The diamond NV center is expected to be applied to high-sensitivity quantum magnetic sensors. The excellent spin characteristics are derived from the physical properties of diamond as a high-temperature material, and it has already been reported that the spin coherence time at room temperature exceeds 2 ms. In order to improve the sensitivity, it is indispensable to improve the crystalline quality and appropriately form the NV centers. In this talk, we will focus on the research conducted at NIMS regarding diamond crystal growth for the purpose of quantum magnetic sensor application.
The diamond NV center is expected to be applied to high-sensitivity quantum magnetic sensors. The excellent spin characteristics are derived from the physical properties of diamond as a high-temperature material, and it has already been reported that the spin coherence time at room temperature exceeds 2 ms. In order to improve the sensitivity, it is indispensable to improve the crystalline quality and appropriately form the NV centers. In this talk, we will focus on the research conducted at NIMS regarding diamond crystal growth for the purpose of quantum magnetic sensor application.
Quantum sensors utilize quantized energy levels, quan- tum superposition states, and eventually quantum entan- glement, which are also key elements in quantum comput- ing. Electronic and nuclear spins in semiconductors may serve as quantum sensing elements or qubits. The phos- phorus donor in silicon is an ideal qubit in terms of coherence time because of highest chemical purity of host material with isotopic 28Si enrichment and a very low den- sity of structural defects. However, it requires a cryogenic temperature to avoid ionization of the donor. In contrast in diamond, due to the wide band gap, the nitrogen-vacancy (NV) center exhibits optical initialization and readout of its spin state and a long coherence time even above room temperature, promoting its research and development as quantum sensors or qubits. Nevertheless, the syn- thesized diamond crystals with NV centers are not so per- fect as silicon. Therefore, the host material characteriza- tion is essential to improve the bulk-ensemble sensi- tivity to the magnetic field. The present study shows how to measure the spin properties of the diamond as a sens- ing host via the NV centers themselves and how to utilize such information to improve the sensor performance.
The physical properties of diamond crystals, such as color or electrical conductivity, can be controlled via impurities.In particular, when doped with nitrogen and under certain conditions, optically active nitrogen-vacany centers (NV) can be induced.The center is an outstanding quantum spin system that enables, under ambient conditions, optical initialization, readout, and coherent microwave control with applications in sensing and quantum information.Under optical and radio frequency excitation, the Zeeman splitting of the degenerate states allows the quantitative measurement of external magnetic fields with high sensitivity.This study provides a pedagogical introduction to the properties of the NV centers as well as a step-by-step process to develop and test, a simple magnetic quantum sensor based on color centers with large potential for the development of highly compact multi-sensor systems.
In modern-day quantum metrology, quantum sensors are widely employed to detect weak magnetic fields or nanoscale signals. Quantum devices, exploiting quantum coherence, are inevitably connected to physical constants and can achieve accuracy, repeatability, and precision approaching fundamental limits. As a result, these sensors have shown utility in a wide range of research domains spanning both science and technology. A rapidly emerging quantum sensing platform employs atomic-scale defects in crystals. In particular, magnetometry using nitrogen-vacancy (NV) color centers in diamond has garnered increasing interest. NV systems possess a combination of remarkable properties, optical addressability, long coherence times, and biocompatibility. Sensors based on NV centers excel in spatial resolution and magnetic sensitivity. These diamond-based sensors promise comparable combination of high spatial resolution and magnetic sensitivity without cryogenic operation. The above properties of NV magnetometers promise increasingly integrated quantum measurement technology, as a result, they have been extensively developed with various protocols and find use in numerous applications spanning materials characterization, nuclear magnetic resonance (NMR), condensed matter physics, paleomagnetism, neuroscience and living systems biology, and industrial vector magnetometry. In this chapter, NV centers are explored for magnetic sensing in a number of contexts. In general, we introduce novel regimes for magnetic-field probes with NV ensembles. Specifically, NV centers are developed for sensitive magnetometers for applications where microwaves (MWs) are prohibitively invasive and operations need to be carried out under zero ambient magnetic field. The primary goal of our discussion is to improve the utility of these NV center-based magnetometers.
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
When the word diamond comes up, the majority of people thinks about engagement rings or gemstones. In fact, it is additionally, one of the most promising host materials for the implementation of advanced technology, exploiting the nature of quantum physics. Such quantum technologies have disruptive potential, ones the quantum effects can be applied in macroscopic, commercial products. The nitrogen-vacancy (NV) centre in diamond is a promising candidate to perform such tasks in the fields of quantum computation, quantum cryptography or metrology. Especially in the field of quantum sensing, the NV sensor impresses with nano-scale spatial resolution paired with high sensitivity. The electronic spin of the atomic-sized point defect can be initialised, manipulated and read-out at ambient conditions and coherence lifetimes are comparably long. Diamond magnetometers based on negatively charged NV centres have shown to be very attractive, and the sensitivity goes down to the single-atom level. In order to exploit such a high sensitivity level for sensing prospects, in this thesis, the NV centres are fabricated well confined in a certain distance to the diamond surface, since the detectable field usually decays with the third power of the distance between sensor and target. The surface depicts a fracture of the spin wise protecting diamond lattice and charge fluctuations affect the stability of NV centres, which are overcome by diamond surface termination. In order to improve the sensitivity further, the sensor density, measurement contrast and interaction time are increased. The nitrogen doping technique, which is applied during a plasma-enhanced chemical vapour deposition (PECVD) diamond growth process is used to fabricate NV centre ensembles aligned along one diamond crystal axis, thereby improving the measurement contrast by a factor up to four. The interaction time limiting spin bath is analysed using the sensor capabilities of the NVs, which leads to enhanced growth strategies and the fabrication of sensitivity optimised NV centre ensembles for magnetometry applications.