Titolo della tesi: Compact quantum sensing device with Nitrogen-Vacancy centers in diamond
The following work and the related experiments were carried out with the support and hospitality of the Department of Basic and Applied Science for Engineering of Sapienza University of Rome and the "Quantum Optics Lab" of Leonardo S.p.A., under the supervision of Professor Fabio Antonio Bovino, who provided me with the knowledge and tools necessary for the development of this thesis.
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 light-matter 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.