We present a germanium phonon-to-charge transducer that integrates a slow-phonon phononic-crystal (PnC) region with radio-frequency quantum point-contact (RF-QPC) readout at 4 K, and we evaluate its dark-sector reach. A calibrated signal-collection model, which combines geometric guiding, propagation survival, and multiplicity-assisted primary-phonon detection, provides selection-corrected thresholds in the 10−3-10−2~eV range and a background model informed by nanosecond timing gates and GHz-band power-spectral-density windows. Under standard halo assumptions, a 100 g module achieves projected sensitivity to DM-electron and DM-nucleon scattering at recoil energies below 10−2~eV, probing cross sections below 10−43cm2 for mχ∈[0.01,100]MeV/c2 (with efficiencies and thresholds folded in). We present sensitivities for both heavy-mediator (FDM=1) and light-mediator (FDM∝1/q2) benchmarks, quantify dominant systematics (threshold, phonon quality factor Q, and bulk defect densities), and outline a staged program toward kg⋅yr exposures that begins to test models approaching the solar CEνNS background.
@article{arxiv.2511.08329,
title = {Probing low-mass dark matter from sub-MeV to sub-GeV with germanium-based quantum phononic spectroscopy},
author = {D. -M. Mei and N. Budhathoki and S. A. Panamaldeniya and K. -M. Dong and S. Bhattarai and A. Warren and A. Prem and S. Chhetri},
journal= {arXiv preprint arXiv:2511.08329},
year = {2025}
}