  Thermal ripples of graphene are well understood at room temperature, but
their quantum counterparts at low temperatures are still in need of a realistic
quantitative description. Here we present atomistic path-integral Monte Carlo
simulations of freestanding graphene, which show upon cooling a striking
classical-quantum evolution of height and angular fluctuations. The crossover
takes place at ever-decreasing temperatures for ever-increasing wavelengths so
that a completely quantum regime is never attained. Zero-temperature quantum
graphene is flatter and smoother than classical at large scales, yet rougher at
short scales. The angular fluctuation distribution of the normals can be
quantitatively described by coexistence of two Gaussians, one classical
strongly T-dependent and one quantum about $2^{\circ}$ wide, of zero-point
character. The quantum evolution of ripple-induced height and angular spread
should be observable in electron diffraction in graphene and other
two-dimensional materials like MoS$_2$, bilayer graphene, boron nitride, etc.
