Atomic-sized fluorescent defects in diamond are widely recognized as a promising solid state platform for quantum cryptography and quantum information processing. For these applications, single photon sources with a high intensity and reproducible fabrication methods are required. In this study, we report a novel color center in diamond, composed of a germanium (Ge) and a vacancy (V) and named the GeV center, which has a sharp and strong photoluminescence band with a zero-phonon line at 602 nm at room temperature. We demonstrate this new color center works as a single photon source. Both ion implantation and chemical vapor deposition techniques enabled fabrication of GeV centers in diamond. A first-principles calculation revealed the atomic crystal structure and energy levels of the GeV center.

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

Nitrogen-vacancy (NV) centers in diamond have attracted a great deal of attention because of their possible use in information processing and electromagnetic sensing technologies. We examined the atomistic generation mechanism for the NV defect aligned in the [111] direction of C(111) substrates. We found that N is incorporated in the C bilayers during the lateral growth arising from a sequence of kink propagation along the step edge down to [112]. As a result, the atomic configuration with the N-atom lone-pair pointing in the [111] direction is formed, which causes preferential alignment of NVs. Our model is consistent with recent experimental data for perfect NV alignment in C(111) substrates. PACS numbers: 81.05.ug, 68.35.Dv, 81.10.Aj Nitrogen-vacancy (NV) centers in diamond [1] have been recognized as representative examples of entangled S=1 systems in solid-state materials. Because of the externally controllable entanglement between the electronic and nuclear spin states [2-4] and excellent coherence properties in time [5] as well as space [6], numerous technological applications of the NV centers have been demonstrated to date [7-23].An NV center in a diamond crystal is composed of an N atom substituting for a carbon atom with an adjacent carbon vacancy (V) sitting in various orientations relative to N. For example, the NVs near the C(111) surface could have eight possible NV orientations, four with N in one sublattice in the bilayer [α layer, Fig. 1 (a)] and the remaining four with N in the other sublattice [β layer, Fig. 1 (b)].For practical applications, it is desirable to have the NV orientations aligned in one direction. In spindependent NV fluorescence experiments in C(001) samples grown by chemical vapor deposition (CVD), the magnetic field sensitivity was doubled relative to samples with random NV orientations [24]. This was because most of NV centers were arranged in two of four possible orientations. The partial alignment of the NV centers was also reported for CVD grown (110) substrates [25]. Recently, various groups [26-28] have reported the nearly perfect alignment of the NV centers along the [111] direction in C(111) samples grown by CVD (94%±2% [26], ∼97% [27], and ≥99% [28] relative to the total number of NVs generated). The formation mechanism was * Electronic address: takehide.miyazaki@aist.go.jp explained in terms of the step-flow growth [27] in a similar way to the (110) case [25]. A first-principles study published prior to these experiments predicted that V and N are in the first and second layers, respectively [ Fig. 1 (b)] [29]. Although the theory also discussed how the N is located in the α layer [ Fig. 1 (a)], the atomistic reason for the selective NV alignment in [111] [26-28] is still unknown.In this study we address this question by using firstprinciples energetics. We found that the N incorporated at the kink site of the [112] step edge is embedded in the subsurface in a sequence of kink-flows along this step and finally becomes the [111]-oriented NV center. Our theoretical...