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
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
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.
The recent decade has witnessed exciting developments in quantum science and technology. Quantum sensing is a rapidly growing branch, which exploits the fragility of quantum systems to detect small external signals. The extreme control at the single-atom level and the remarkably long coherence time of engineered quantum systems enable unprecedented sensitivity and precision, beating the performance of classical techniques. The nitrogen-vacancy (NV) center in diamond is one of the most promising quantum sensors. Its unique advantages have attracted considerable attention, including a long spin coherence time throughout a broad temperature range, nanoscale resolution limited by the sensor-sample distance, convenient optical control of its spin states and remarkably versatile sensing capabilities. Its properties are well studied under a bias magnetic field oriented along its quantization axis. However, its sensing capabilities in the presence of an off-axis magnetic field are much less explored. My research aims to unlock the full potential of NV quantum sensor by developing new sensing modalities under a magnetic field acting perpendicular to the NV axis, and furthermore, integrating them into a scanning probe microscope. In this dissertation, I will report our progress toward building a scanning NV multimodal quantum imaging platform, which will open up exciting opportunities in measuring nanoscale phenomena. The first chapter provides an introduction to the background of quantum sensing with NV centers, followed by a discussion on its basic properties and established sensing techniques. The second and third chapters are dedicated to two experiments performed under a perpendicular magnetic field where traditional NV magnetometry based on the Zeeman effect fails. In the second chapter, I will introduce a new sensing strategy that uses the entanglement between the electron and nuclear spins to restore the magnetic field sensitivity under this unfavored condition. This allows us to sense small changes in the magnetic field angle relative to the NV axis, and to detect anisotropic magnetic noise in the local environment. In the third chapter, I will present our latest development of scanning NV electrometry, where a single NV at the apex of a diamond scanning probe images external alternating (AC) and direct (DC) electric fields with sub-100 nm resolution. In the last chapter, I will discuss our efforts on four experiments that were left unfinished. I will present the results we have achieved, analyze the challenges that we faced and propose potential solutions to overcome them.
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.
Atomic scale defects in diamond are emerging as next-generation quantum sensors. One such defect is the nitrogen vacancy (NV) center which possesses artificial atom-like properties making it a strong contender for a room temperature solid state qubit. These spin defects are optically addressable by studying their optically detected magnetic resonance spectra (ODMR). The spin states can be initialized, controlled, and read out by a shining laser. The photoluminescence spectra contain information on the external magnetic field, electric field, temperature, etc. Thus, this type of multimodal sensor is exigent in various fields of research viz. chemistry, materials science, biology, and fundamental physics. In today's world where energy-related products are booming, deployment of quantum sensors can expedite the development. Based on existing works, this paper makes an attempt to identify the applications of color centers in diamond for energy sectors. We have highlighted the efficacy of quantum diamond sensors in the oil and gas industry, battery research, and photovoltaics. In addition, a summary of the structural and quantum properties of defects in diamond, synthesis of diamond, protocols for optical detection of spin states, different types of color centers, etc., is presented.
Many quantum technologies are dual-use technologies that can introduce new capabilities to defence and security-related applications or increase their effectiveness. In particular, diamond-based quantum sensors have great potential due to the high robustness of this material in conjunction with quantum effects accessible at room temperature. The negatively charged nitrogen vacancy centre (NV-), an atomic defect within the diamond matrix, carries an electron spin that can be actively addressed and read-out via optical and electrical means at room temperature. This electron spin is highly sensitive to external magnetic fields, temperature, and pressure and thus well-suited for quantum sensing in defence and security. Nowadays, diamond is reliably produced by means of chemical vapour deposition, allowing for tailored sensor elements, such as with oriented NV centres in layers and in microstructures that are highly interesting for vector magnetometry. Sensitive magnetometry is useful in global magnetic navigation, detecting metallic objects like submarines, human-machine interfaces and more. Apart from that, radiofrequency signals are detected in real-time with GHz spectral coverage in radar analysis. Recently, the use of these diamond-based quantum sensing technologies for side-channel attacks has come into focus, for example, to gather information on implementation of algorithms for cryptosystems. These technologies are introduced along with the fabrication of the underlying diamond sensor element.
Quantum sensors encompass a diverse class of devices that exploit quantum coherence to detect weak or nanoscale signals. As their behavior is tied to physical constants, quantum sensors can achieve accuracy, repeatability, and precision approaching fundamental limits [1, 2]. As a result, these sensors have shown utility in a wide range of applications in both science and engineering leading to innovations. Among many solid-state spin systems, nitrogen-vacancy (NV) centers in diamonds have attracted considerable attention as a leading platform in many fields of quantum technologies, from quantum sensing to information processing and communication applications. They have superior physical properties, and their quantum coherence is preserved even at room temperature. The energy levels of NV centers are sensitive to magnetic fields, electric fields, strain, and temperature, and the spatial resolution is scalable from nanometers to millimeters. Therefore, diamond quantum sensors are distinctive sensors with multimodality and span scalable application fields. To realize an ideal quantum sensor for applications, the technical challenges in the sensor materials and the quantum control techniques, such as coherent microwave spin manipulation, effective optical spin-state initialization, and readout, have been developed. This chapter briefly explains the sensing principle using NV centers and then introduces sensor systems for biomedical applications, and monitoring of batteries for electric vehicles and internal power devices.