High Pressure Quantum Sensing

Pressure alters the physical, chemical and electronic properties of matter. By compressing a material between two opposing brilliant cut diamonds, the diamond anvil cell enables tabletop experiments to reach pressures more than a million times that of atmospheric pressure. Since its development over half a century ago, it has enabled experiments to directly access pressure as a thermodynamic tuning parameter and has had a dramatic impact on quantum science, chemistry and materials physics. Among these impacts, a tremendous amount of recent attention has focused on the discovery of superconductivity in a class of hydrogen-based materials. When compressed to megabar pressures, these so-called super-hydrides are believed to exhibit the highest known critical temperatures, and have led to a nascent field that is equal parts exciting and controversial. Part of this controversy stems from the nature of the tool itself: especially at high pressures, it is tremendously challenging to extract local information from within a diamond anvil cell. 
In this Colloquium, I will describe a new approach to directly "see" the physics inside the science chamber of a diamond anvil cell at ultra-high pressures. The basic idea is deceptively simple: We directly integrate a thin layer of sensors into the surface of the diamond anvil that is actually applying the pressure. I will demonstrate the ability to perform diffraction-limited imaging of both stress fields and magnetism, with the latter allowing us to image the magnetic field expulsion associated with superconductivity. Applying our techniques to cerium hydride, we observe the dual signatures of superconductivity: diamagnetism characteristic of the Meissner effect and a sharp drop of the resistance to near zero. By locally mapping both the diamagnetic response and flux trapping, we directly image the geometry of superconducting regions, showing marked inhomogeneities at the micron scale.