Spin-Dependent Dynamics of Photocarrier Generation in Electrically Detected Nitrogen-Vacancy-Based Quantum Sensing

Electrical detection of nitrogen-vacancy (N-V) centers in diamond is advantageous for developing and integrating quantum information processing devices and quantum sensors and has the potential to achieve a higher collection efficiency than that of optical techniques. However, the mechanism for the electrical detection of N-V spins is not fully understood. In this study, we observe positive contrast in photocurrent detected magnetic resonance (PDMR). Note that negative PDMR contrast is usually observed. To discuss the sign of the PDMR contrast, we numerically analyze the dynamics of photocarrier generation by N-V centers using a seven-level rate model. It is found that the sign of the PDMR contrast depends on the difference in the photocurrent generated from the excited states and the metastable state of N-V centers. Furthermore, we demonstrate ac magnetic field sensing using spin coherence with the PDMR technique. ac magnetic field measurement with the PDMR technique is still challenging because the noise from a fluctuating magnetic environment is greater than the measured signal. Here, we introduce noise suppression using a phase-cycling-based noise-canceling technique. We demonstrate electrically detected ac magnetic field sensing with a sensitivity of 29 nT Hz[−1/2]. Finally, we discuss sensitivity enhancement based on the proposed model

Coherent electrical readout of defect spins in 4H-SiC by photo-ionization at ambient conditions

Quantum technology relies on proper hardware, enabling coherent quantum state control as well as efficient quantum state readout. In this regard, wide-bandgap semiconductors are an emerging material platform with scalable wafer fabrication methods, hosting several promising spin-active point defects. Conventional readout protocols for such defect spins rely on fluorescence detection and are limited by a low photon collection efficiency. Here, we demonstrate a photo-electrical detection technique for electron spins of silicon vacancy ensembles in the 4H polytype of silicon carbide (SiC). Further, we show coherent spin state control, proving that this electrical readout technique enables detection of coherent spin motion. Our readout works at ambient conditions, while other electrical readout approaches are often limited to low temperatures or high magnetic fields. Considering the excellent maturity of SiC electronics with the outstanding coherence properties of SiC defects the approach presented here holds promises for scalability of future SiC quantum devices

Small multimodal thermometry with detonation-created multi-color centers in detonation nanodiamond

微小ナノダイヤモンド量子センサで安定的に温度計測実現--細胞内などの微小領域での量子センシングに期待--.京都大学プレスリリース. 2024-05-16.Detonation nanodiamond (DND) is the smallest class of diamond nanocrystal capable of hosting various color centers with a size akin to molecular pores. Their negatively charged nitrogen-vacancy center (NV⁻) is a versatile tool for sensing a wide range of physical and even chemical parameters at the nanoscale. The NV⁻ is, therefore, attracting interest as the smallest quantum sensor in biological research. Nonetheless, recent NV⁻ enhancement in DND has yet to yield sufficient fluorescence per particle, leading to efforts to incorporate other group-IV color centers into DND. An example is adding a silicon dopant to the explosive mixture to create negatively charged silicon-vacancy centers (SiV⁻). In this paper, we report on efficient observation (∼50% of randomly selected spots) of the characteristic optically detected magnetic resonance (ODMR) NV⁻ signal in silicon-doped DND (Si-DND) subjected to boiling acid surface cleaning. The NV⁻ concentration is estimated by continuous-wave electron spin resonance spectroscopy to be 0.35 ppm without the NV⁻ enrichment process. A temperature sensitivity of 0.36 K/√HZ in an NV⁻ ensemble inside an aggregate of Si-DND is achieved via the ODMR-based technique. Transmission electron microscopy survey reveals that the Si-DNDs core sizes are ∼11.2 nm, the smallest among the nanodiamond’s temperature sensitivity studies. Furthermore, temperature sensing using both SiV⁻ (all-optical technique) and NV⁻ (ODMR-based technique) in the same confocal volume is demonstrated, showing Si-DND’s multimodal temperature sensing capability. The results of the study thereby pave a path for multi-color and multimodal biosensors and for decoupling the detected electrical field and temperature effects on the NV⁻ center

Electrical Charge State Manipulation of Single Silicon Vacancies in a Silicon Carbide Quantum Optoelectronic Device

Colour centres with long-lived spins are established platforms for quantum sensing and quantum information applications. Colour centres exist in different charge states, each of them with distinct optical and spin properties. Application to quantum technology requires the capability to access and stabilize charge states for each specific task. Here, we investigate charge state manipulation of individual silicon vacancies in silicon carbide, a system which has recently shown a unique combination of long spin coherence time and ultrastable spin-selective optical transitions. In particular, we demonstrate charge state switching through the bias applied to the colour centre in an integrated silicon carbide opto-electronic device. We show that the electronic environment defined by the doping profile and the distribution of other defects in the device plays a key role for charge state control. Our experimental results and numerical modeling evidence that control of these complex interactions can, under certain conditions, enhance the photon emission rate. These findings open the way for deterministic control over the charge state of spin-active colour centres for quantum technology and provide novel techniques for monitoring doping profiles and voltage sensing in microscopic devices

Spectrally reconfigurable quantum emitters enabled by optimized fast modulation

The ability to shape photon emission facilitates strong photon-mediated interactions between disparate physical systems, thereby enabling applications in quantum information processing, simulation and communication. Spectral control in solid state platforms such as color centers, rare earth ions, and quantum dots is particularly attractive for realizing such applications on-chip. Here we propose the use of frequency-modulated optical transitions for spectral engineering of single photon emission. Using a scattering-matrix formalism, we find that a two-level system, when modulated faster than its optical lifetime, can be treated as a single-photon source with a widely reconfigurable photon spectrum that is amenable to standard numerical optimization techniques. To enable the experimental demonstration of this spectral control scheme, we investigate the Stark tuning properties of the silicon vacancy in silicon carbide, a color center with promise for optical quantum information processing technologies. We find that the silicon vacancy possesses excellent spectral stability and tuning characteristics, allowing us to probe its fast modulation regime, observe the theoretically-predicted two-photon correlations, and demonstrate spectral engineering. Our results suggest that frequency modulation is a powerful technique for the generation of new light states with unprecedented control over the spectral and temporal properties of single photons.Comment: 9 pages, 6 figures; Supplementary Informatio

表面平坦化処理を施したSiナノワイヤMOSFETにおけるキャリヤ輸送の基礎研究

京都大学0048新制・課程博士博士(工学)甲第18286号工博第3878号新制||工||1595(附属図書館)31144京都大学大学院工学研究科電子工学専攻(主査)教授 木本 恒暢, 教授 白石 誠司, 准教授 浅野 卓学位規則第4条第1項該当Doctor of Philosophy (Engineering)Kyoto UniversityDFA

Bandgap shift by quantum confinement effect in <100> Si-nanowires derived from threshold-voltage shift of fabricated metal-oxide-semiconductor field effect transistors and theoretical calculations

Si-nanowire (Si-NW) MOSFETs, the cross-sectional size (square root of the cross-sectional area of NWs) of which was changed from 18 to 4 nm, were fabricated and characterized. Both n- and p-channel MOSFETs have shown a nearly ideal subthreshold swing of 63 mV/decade. The threshold voltage of n-/p-channel MOSFETs has gradually increased/decreased with decreasing the cross-sectional size. The bandgap shift from bulk Si has been derived from the threshold-voltage shift. The bandgap of Si-NWs was calculated by a density functional theory, tight binding method, and effective mass approximation. The calculated bandgap shows good agreement with that derived from threshold voltage. The theoretical calculation indicates that the bandgap is dominated by the cross-sectional size (area) and is not very sensitive to the shape within the aspect-ratio range of 1.0-2.5

Quantum-confinement effect on holes in silicon nanowires: Relationship between wave function and band structure

The authors theoretically studied the valence band structure and hole effective mass of rectangular cross-sectional Si nanowires (NWs) with the crystal orientation of [110], [111], and [001]. The E–k dispersion and the wave function were calculated using an sp^3d^5s∗ tight-binding method and analyzed with the focus on the nature of p orbitals constituting the subbands. In [110] and [111] nanowires, longitudinal/transverse p orbitals are well separated and longitudinal component makes light (top) subbands and transverse component makes heavy subbands. The heavy subbands are located far below the top light band when NW has square cross-section, but they gain their energy with the increase in the NW width and come near the band edge. This energy shift of heavy bands in [110] NWs shows strong anisotropy to the direction of quantum confinement whereas that in [111] NWs does not have such anisotropy. This anisotropic behavior and the difference among orientations are understandable by the character of the wave function of heavy subbands. Regarding the [001] nanowires, the top valence state is formed by the mixture of longitudinal/transverse p orbitals, which results in heavy effective mass and large susceptibility to lateral-size variation. The correlation of the wave function of hole states between nanowires and bulk is also discussed briefly