Fabrication and Utilization of NV Flakes for High-Pressure Quantum Sensing above 1.5 Megabar

High-resolution quantum sensing under extreme conditions is essential for condensed matter physics. Nitrogen-vacancy (NV) centers enable in situ magnetic imaging inside a diamond anvil cell, yet current approaches rely on either randomly oriented particles or custom-fabricated diamond anvils─offering ease of integration or field imaging, respectively, but not both. Here we present NV flakes as a unified platform: micrometer- to submicrometer-thicksingle-crystal flakes characterized by optically detected magnetic resonance and photoluminescence. We clarify the origins of anomalous spectral features and demonstrate robust NV sensing above 1.5 megabar. Detecting the Meissner effect in a 100 nm YBCO film confirms the flakes’ promise for high-pressure quantum metrology.