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The nitrogen-vacancy center (N-V center) is one of numerous point defects in diamond. Its most explored and useful property is photoluminescence, which can be easily detected from an individual N-V center, especially those in the negative charge state (N-V−). Electron spins at N-V centers, localized at atomic scales, can be manipulated at room temperature by applying a magnetic field, electric field, microwave radiation or light, or a combination, resulting in sharp resonances in the intensity and wavelength of the photoluminescence. These resonances can be explained in terms of electron spin related phenomena such as quantum entanglement, spin-orbit interaction and Rabi oscillations, and analysed using advanced quantum optics theory. An individual N-V center can be viewed as a basic unit of a quantum computer, and it has potential applications in novel, more efficient fields of electronics and computational science including quantum cryptography and spintronics. ==Structure== The nitrogen-vacancy center is a point defect in the diamond lattice. It consists of a nearest-neighbor pair of a nitrogen atom, which substitutes for a carbon atom, and a lattice vacancy. Two charge states of this defect, neutral N-V0 and negative N-V−, are known from spectroscopic studies using optical absorption,〔 〕〔 〕 photoluminescence (PL),〔 〕 electron paramagnetic resonance (EPR)〔 〕〔 〕〔 〕 and optically detected magnetic resonance (ODMR),〔 which can be viewed as a hybrid of PL and EPR; most details of the structure originate from EPR. A nitrogen atom has five valence electrons. Three of them covalently bond to the carbon atoms and two remain non-bonded and are called a lone pair. The vacancy has three unpaired electrons. Two of them make a quasi covalent bond and one remains unpaired. The overall symmetry, however, is axial (trigonal C3V); one can visualize this by imagining the three unpaired vacancy electrons continuously exchanging their roles. The N-V0 thus has one unpaired electron and is paramagnetic. However, despite extensive efforts, electron paramagnetic resonance signals from N-V0 avoided detection for decades until 2008. Optical excitation is required to bring the N-V0 defect into the EPR-detectable excited state; the signals from the ground state are presumably too broad for EPR detection.〔 〕 In the negative charge state N-V−, an extra electron is located at the vacancy site forming a spin S=1 pair with one of the vacancy electrons. As in N-V0, the vacancy electrons are "exchanging roles" preserving the overall trigonal symmetry. This N-V− state is what is commonly, and somewhat incorrectly, called "the nitrogen-vacancy center". The neutral state has not yet been explored for spin manipulations. The N-V centers are randomly oriented within a diamond crystal. Ion implantation techniques can enable their artificial creation in predetermined positions.〔 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Nitrogen-vacancy center」の詳細全文を読む スポンサード リンク
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