Fruth is an experimentalist on LZ, the world-leading liquid-xenon dark matter experiment, and works on the detector-physics end: electron and single-photon backgrounds, calibration, and the characterisation of the anomalous low-energy events that currently limit sensitivity at the bottom of the energy spectrum. The programme is a pure exercise in pushing a detector's noise floor down until it is limited by irreducible physics (the neutrino fog). Positioned against the established body of NV-ensemble quantum sensing work — DEER, nanoscale NMR and T1 relaxometry protocols operating at pT/sqrt(Hz) field sensitivity — dark matter detection and NV-ensemble magnetometry are the same problem in different clothing — an exquisitely quiet detector, a signal below the background, and a systematics budget that determines everything — and the quantum-sensing community is increasingly supplying the readout technology (quantum-limited amplifiers, single-photon counters) that these experiments now need. Early-career PI.

Works on quantum-limited sensing for astroparticle physics. Directions: (1) Pierre Auger Observatory — UHE cosmic ray composition and spectrum via radio and fluorescence detection; (2) liquid argon dark matter detectors; (3) co-PI DARPA QuSeN (2025) — quantum sensing of neutrinos using phonon-coupled SC qubit sensors with Cleland and Chou. KICP member.

Builds radio and mm-wave quantum-limited sensing instruments for high-energy astrophysics and cosmology. Directions: (1) PUEO — balloon-borne radio Cherenkov (Askaryan) detector for ultra-high-energy cosmogenic neutrinos; (2) RNO-G — ground-based radio neutrino array at Summit Station, Greenland; (3) UHE cosmic ray radio detection methodology; (4) CMB instrumentation (BICEP/Keck, SPT, CMB-S4). 2025 APS Fellow; 2022 Moore EPII award. Director KICP.