Hyperpolarization and sensing with color centers in diamond

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