Exploring the Potential of Germanium Quantum Sensors for Probing High-Frequency Gravitational Waves

We present a simulation-driven assessment of high-purity germanium (Ge) quantum sensors targeted at ultra-weak, coherent excitations with an emphasis on prospective coupling to high-frequency gravitational waves (HFGWs). The GeQuLEP architecture—combining engineered Si/Ge heterostructures, high-Q phononic cavities, and hole-spin states read out via RF quantum point contacts—enables phonon–charge hybridization at cryogenic temperatures. Self-consistent Poisson–Schrödinger modeling, coupled to elastic-eigenmode analyses, yields localized hole states with strong spin–orbit interactions and long-lived phonon modes, establishing sub-eV strain sensitivity in the relevant GHz–THz window. We compute strain–phonon participation factors and mode-resolved coupling coefficients by projecting the gravitational-wave strain tensor onto quantized Ge lattice modes, and we identify resonance conditions where cavity dispersion and device geometry maximize signal transduction to charge. Performance projections map the achievable signal-to-noise to three experimentally actionable levers—phonon Q, mode volume/strain concentration, and readout noise temperature and delineate integration times required for quantum-limited detection. While the inferred GW–phonon coupling remains intrinsically weak, the results outline a realistic path to testable prototypes that leverage resonant enhancement, low thermal occupancy, and multiplexed readout. More broadly, this framework extends Ge-based qubit and phononics technology beyond computation toward fundamental detection science, providing concrete design targets for bridging condensed-matter quantum platforms with next-generation HFGW searches.