Speaker
Description
There are growing efforts to use substrate-coupled kinetic inductance detectors as athermal phonon detectors for particle detection. One challenge encountered is the significant position-dependence these detectors can exhibit, destroying energy resolution of non-collimated sources. We show this position dependence can be overcome by operating the detectors to be sensitive to thermalized phonons. By thermally isolating the substrate from the housing, operating at above 100 mK, and utilizing pulse-shape information, we can reconstruct clear energy spectra from uncollimated gamma and alpha radiation sources. The uniform position-independent response of the MKIDs indicates efficient quasiparticle production far from the interaction site and implies that thermal excitations could cause chip-wide correlated errors in superconducting qubits.