Enabling quantum sensing under extreme pressure: Nitrogen-vacancy magnetometry up to 130 GPa

Engineering a layer of nitrogen-vacancy (NV) centers on the tip of a diamond anvil creates a multipurpose quantum sensor array for high-pressure measurements, especially for probing the magnetic and superconducting properties of materials. Expanding this concept above 100 GPa appears to be a substantial challenge. We observe that deviatoric stress on the anvil tip sets a limit at 40--50 GPa for practical magnetic measurements based on the optically detected magnetic resonance (ODMR) of NV centers under pressure. We show that this limit can be circumvented up to at least 130 GPa by machining a micropillar on the anvil tip to create a quasihydrostatic stress environment for the NV centers. Improved hydrostaticity is quantified using the pressure dependence of the diamond Raman shift, the NV ODMR dependence on applied magnetic field, and NV photoluminescence spectral shift. This paves the way for the reliable use of NV microsensing at pressures above 100 GPa.