Search Results (106)

Nitrogen vacancy (NV) diamonds are promising room temperature quantum sensors. As the technology moves towards application, efficient use of energy and cost become critical for miniaturization. This work focuses on microwave-based spin control using the short-circuited end of a slot line, analyzed by finite element method (FEM) for magnetic field amplitude and uniformity. A microstrip-to-slot-line converter with a $-10$ dB bandwidth of $3.2$ GHz was implemented. Rabi oscillation measurements with an NV microdiamond on a glass fiber show uniform excitation over $1.5$ MHz across the slot, allowing spin manipulation within the coherence time of the NV center. Full article

We provide an approach to detect a nitrogen-vacancy (NV) center, which might be a defect in a diamond nanomembrane, using a dual-coupling optomechanical system. The NV center modifies the energy-level structure of a dual-coupling optomechanical system through dressed states arising from its interaction with the mechanical membrane. Thus, we study the photon blockade in the cavity of a dual-coupling optomechanical system in which an NV center is embedded in a single-crystal diamond nanomembrane. The NV center significantly influences the statistical properties of the cavity field. We systematically investigate how three key NV center parameters affect photon blockade: (i) its coupling strength to the mechanical membrane, (ii) transition frequency, and (iii) decay rate. We find that the NV center can shift, give rise to a new dip, and even suppress the original dip in a bare quadratic optomechanical system. In addition, we can amplify the effect of the NV center on photon statistics by adding a gravitational potential when the NV center has little effect on photon blockade. Therefore, our study provides a method to detect diamond nanomembrane defects in a dual-coupling optomechanical system. Full article

The efficient depolymerization of lignin has become a key challenge in the preparation of high-value-added chemicals. Graphitic carbon nitride (g-C₃N₄)-based photocatalytic system shows potential due to its mild and green characteristics over other depolymerization methods. However, its inherent defects, such as a wide band gap and rapid carrier recombination, severely limit its catalytic performance. In this paper, a g-C₃N₄ modification strategy of K⁺ doping and surface alkalinization is proposed, which is firstly applied to the photocatalytic depolymerization of the lignin β-O-4 model compound (2-phenoxy-1-phenylethanol). K⁺ doping is achieved by introducing KCl in the precursor thermal polymerization stage to weaken the edge structure strength of g-C₃N₄, and post-treatment with KOH solution is combined to optimize the surface basic groups. The structural/compositional evolution of the materials was analyzed by XRD, FTIR, and XPS. The morphology/element distribution was visualized by SEM-EDS, and the optoelectronic properties were evaluated by UV–vis DRS, PL, EIS, and transient photocurrent (TPC). K⁺ doping and surface alkalinization synergistically regulate the layered structure of the material, significantly increase the specific surface area, introduce nitrogen vacancies and hydroxyl functional groups, effectively narrow the band gap (optimized to 2.35 eV), and inhibit the recombination of photogenerated carriers by forming electron capture centers. Photocatalytic experiments show that the alkalinized g-C₃N₄ can completely depolymerize 2-phenoxy-1-phenylethanol with tunable product selectivity. By adjusting reaction time and catalyst dosage, the dominant product can be shifted from benzaldehyde (up to 77.28% selectivity) to benzoic acid, demonstrating precise control over oxidation degree. Mechanistic analysis shows that the surface alkaline sites synergistically optimize the C_β-O bond breakage path by enhancing substrate adsorption and promoting the generation of active oxygen species (·OH, ·O₂⁻). This study provides a new idea for the efficient photocatalytic depolymerization of lignin and lays an experimental foundation for the interface engineering and band regulation strategies of g-C₃N₄-based catalysts. Full article

Color centers in solids, such as nitrogen-vacancy (NV) centers in diamonds, have gained significant attention in recent years due to their exceptional properties for quantum sensing. In this work, we demonstrate an NV center-based temperature sensor integrated into an optical waveguide to enable internal temperature sensing. A surface-cladding optical waveguide was fabricated in a diamond wafer containing NV centers using femtosecond laser direct writing. By analyzing the resonant peaks of optically detected magnetic resonance (ODMR) spectra, we established a precise correlation between temperature changes induced by the pump laser and shifts in the ODMR peak positions. This approach enabled temperature monitoring with a sensitivity of 1.1 $\mathrm{mK}/\sqrt{\mathrm{Hz}}$. These results highlight the significant potential of color centers in solids for non-contact, micro-scale temperature monitoring. Full article

Thulium iron garnet (Tm₃Fe₅O₁₂, TmIG) is a promising material for next-generation spintronic and quantum technologies owing to its high Curie temperature and strong perpendicular magnetic anisotropy. However, conventional magnetometry techniques are limited by insufficient spatial resolution and sensitivity to probe local magnetic phase transitions and critical spin dynamics in thin films. In this study, we present the first quantitative investigation of local magnetic field fluctuations near the Curie temperature in TmIG thin films using nitrogen-vacancy (NV) center-based quantum sensing. By integrating optically detected magnetic resonance (ODMR) and NV spin relaxometry (T₁ measurements) with macroscopic techniques such as SQUID magnetometry and Hall effect measurements, we systematically characterize both the static magnetization and dynamic spin fluctuations across the magnetic phase transition. Our results reveal a pronounced enhancement in NV spin relaxation rates near 360 K, providing direct evidence of critical spin fluctuations at the nanoscale. This work highlights the unique advantages of NV quantum sensors for investigating dynamic critical phenomena in complex magnetic systems and establishes a versatile, multimodal framework for studying local phase transition kinetics in high-temperature magnetic insulators. Full article

With the development of chip technology, the demand for device reliability in various electronic chip industries continues to grow. In recent years, with the advancement of quantum sensors, the solid-state spin (nitrogen-vacancy) NV center temperature measurement system has garnered attention due to its high sensitivity and spatial range. However, NV centers are not only affected by temperature but also by magnetic fields. This article analyzes the impact of magnetic fields on temperature detection. By combining the wide-field imaging platform of optically detected magnetic resonance (ODMR) with a temperature-sensitive structure of thin ensemble diamond overlaid on a quartz substrate, high-sensitivity temperature detection has been achieved. And obtains a sensitivity of approximately 10 mK/Hz^1/2. By combining a CCD camera imaging system, it realizes a wide field of view of 500 μm², a high spatial resolution of 1.3 μm. Ultimately, this study demonstrates the two-dimensional actual temperature distribution on the chip surface under different currents, achieving wide-field, non-contact, high-speed temperature imaging of the chip surface. Full article

We have developed a miniaturized magnetic sensor based on diamond nitrogen-vacancy (NV) centers, combined with a two-dimensional scanning setup that enables imaging magnetic samples with millimeter-scale resolution. Using the lock-in detection scheme, we tracked changes in the NV’s spin resonances induced by the magnetic field from target samples. As a proof-of-principle demonstration of magnetic imaging, we used a toy diorama with hidden magnets to simulate scenarios such as the remote detection of landmines on a battlefield or locating concealed objects at a construction site, focusing on image analysis rather than addressing sensitivity for practical applications. The obtained magnetic images reveal that they can be influenced and distorted by the choice of frequency point used in the lock-in detection, as well as the magnitude of the sample’s magnetic field. Through magnetic simulations, we found good agreement between the measured and simulated images. Additionally, we propose a method based on NV vector magnetometry to compensate for the non-zero tilt angles of a target, enabling the accurate localization of its position. This work introduces a novel imaging method using a scanning miniaturized magnetometer to detect hidden magnetic objects, with potential applications in military and industrial sectors. Full article

Polydispersed Ag species-modified TiO₂ samples with abundant oxygen vacancies were successfully prepared through the calcination of atomically precise Ag₃₃ nanocluster-loaded TiO₂ at an optimal temperature under a nitrogen atmosphere. The ligands of the Ag₃₃ nanoclusters are removed by extracting lattice oxygen from TiO₂ during the calcination, leading to the formation of CO₂, SO₂, and H₂O vapor. This process simultaneously induces Ag species sintering on the surface of TiO₂. The resulting nanocomposites exhibited excellent catalytic activity for the reduction of nitroarenes with NaBH₄ as the reductant. This is attributed to the produced Ag species on the oxygen-deficient TiO₂, which act as active centers for the catalytic process. Full article

Magnetoelectric (ME) devices combining piezoelectric and magnetostrictive materials have emerged as powerful tools to miniaturize and enhance sensing and communication technologies. This paper examines recent developments in bulk acoustic wave (BAW) and surface acoustic wave (SAW) ME devices, which demonstrate unique capabilities in ultra-sensitive magnetic sensing, compact antennas, and quantum applications. Leveraging the mechanical resonance of BAW and SAW modes, ME sensors achieve the femto- to pico-Tesla sensitivity ideal for biomedical applications, while ME antennas, operating at acoustic resonance, allow significant size reduction, with high radiation gain and efficiency, which is suited for bandwidth-restricted applications. In addition, ME non-reciprocal magnetoacoustic devices using hybrid magnetoacoustic waves present novel solutions for RF isolation, which have also shown potential for the efficient control of quantum defects, such as negatively charged nitrogen-vacancy (NV⁻) centers. Continued advancements in materials and device structures are expected to further enhance ME device performance, positioning them as key components in future bio-sensing, wireless communication, and quantum information technologies. Full article

This study introduces a novel method for the simultaneous detection of microwave sensor power and temperature, leveraging nitrogen-vacancy (NV) centers as a robust quantum system. Through precise measurement of the optical detection magnetic resonance contrast in NV centers, the microwave power is accurately determined. Furthermore, the temperature of the sensor is obtained by monitoring the variations in zero-field splitting and thorough spectral analysis. This method enables the efficient real-time acquisition of synchronized data on both microwave power and temperature from the sensor, facilitating concurrent monitoring without the necessity of additional sensing devices. Finally, we verified that the magnetic sensitivity of the system is approximately 1.2 nT/Hz^1/2, and the temperature sensitivity is around 0.38 mK/Hz^1/2. The minimum resolution of microwave power is about 20 nW. The experimental results demonstrate that this quantum measurement technique provides stable and accurate data across a wide range of microwave power and temperature conditions. These findings indicate substantial potential for this technique in advanced applications such as aerospace, medical diagnostics, and high-frequency communications. Future studies will aim to extend the industrial applicability of this method by refining quantum control techniques within NV center systems. Full article

A single nitrogen-vacancy (NV) center in a diamond can be used as a nanoscale sensor for magnetic field, electric field or nuclear spins. Due to its low photon detection efficiency, such sensing processes often take a long time, suffering from an electron spin resonance (ESR) frequency fluctuation induced by the time-varying thermal perturbations noise. Thus, suppressing the thermal noise is the fundamental way to enhance single-sensor performance, which is typically achieved by utilizing a thermal control protocol with a complicated and highly costly apparatus if a millikelvin-level stabilization is required. Here, we analyze the real-time thermal drift and utilize an active way to alternately track the single-spin ESR frequency drift in the experiment. Using this method, we achieve a temperature stabilization effect equivalent to sub-millikelvin (0.8 mK) level with no extra environmental thermal control, and the spin-state readout contrast is significantly improved in long-lasting experiments. This method holds broad applicability for NV-based single-spin experiments and harbors the potential for prospective expansion into diverse nanoscale quantum sensing domains. Full article

In all-optical magnetic field sensing using nitrogen-vacancy-center-rich diamonds, an ambiguity in the range of 0–8 mT can be observed. We propose a way to resolve this ambiguity using the magnetic-field-dependent fluorescence lifetime. We therefore recorded the frequency response of the fluorescence upon modulation of the excitation intensity in a frequency range of 1–$100\mathrm{MHz}$. The magnetic-field-dependent decay dynamics led to different response characteristics for magnetic fields below and above $3\mathrm{mT}$, allowing us to resolve the ambiguity. We used a physics-based model function to extract fit parameters, which we used for regression, and compared it to an alternative approach purely based on an artificial neural network. Full article

High-spin defects (color centers) in wide-gap semiconductors are considered as a basis for the implementation of quantum technologies due to the unique combination of their spin, optical, charge, and coherent properties. A silicon carbide (SiC) crystal can act as a matrix for a wide variety of optically active vacancy-type defects, which manifest themselves as single-photon sources or spin qubits. Among the defects, the nitrogen-vacancy centers (NV) are of particular importance. This paper is devoted to the application of the photoinduced electron paramagnetic resonance (EPR) and electron–nuclear double resonance (ENDOR) techniques at a high-frequency range (94 GHz) to obtain unique information about the nature and properties of NV defects in SiC crystal of the hexagonal 4H and 6H polytypes. Selective excitation by microwave and radio frequency pulses makes it possible to determine the microscopic structure of the color center, the zero-field splitting constant (D = 1.2–1.3 GHz), the phase coherence time (T₂), and the values of hyperfine (≈1.1 MHz) and quadrupole (C_q ≈ 2.45 MHz) interactions and to define the isotropic (a = −1.2 MHz) and anisotropic (b = 10–20 kHz) contributions of the electron–nuclear interaction. The obtained data are essential for the implementation of the NV defects in SiC as quantum registers, enabling the optical initialization of the electron spin to establish spin–photon interfaces. Moreover, the combination of optical, microwave, and radio frequency resonant effects on spin centers within a SiC crystal shows the potential for employing pulse EPR and ENDOR sequences to implement protocols for quantum computing algorithms and gates. Full article

The distinct spin, optical, and coherence characteristics of solid-state spin defects in semiconductors have positioned them as potential qubits for quantum technologies. Both bulk and two-dimensional materials, with varying structural properties, can serve as crystalline hosts for color centers. In this study, we conduct a comparative analysis of the spin–optical, electron–nuclear, and relaxation properties of nitrogen-bound vacancy defects using electron paramagnetic resonance (EPR) and electron–nuclear double resonance (ENDOR) techniques. We examine key parameters of the spin Hamiltonian for the nitrogen vacancy (${NV}^{-}$) center in 4H-SiC: D = 1.3 GHz, A_zz = 1.1 MHz, and C_Q = 2.53 MHz, as well as for the boron vacancy ($V_B^{-}$) in hBN: D = 3.6 GHz, A_zz = 85 MHz, and C_Q = 2.11 MHz, and their dependence on the material matrix. The spin–spin relaxation times T₂ (${NV}^{-}$ center: 50 µs and $V_B^{-}$: 15 µs) are influenced by the local nuclear environment and spin diffusion while Rabi oscillation damping times depend on crystal size and the spatial distribution of microwave excitation. The ENDOR absorption width varies significantly among color centers due to differences in crystal structures. These findings underscore the importance of selecting an appropriate material platform for developing quantum registers based on high-spin color centers in quantum information systems. Full article

Phonon blockade is an important quantum effect for revealing the quantum behaviors of mechanical systems. For a nitrogen-vacancy center spin strongly coupled to a mechanical resonator via the second-order magnetic gradient, we show that the qubit driving can lead to the implementation of the two-phonon blockade, while the usual mechanical driving only allows for the appearance of a single-phonon blockade. As a signature, we investigate three-phonon antibunching with a simultaneous two-phonon bunching process by numerically calculating the second-order and third-order correlation functions. We also analyze in detail the influence of the system parameters (including the qubit driving strength, the dephasing rate of the qubit, as well as the thermal phonon number) on the quality of the two-phonon blockade effect. Our work provides an alternative method for extending the concept of a phonon blockade from a single phonon to multiphonon. It is of direct relevance for the engineering of multiphonon quantum coherent devices and thus has potential applications in quantum information processing. Full article