AVS 71 Session QS2-TuM: Quantum Foundries, Educational Initiatives, Sensing and Metrology

The re-definition of the SI units enables new ways to realize fundamental units. Quantum-based metrology systems, however exciting, do raise new challenges and several important questions: Can these new realizations enable the size and scale of the realization to be miniaturized to the point where it can be imbedded into everyday products?What will be the role of metrology institutes in the is new ecosystem of metrology and measurement?This talk will begin to explore these important philosophical questions.The technical core of the talk will be a deeper dive into research on measurement methods for pressure, the Fixed Length Optical Cavity (FLOC) and for vacuum the Cold Atom Vacuum Standard (CAVS).What is exciting about many of these new measurement approaches is that they are both primary (relying on fundamental physics), are quantum-based and use photons for the measurement readout which is key for taking advantage of the fast-growing field of photonics.

We present radio frequency (RF) reflectometry measurements that have been combined into a millikelvin scanning tunneling microscope (mK-STM). This technique is realized through a relatively straight forward integration of an LC tank circuit into the STM tip-plate. For semi-conductor samples, application of a voltage bias gives rise to tip-induced band bending which leads to the formation of an induced quantum dot that can be scanned across the sample surface. This measurement geometry provides a unique detection method, as variations in the energy of a state confined to the tip-induced quantum dot due to the local environment leads small changes in quantum capacitance. These capacitance variations can be effectively sensed via RF reflectometry of the tunnel junction provided the tank circuit has a sufficient quality factor Q. In particular, we find strong phase contrast in the presence of resonant tunnel coupling between the induced dot and sub-surface defect states. As a demonstration of this capability, we present experimental results on highly phosphorus doped (10¹⁹cm^-3) Si(100). 1-D voltage dependent spectroscopy measurements in the vicinity of defects reveal ring-like structures in the reflected phase that can be effectively modeled by an asymmetric double-dot detuning picture. This technique ultimately aims to emulate read-out geometries relevant to modern quantum dot devices.