The study investigates the interaction between gravitational waves and massive quantum acoustic resonators (bar resonators) cooled to their quantum ground state. It is a theoretical analysis; no human or animal subjects are involved, and no sample size in terms of participants is applicable.

The work is a theoretical study proposing a detection scheme, involving analytical derivations and feasibility estimates; it is not an experimental study but a theoretical proposal.

No conflicts of interest are declared in the article; acknowledgements list funding sources but no competing interests are stated.

Key findings include derivation of spontaneous and stimulated single-graviton absorption/emission rates. Spontaneous emission rates are extremely low (e.g., ~10^{-40} Hz for atomic transitions) and thus unobservable. However, stimulated absorption rates can be significant: for an aluminum bar of mass ~1800 kg and gravitational wave amplitude h ≈ 5×10^{-22}, the stimulated transition rate Γ_stim ≈ 1 Hz. For a neutron star merger like GW170817, a beryllium resonator of mass ~15 kg at ~100 Hz could detect single gravitons. At higher frequencies (e.g., 5.5 MHz, h₀ ~10^{-16}), a resonator mass as low as ~10 g could suffice. The proposal relies on continuous quantum sensing of energy eigenstates and correlation with classical LIGO detections to identify single graviton absorption events.