Grassellino directs the DOE's SQMS Center, a Fermilab-Northwestern-led national quantum initiative center, and pioneered nitrogen-doping surface treatments that give niobium superconducting RF (SRF) cavities record-high quality factors. Beyond their traditional use in particle accelerators, these ultra-high-Q cavities are now deployed as extremely sensitive electromagnetic detectors: the Dark SRF experiment set new sensitivity limits on dark-photon light-shining-through-wall searches, and SRF cavities (e.g. the MAGO design) are being explored as high-frequency gravitational-wave and axion detectors, alongside long-lived multimode quantum memories for superconducting quantum computing.