Norikazu Mizuochi

Nanodiamond quantum sensors have been regarded as promising probes for cellular thermometry, but their poor sensor-to-sensor reproducibility has hindered practical implementation. In cellular measurements, the resulting temperature-readout offsets can be mistaken for real cell-to-cell temperature differences, limiting quantitative comparison. Here, we show that spin-uniform nitrogen vacancy (NV)-rich nanodiamonds can be produced via postenrichment oxidative size reduction, which removes defective surface layers while improving crystallinity. Compared with nanodiamonds prepared by conventional mechanical milling before NV enrichment, the particle-to-particle spread in the temperature-sensitive D values was reduced by 3.7-fold. The improved NV homogeneity also enhanced spin properties: the optically detected magnetic resonance contrast─a key signal amplitude for sensitivity─increased by more than 50%. Together, these improvements reduce cell-to-cell dispersion in D-derived single-cell temperature readouts to below 0.7 K, enabling reliable temperature comparison across cells. This approach advances nanodiamond absolute thermometry toward organelle-scale intracellular temperature mapping and practical quantum sensing in biology and medicine.

Defect charge-state dynamics are central to both spin−photon interfaces and photoelectrical spin readout. Despite the significance of silicon vacancies (V1/V2) in silicon carbide (4H-SiC) for both applications, their ionization behavior has remained unclear because conventional optical charge-state analysis is prevented by undetectable optical blinking. Here, we employ photocurrent spectroscopy of individual defects to measure the wavelength-dependent ionization cross sections. We reveal similar ionization cross sections for V1 and V2, increasing toward shorter wavelengths, while carbon vacancies dominate the more steeply increasing background photocurrent. These results indicate that, under resonant excitation at the respective ZPLs, V2 is less susceptible to photoionization, and its surrounding background defects are less ionized than V1. We also identify wavelength regimes that optimize defect-origin photocurrent for photoelectrical spin readout relative to background contributions, which differ between single-defect and ensemble measurements. Our results establish photocurrent spectroscopy as a powerful complement to optical methods, advancing defect-based quantum device development.

The development of quantum technology is facing substantial scientific and technological challenges. More importantly, there are as-yet-unknown aspects and applications of quantum technology to be uncovered. There is thus global acknowledgement by stakeholder communities and governments alike that the ongoing advancement of quantum science and technology ought to be an international pursuit in which the strain between competition and cooperation is balanced through collaboration. It is in this spirit of “coopetition” that this article seeks to give a cross-sectional view of the state of Quantum 2.0 technology in the USA, Europe and Japan, by providing the predictions of a large number of experts concerning progress in quantum technology over the next two decades.

We investigated the spatial resolution of scanning photocurrent microscopy (SPhM) for imaging single nitrogen-vacancy (NV) centers in diamond in detail and compared it with that of confocal laser scanning microscopy (CLSM). While CLSM suffers from degraded spatial resolution due to fluorescence saturation, SPhM maintains a high spatial resolution despite the high-power laser excitation required. Numerical simulations of SPhM and CLSM images showed good agreement with experimental data and further indicated that SPhM achieves superior spatial resolution. Additionally, the signal-to-noise ratio of the photoelectrically detected magnetic resonance spectrum is comparable to that of the optically detected magnetic resonance spectrum in our home-made spectrometers. These findings suggest that SPhM can enhance the performance of NV-based quantum sensors.

We developed a compact, portable quantum sensor module for pulsed measurements using diamond nitrogen-vacancy (NV) centers, an excitation laser diode of 3 mW and a microwave source of 15 dBm. This module allowed the evaluation of ensemble diamond NV centers for measuring magnetic fields by continuous wave— optically detected magnetic resonance (ODMR), Rabi oscillation, pulsed ODMR, Ramsey measurement and spin-echo measurement. The sensitivity through pulsed measurements reached 40 nT/ Hz at 1 Hz, which achieved higher sensitivity by one order, especially at a frequency around 1 Hz compared with previously reported compact modules using diamond NV centers.

Group-IV color centers in diamonds are promising not only as spin–photon interfaces for quantum networks but also as multicolor photoluminescence probes and all-optical temperature sensors for biological research. Therefore, generating group-IV color centers in detonation nanodiamonds (DNDs), the smallest class of diamond nanocrystals, has become a research focal point. This approach holds potential for the noninvasive introduction of diamond sensors into living cell organelles, enabling sensing of local structural and temperature changes with minimal disturbance. Following the successful generation of silicon- and germanium-vacancy centers in DNDs, the generation of tin-vacancy (SnV) centers was investigated. Similar to other group-IV color centers, the SnV centers exhibit strong photoluminescence. In addition, the SnV center offers a long spin coherence time compared with those of silicon- and germanium-vacancy centers. However, the strain induced by large Sn atoms poses substantial challenges for generating SnV centers in ultrasmall nanodiamonds. In this study, Sn-doped DNDs with a mean particle size of ~ 5 nm were subjected to a 3 days boiling acid treatment, which led to sharp zero-phonon lines of SnV centers at ~ 620 nm in the photoluminescence spectra. Photon autocorrelation measurements further revealed the presence of single SnV centers in these DNDs.

We present a method to directly detect the axion dark matter using nitrogen vacancy centers in diamonds. In particular, we use metrology leveraging the nuclear spin of nitrogen to detect axion-nucleus couplings. This is achieved through protocols designed for dark matter searches, which introduce a novel approach of quantum sensing techniques based on the nitrogen vacancy center. Although the coupling strength of the magnetic fields with nuclear spins is three orders of magnitude smaller than that with electron spins for conventional magnetometry, the axion interaction strength with nuclear spins is the same order of magnitude as that with electron spins. Furthermore, we can take advantage of the long coherence time by using the nuclear spins for the axion dark matter detection. Our method has the potential to be sensitive to a broad frequency range ≲ 100 Hz corresponding to the axion mass m a ≲ 4 × 10 − 13 eV . We present the detection limit of our method for both the axion-neutron and the axion-proton couplings and discuss its significance in comparison with other proposed ideas. We also show that the sensitivities of the NV center sensor to various spin species will open up new directions for constructing protocols that can mitigate magnetic noise effects.

Establishing a robust and integratable quantum system capable of sensitive qubit readout at ambient conditions is a key challenge for developing prevalent quantum technologies, including quantum networks and quantum sensing. Paramagnetic colour centres in wide bandgap semiconductors provide optical single-spin detection, yet realising efficient electrical readout technology in scalable material will unchain developing integrated ambient quantum electronics. Here, we demonstrate photoelectrical detection of single spins in silicon carbide, a material amenable to large-scale processing and electronic integration. With efficient photocarrier collection, we achieve a 1.7–2 times better signal-to-noise ratio for single spins of silicon vacancies with electrical detection than with optical detection suffering from saturating fluorescence and internal reflection. Based on our photoionisation dynamics study, further improvement would be expected with enhanced ionisation. We also observe single-defect-like features in the photocurrent image where photoluminescence is absent in the spectrum range of silicon vacancies. The efficient electrical readout in the mature material platform holds promise for developing integrated quantum devices.