We present a fiber-integrated hBN cavity enabling efficient optical readout of spin defects for remote, room-temperature quantum sensing of magnetic fields, offering robust, multifunctional capabilities for confined or remote environments across various applications.
Fiber-Integrated van der Waals Quantum Sensor The cover image illustrates a fiber-integrated van der Waals quantum sensor. The circular Bragg grating cavity fabricated from hexagonal boron nitride (hBN) with optically active spin defects, is integrated with an optical fiber using a deterministic transfer technique. The fiber-integrated hBN cavity enables efficient excitation and collection of signal without the need of a confocal microscope. The fiber-based quantum sensing platform may pave the way to a new generation of robust, remote, multi-functional quantum sensors. For further details, see article number 2401987 by Je-Hyung Kim, Igor Aharonovich, and co-workers.
Quantum sensing aims to detect signals with unparalleled sensitivity, potentially surpassing classical limitations. Solid-state spin defects, particularly nitrogen-vacancy centers in diamond, have emerged as promising platforms due to their long coherence time, optical addressability, high field sensitivity, and spatial and spectral resolution, making them ideal for sensing and imaging applications. Their compact size and robust performance under room temperature and ambient conditions further enhance their suitability for real-world applications. We provide an overview of quantum sensing principles and explore efforts to improve sensor functionality, including advanced sensing protocols, spatial imaging techniques, and integration with optical systems to enhance detection efficiency. We also highlight recent progress in the applications of these sensors across various use cases, including biomedical diagnostics, semiconductor device inspection, and industrial and military applications.
Negatively charged boron vacancy (VB−) centers in hexagonal boron nitride (h-BN) have attracted wide-range interests owing to their van der Waals lattice and their potentials for in-situ quantum sensing. Here we propose and experimentally demonstrate an all-optical strategy for wide-field magnetometry based on VB− centers. This strategy exploits the magnetically sensitive ground-state level anti-crossing (GSLAC) of VB− centers, which induces a strong electron spin transition between mS=0 and mS=−1 states, enabling microwave-free magnetic field measurement. By monitoring the shift of GSLAC feature, the external magnetic field can be precisely determined. Using this technique, we demonstrate all-optical wide-field imaging of near-field DC magnetic field distribution from current-carrying circuits over an area of around 42 × 21 μm2. An estimated photon shot-noise-limited sensitivity of 67.1 μT/Hz is achieved for a single pixel, which is an approximately threefold improvement over the ODMR method, along with a spatial resolution of about 1 μm per pixel. Our approach expands the applicability of VB− centers in quantum sensing, paving the way for robust and convenient magnetometry under extreme conditions.
Nanoscale thermometry and magnetometry are in high demand across a wide range of scientific and technological applications. In this context, optically addressable spins in solids have emerged at the forefront of on-chip quantum sensing. However, simultaneous quantum sensing of multiple parameters (e.g., temperature and magnetic field) using the same spin sensor remains challenging due to cross-sensitivity to multiple physical quantities. Here, we demonstrate independent dual sensing of temperature and magnetic field using single quantum emitters in hexagonal boron nitride (hBN). We experimentally verify the independent response of the zero-phonon line (ZPL) position to temperature and of optically detected magnetic resonance (ODMR) to magnetic fields. Furthermore, we demonstrate local temperature sensing of a microcircuit while simultaneously measuring an external magnetic field. Our results establish quantum emitters in hBN as a robust platform for multifunctional quantum sensing under realistic operating conditions.
Quantum sensing and metrology" is a relatively new research field.However, this research field is growing rapidly because of some outstanding features that pre-existing technologies do not have.We can thus achieve sensing with extremely high sensitivity across wide dynamic ranges, such as magnetic fields and temperature, or extremely accurate measurements of factors such as gravity, time, and position using quantum sensing and metrology.Multiple sensing of magnetic fields and temperature is also one of the attractive features of quantum sensing.In addition, the information with nanometer ranges extracted in local areas can be observed using nanoparticles with quantum sensors since only one spin defect can act as a sensor.These features for quantum sensing and metrology open new doors to a wide variety of fields and, as a result, ideas for new applications beyond our present imagination.Although groundbreaking demonstrations have been previously reported (Kucsko et al., 2013;Tetienne et al., 2017;Thiel et al., 2019), it is difficult to say that technology for quantum sensing and metrology is well developed at present.The quality of host materials for spin defects that act as quantum sensors should be improved.For example, diamond is a host material for the negatively charged nitrogen-vacancy (NV) center, which is one of the most famous spin defects that acts as a quantum sensor (Balasubramanian et al., 2008).At present, there is no technology to fabricate diamond wafers of large diameters.Besides, we must develop controlling methods for reducing crystal defects, including unintentionally doped impurities, although the quality of diamond substrates improves day by day.Of course, diamond is not only a host material for spin defects but also other materials, such as silicon carbide (SiC), Gallium nitride (GaN), and hexagonal boron nitride (hBN), are expected to be applied to host materials (Ohshima et al., 2018;Gottscholl et al., 2021;Hoang, 2022), and researchers are making a significant effort to improve the quality of such materials.New host materials for spin defects as well as new spin defects themselves will be found in the future and, as a result, the applications of quantum sensing will be expanded to cover a broad range of fields.In addition, it is important to establish methodologies for introducing spin defects in host materials.So far, two major methods are applied to the introduction of such spin defects during crystal growth and energetic particle irradiation (Balasubramanian et al., 2009;Yamamoto et al., 2013).Introducing spin defects during crystal growth has an advantage from the point of view of the quality of spin defects as well as host materials since unexpected residual defects that have a harmful impact on spin defects are also introduced by irradiation.For sensing with extremely high sensitivity, spin defects with