During the last decade, nitrogen-vacancy (NV) centers in diamond have gained a prominent role within the field of quantum technologies. These color defects inside the diamond lattice have been proved to be an extraordinary platform that assists in many of the current challenges that cutting-edge research is facing. The application of these novel tools exceeds the borders of quantum physics and reaches fields such as medicine, biology or chemistry. This thesis is focused on the development of novel theoretical schemes that intend to open new ways of understanding the NV centers as a quantum tool and sensor with direct applications. The manipulation of NV centers has become relatively easy in these last years. Moreover, via a proper control, the environment of an NV center may be overridden. In this thesis, we treat the NV center as a tool for enhancing the performance of nuclear magnetic resonance (NMR). Since the resolution of NMR is largely limited by the poor polarization of certain organic molecules, we here create and develop a theoretical frame that uses the NV center as a tool to transfer polarization toward organic samples in an efficient and controllable manner. In addition, this theoretical effort is supported by extensive numerical simulations and, moreover, all the predictions are confirmed by experimental evidence. Therefore, we demonstrate polarization transfer to external molecules at room-temperature paving the way for high-resolution NMR. Motivated by the success of the NV center as a polarization tool, we have further extended our analysis aiming to develop a phase transition sensor. In particular, we propose the NV center as a tool to assist current research on chemical reactions and molecular dynamics occurring at solid-liquid interfaces. These processes occur at a nanometric scale and thus, a nanometric sensor is desirable. In this context, the NV center is introduced as an ideal platform to investigate exotic phases of water when deposited onto diamond surface at room-temperature. In fact, recent studies predict that ultra-thin layers of water behave differently from bulk water due to interactions between water molecules and carbon atoms in the diamond surface. Through this thesis, we provide a theoretical and numerical work that predict how the NV center spin will behave in the presence of different phases of water, and hence, we reveal the NV center as a high-resolution sensor able to determine internal structures.
During the last decade, nitrogen-vacancy (NV) centers in diamond have gained a prominent role within the field of quantum technologies. These color defects inside the diamond lattice have been proved to be an extraordinary platform that assists in many of the current challenges that cutting-edge research is facing. The application of these novel tools exceeds the borders of quantum physics and reaches fields such as medicine, biology or chemistry. This thesis is focused on the development of novel theoretical schemes that intend to open new ways of understanding the NV centers as a quantum tool and sensor with direct applications. The manipulation of NV centers has become relatively easy in these last years. Moreover, via a proper control, the environment of an NV center may be overridden. In this thesis, we treat the NV center as a tool for enhancing the performance of nuclear magnetic resonance (NMR). Since the resolution of NMR is largely limited by the poor polarization of certain organic molecules, we here create and develop a theoretical frame that uses the NV center as a tool to transfer polarization toward organic samples in an efficient and controllable manner. In addition, this theoretical effort is supported by extensive numerical simulations and, moreover, all the predictions are confirmed by experimental evidence. Therefore, we demonstrate polarization transfer to external molecules at room-temperature paving the way for high-resolution NMR. Motivated by the success of the NV center as a polarization tool, we have further extended our analysis aiming to develop a phase transition sensor. In particular, we propose the NV center as a tool to assist current research on chemical reactions and molecular dynamics occurring at solid-liquid interfaces. These processes occur at a nanometric scale and thus, a nanometric sensor is desirable. In this context, the NV center is introduced as an ideal platform to investigate exotic phases of water when deposited onto diamond surface at room-temperature. In fact, recent studies predict that ultra-thin layers of water behave differently from bulk water due to interactions between water molecules and carbon atoms in the diamond surface. Through this thesis, we provide a theoretical and numerical work that predict how the NV center spin will behave in the presence of different phases of water, and hence, we reveal the NV center as a high-resolution sensor able to determine internal structures.
In recent years, defect centers in wide band gap semiconductors such as diamond, have received significant attention. Defects offer great utility as single photon emitters, nanoscale sensors, and quantum memories and registers for quantum computation. Critical to the utility of these defects, is their charge state. In this dissertation, experiments surrounding the charge state dynamics and the carrier dynamics are performed and analyzed. Extensive studies of the ionization and recombination processes of defects in diamond, specifically, the Nitrogen Vacancy (NV) center, have been performed. Diffusion of ionized charge carriers has been imaged indirectly through the recapture of said carriers by optically active defects such as the NV center and the Silicon Vacancy (SiV) center. With proper understanding of the carrier dynamics, diamond stands to be a strong competitor in the field of spintronics for quantum information processing. Additionally, the understanding of these charge state dynamics is utilized in a novel proof of principle experiment, showing that the NV center defect’s charge state could serve as an ultra-dense 3D memory platform. The NV center has also been used as a nanoscale magnetometer. The high degree of spin polarization and the ease of manipulation of the NV allows us to transfer this polarization to other spins in the diamond and assists in the detection of spins outside of the diamond. Ensembles of Nitrogen Vacancy centers can be used to perform NMR spectroscopy of sample volumes not achievable through traditional methods. The operating mechanisms of the magnetic resonance aspects of the NV center will be discussed in depth. Work surrounding the control and polarization of the NV center’s host nitrogen spin will be covered. The topic of sensitivity and methods to improve that sensitivity will be covered as well.
The Nitrogen-Vacancy (NV) color center is a defect of diamond which behaves as an artificial atom hosted in a solid-state matrix. Due to its electron spin properties which can be read-out and manipulated as an elementary quantum system, the NV center has found a wide panel of applications as a qubit for quantum information and as a magnetic field sensor. However these applications require to control the properties of the NV centers and their localization. This doctoral thesis investigates methods allowing us to tailor the properties of NV centers by combining techniques for the implantation of nitrogen atoms and the plasma-assisted (CVD) synthesis of diamond.The manuscript is divided into six chapters. The first chapter summarizes the properties of the NV center which will set our objectives for the NV engineering. The second chapter will describe how arrays of NV centers can be created using Focused Ion Beam implantation. The results open a wide range of applications for the targeted creation of NV centers in diamond structures such as photonic crystals and tips. However the low kinetic energy which is required for achieving implantation within a spot of 10-nm diameter leads to shallow defects which properties are strongly affected by the sample surface. The third chapter investigates how the overgrowth of a diamond layer over implanted NV centers can remove the detrimental influence of the surface. The fourth and fifth chapters describe effective methods for NV center fabrication through the control of the CVD growth conditions of the hosting crystal. Thin layers with high NV doping can be grown and almost perfect control of the orientation of the NV axis can be achieved. With the goal to optimize the spin coherence properties, the sixth chapter investigates how the electron spin of the NV center can be protected from decoherence effects induced by magnetic noise due to the unpolarized spins in the diamond lattice.
In recent years, the field of quantum sensing has garnered increasing attention due to its potential to revolutionize various scientific and technological domains. Among the different quantum sensors, the nitrogen-vacancy (NV) color center in diamond stands out for its ease of use, ability to be read out and initialized with a laser, and long coherence times even at room temperature. Over the past years, numerous quantum control sequences have been developed to successfully deploy NV sensors in diverse situations, such as measuring nearby spin clusters, classical AC signals, and static magnetic fields. However, the NV center faces limitations when coupling to high frequency signals. More specifically, as the frequency of the target signal increases, stronger driving fields over NVs are needed, ultimately reaching the limits of current experimental capabilities. In this thesis, we propose several protocols to address this high-frequency problem in different scenarios.
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.
This thesis investigates the theoretical foundations, material properties, and experimental realization of quantum sensors based on the Nitrogen-Vacancy (NV) centers in diamond, a solid-state system that combines quantum coherence with room-temperature operability. The first chapter introduces the principles of quantum sensing, outlining the fundamental definitions, operating protocols, and physical processes underlying the quantum measurement paradigm. Emphasis is placed on the quantum sensing Hamiltonian and the distinction between various classes of quantum sensors. The second chapter focuses on diamond as a host material and on the NV center as a quantum defect. The electronic structure, optical transitions, and spin properties of the NV center are analyzed in detail. Several techniques of NV-based magnetometry are presented, including continuouswave and pulsed optically detected magnetic resonance (ODMR). The discussion also addresses coherence times (T1, T2, and T∗2 ) and methods of diamond synthesis together with NV-center generation through irradiation and annealing. Chapter three develops the physical theory describing the NV center. The Hamiltonian formalism includes spin-spin, hyperfine, and quadrupolar interactions, as well as couplings to external magnetic fields. The chapter further introduces the Bloch sphere representation, magnetic resonance phenomena, and models of lightmatter interaction, ranging from the semiclassical to the fully quantum Rabi framework. A seven-level rate-equation model is proposed to capture the spin dynamics and optical cycling processes of the NV center. The fourth chapter reports the experimental results. After describing materials and methods, several ODMR-based vector magnetometry experiments are presented, highlighting different spectral regimes and the dependence of resonance features on the external magnetic field geometry. Additional studies demonstrate temperature sensing and microwave-free magnetometry techniques for mapping magnetic field distributions. Sensitivity analysis and calibration procedures are also discussed.
As a demand from developing nanotechnology and quantum information technology based on mesoscopic material, quantum sensors with better spatial resolution and sensitivity are required. \n \nHowever, few material meets the requirements of nanoscale sensors including stability and small size. Single spin of Nitrogen-Vacancy(NV) centers in diamond crystal is one kind of the ideal quantum sensors for magnetometry that has been investigated in recent years. It provides a potential way to study the dynamics in a mesoscopic system with high sensitivity at room temperature. This thesis proposes a theoretical method to realize spin interaction detection based on NV centers on an atomic force-microscopy(AFM) tip. To realize this method, a robust control on NV centers and target electron spins at zero magnetic field is necessary. A pulse control technique for NV centers is proposed to realize transitions between two degenerate states at zero magnetic field, which is an important part of the sensing method. The key to realizing this transition is a circularly polarized microwave pulse generated by two parallel wires. Combined with optimal control techniques, this pulse can achieve a gate fidelity over 99.95% theoretically.