The existence of superionic ice has been confirmed in previous experiments, which holds significant implications for building accurate model and understanding evolutionary processes of ice giant planets. However, the proton diffusion mechanism in such systems, where a solid oxygen lattice coexists with freely diffusive protons, remains poorly understood. Here, by combining machine learning with path-integral molecular dynamics simulations, we uncover the quantum dynamical mechanism of proton diffusion in ice VII and VII''. Even at high temperature and pressure, nuclear quantum effects remain significant and lead to an increase in the critical temperature of superionic transition. This arises from the interplay between cooperative and cage effects, where nuclear quantum effects cause the latter one to dominate over the former one. Our work provides fundamental microscopic insights into the dynamic nature of superionic systems.

superionic ice,proton diffusion,nuclear quantum effect,path integral molecular dynamics