MEMS Measurement of Position-Depenent Phonon Collection in KIPMs

We employ a micro-electro-mechanical system (MEMS) mirror-based calibration system to probe open questions about kinetic inductance phonon-mediated (KIPM) detectors. These KIPM devices are superconducting resonators sensitive to phonons generated in the substrate. Similar aluminum KIPM devices have shown O(10eV) baseline sensitivity to the energy absorbed into the KIPM, but were found to have phonon collection efficiency below one percent. The low phonon collection efficiency limits the overall detector sensitivity. Using the MEMS-based calibration system to steer an LED onto different locations of the detector substrate, we investigate the underlying spatial dependence of the phonon collection efficiency in KIPMs. This approach can be used to understand phonon collection in various superconducting systems including superconducting qubits and dark matter detectors.