The Negatively-charged nitrogen vacancy center has emerged as a versatile quantum sensor in last decades. The contactless optical excitation and readout make it compatible with other condensed matter system. Moreover, the long-coherence spin properties has provided an excellent platform for performing quantum computation, using the spin state sub-levels as qubits. Diamond is a robust material with giant covalent structure, rendering it both chemically and physically stable. Being a diamond-based sensor has a key advantage over other solid defects, which is the resilience against extreme condition such as high-pressure, high-temperature and low-temperature while sensitive to external conditions like electric field, magnetic field and strain field. In addition, the defect center in atomic...[ Read more ]

The Negatively-charged nitrogen vacancy center has emerged as a versatile quantum sensor in last decades. The contactless optical excitation and readout make it compatible with other condensed matter system. Moreover, the long-coherence spin properties has provided an excellent platform for performing quantum computation, using the spin state sub-levels as qubits. Diamond is a robust material with giant covalent structure, rendering it both chemically and physically stable. Being a diamond-based sensor has a key advantage over other solid defects, which is the resilience against extreme condition such as high-pressure, high-temperature and low-temperature while sensitive to external conditions like electric field, magnetic field and strain field. In addition, the defect center in atomic scale facilitates local measurement, giving a high spatial resolution measurement. In light of this, we combine the high-pressure compatibility and the magnetic field sensitivity of NV center to probe superconductivity. The response of superconductivity to pressure can give us valuable insight into the mechanism of superconductivity behind some systems with strong electron-phonon coupling. Therefore, in this thesis we look into a high-temperature cuprate superconductor, YBa₂Cu₄O₈ (YBCO), to demonstrate the ability of NV center to unveil the physics contain in these hybrid system.