Title: Diamond-Based Quantum Sensing for High-Pressure Superconductivity

Pressure is a key parameter in condensed matter to modify chemical bounds and material structure. Pressure also enhances the quantum properties that arise from electronic interactions, such as superconductivity. The workhorse of high-pressure investigations in condensed matter physics is the diamond anvil cell (DAC) where the pressurized sample is confined inside a drilled metallic gasket squeezed by two opposing diamond anvils. However, the confinement of the sample in the tiny dimension of the diamond anvil cell makes the implementation of any non-optical sensing technique both highly challenging and hardly reproducible.

 

Over the last years, we developed integrated quantum sensing systems that perform in situ measurements of quantum materials in a pressurized diamond anvil cell. This is realized by engineering a thin layer of optically active spin defects centers directly into the tip of a diamond anvil. Our choice is the nitrogen-vacancy (NV) color center that can be fabricated by nitrogen implantation using a focused ion beam that we specifically developed for this task. Using the magnetic field sensitivity of the NV center layer, we directly observed the Meissner effect associated to high-pressure superconducting materials such as a mercury-doped cuprate. Most importantly, we demonstrated that the NV center’s sensing efficiency remains robust up to megabar, i.e. hundred of gigapascals equivalent to a million of atmospheres. that the stress applied to the point defect remains hydrostatic in order to preserve its symmetry inside the diamond lattice that determines the quantum eigenstates on which the sensing capabilities are based.