − centers. Recently, a remarkably sharp dip was observed in the ODMR with a high-density ensemble of NV centers, and this was reproduced by a theoretical model in [Zhu et al., Nature Communications 5, 3424 (2014)], showing that the dip is a consequence of the spin-1 properties of the NV − centers. Here, we present much more details of analysis to show how this model can be applied to investigate the properties of the NV − centers. By using our model, we have reproduced the ODMR with and without applied magnetic fields. Also, we theoretically investigate how the ODMR is affected by the typical parameters of the ensemble NV − centers such as strain distributions, inhomogeneous magnetic fields, and homogeneous broadening width. Our model could provide a way to estimate these parameters from the ODMR, which would be crucial to realize diamond-based quantum information processing.

The charge-state control of nitrogen-vacancy (NV) centers in diamond is very important toward its applications because the NV centers undergo stochastic charge-state transitions between the negative charge state (NV À ) and the neutral charge state (NV 0 ) of the NV center upon illumination. In this letter, engineering of the Fermi level by a nin diamond junction was demonstrated for the control of the charge state of the NV centers in the intrinsic (i) layer region. By changing the size (d) of the i-layer region between the phosphorus-doped n-type layer regions (nin) from 2 lm to 10 lm, we realized the gradual change in the NV À charge-state population in the i-layer region from 60% to 80% under 532 nm excitation, which can be attributed to the band bending in the i-layer region. Also, we quantitatively simulated the changes in the Fermi level in the i-layer region depending on d with various concentrations of impurities in the i-layer region.