Albert Schliesser's group engineers ultracoherent phononic crystal membrane resonators with dissipation-dilution Q>10^9 and uses them for quantum optomechanics: ground-state cooling, back-action-evading measurement, optical quantum memory for single photons, and microwave-optical quantum transduction. Recent work has demonstrated a soft-clamped topological phononic waveguide (Nature 2025) and scanning force microscopy below the standard quantum limit. The group bridges fundamental quantum physics with novel sensors for electromagnetic fields and forces, and mechanical interfaces for hybrid quantum networks.