TheWeak Orthogonal Field regime in Nitrogen-Vacancy color centers in diamond for Quantum Sensing

In the area of Quantum Technologies, the use of a quantum system to detect a physical quantity led to the development of Quantum Sensing and Metrology, a field that focuses on the investigation of how couplings between a quantum system and its environment can be employed to measure a specific physical observable. Among the numerous amount of Quantum Sensors that have been studied, the Nitrogen-Vacancy center in diamond emerged as one of the most promising candidates due to the great number of different couplings that can be exploited and to its remarkable quantum properties at standard pressure and temperature conditions, leading to applications into wide variety of fields such as biology, medicine and aerospace. The different couplings between the spin-triplet ground state of the Nitrogen-Vacancy center and several physical quantities have been extensively studied and employed to measure temperature, magnetic fields, electric field and pressure down to nanometric spatial resolutions given by the atomic nature of the defect. However, decoupling the effects of multiple fields that interact simultaneously with the sensor can be challenging, since all fields can induce variation in eigenenergies and eigenstates of the NV ground state Hamiltonian. Nevertheless, these states can be used as a resource to improve the quantum properties of a NV-based sensor by applying controlled biases. The new eigenstates are, in general, superposition of the eigenstates of the system in absence of external fields. The work presented in this dissertation focuses on the investigation of the effects of weak fields applied orthogonally to the quantization axis of the Nitrogen- Vacancy center from an experimental and also theoretical level, with specific emphasis on the interplay between weak orthogonal magnetic fields and electric fields. In the theoretical section of this work the interplay between electric and magnetic weak orthogonal field is rigorously studied, by computing the exact solution for the final eigenstate NV electronic ground state when the two types of field have a similar strength, opening up new possibilities of improving the performance of NV based quantum sensor by tuning the orientation of bias fields with respect to the driving fields required to operate the sensor. Finally, in the experimental section of this work, V the coherence of the different states generated by the action of the aforementioned fields are measured and the improvement given by state superposition is evaluated, modeling accurately the different coherence properties of the generated eigenstate