A recent theoretical study has explored the conversion of gravitons into phonons within resonant bar detectors, a phenomenon that could be crucial for the detection of single gravitons. First-order perturbation theory predicts a strong enhancement of this conversion for coherent and squeezed graviton states. However, this approximation can lead to conversion probabilities exceeding unity for large coherence or squeezing parameters, which violates unitarity.

To address this limitation, researchers exactly solved the graviton-phonon quantum dynamics using the rotating-wave approximation. The results reveal unexpected behavior: for an initial coherent graviton state, the conversion to phonons is not continuous but occurs intermittently. Narrow bursts of conversion are observed, separated by intervals of strong suppression. This intermittency pattern is a distinctive feature of non-perturbative quantum dynamics.

In the case of an initial squeezed state, the departure from perturbative behavior occurs even earlier. After its initial growth, the conversion is strongly suppressed. These effects of intermittency and suppression, not predicted by perturbation theory, could provide unique signatures of quantum graviton-phonon dynamics. Their understanding is fundamental for the design and interpretation of future experiments aimed at graviton detection, opening new avenues to explore the quantum nature of gravity.