Painter's group pioneers cavity- and phononic-crystal optomechanics for quantum-limited displacement and force sensing, ground-state cooling, phononic quantum circuits, and microwave-to-optical transduction linking superconducting qubits to optical photons. For context, this complements the established paradigm of NV-diamond ensemble magnetometry (Hahn-echo/DEER, nanoscale NMR, T1 relaxometry) operating near pT/√Hz sensitivity.