Using nitrogen-vacancy center diamond as a quantum sensor for magnetic anomaly detection

Abstract

The application of nitrogen-vacancy (NV) centers in diamond as a quantum-based technique for magnetic anomaly detection is examined in this thesis. Because of their exceptional quantum characteristics, NV centers can detect magnetic fields at room temperature. Because of their stable solid-state structure, high-resolution measurements can be made without the use of cryogenic equipment. The motivation behind this work comes from practical challenges in fields such as defense, geophysics, and biomedical sensing where detecting weak or hidden magnetic signals is crucial. Traditional magnetometers, such as SQUIDs or optically pumped systems (OPM) are sensitive but often require complex infrastructure. In contrast, NV-based sensors offer a more compact and portable solution, which was a key consideration in this study. In this work, we combined both theoretical concepts and hands-on lab experiments to explore the behavior of NV centers. The theoretical part covers how NV centers respond to external magnetic fields through the principles of zero-field splitting and the Zeeman effect. These physical topics form the foundation of the optically detected magnetic resonance (ODMR) technique, which is central to this study. On the experimental side, a complete NV magnetometry system was developed. It includes a green DPSS laser for excitation, optics to gather fluorescence from the diamond, and microwave components for spin manipulation. Lock-in amplification and digital filters were integrated into setup to reduce noise and improve signal clarity. Comparisons between two diamond samples: one is form a local company, Appsilon, and the other from Element Six to investigate how much material quality affects performance. During the experiments, we have come across several challenges that are not mentioned in the literature. Some of them include maintaining a stable laser in terms of both physical and temperature conditions. Also another challenge was integrating new component to the experimental setup, as it would require recalibration of each optical elements and sometimes the measurement devices. Even supplying a sufficient power to each component is requiring various methods. In addition, Choosing the lock-in amplifier detection method over previous ODMR methods comes with a great number of new considerations such as compactness and system robustness. Both static and adjustable magnetic fields were applied using permanent magnets and Helmholtz coils. Measurements were validated with a fluxgate magnetometer. ODMR spectra under various conditions helped to observe the system's response and also verify its sensitivity. One of the notable contributions of this study is focused on real-world applications, particularly in defense. We aimed to make the system as compact and adaptable as possible, especially considering future defense-related field uses with potential use cases including GPS-independent navigation and underwater vehicle detection. The work also opens possibilities for integrating NV-based sensors into other platforms, such as drones or mobile vehicles. In conclusion, this research demonstrates how NV diamond magnetometers can be developed from theory into functional magnetometers. While there are still technical challenges in terms of system stability, the potential applications are still worth working in this area. Future work could explore pulsed ODMR techniques, vector field depended magnetic sensing, and also single-NV applications for nanoscale precision.