  Resolving single atoms in large-scale volumes has been a goal for atomic
resolution microscopy for a long time. Electron microscopy has come close to
this goal using a combination of advanced electron optics and computational
imaging algorithms. However, atomic-resolution 3D imaging in volumes larger
than the depth of field limit of the electron optics has so far been out of
reach. Electron ptychography, a computational imaging method allowing to solve
the multiple-scattering problem from position- and momentum-resolved
measurements, provides the opportunity to surpass this limit. Here, we
experimentally demonstrate atomic resolution three-dimensional phase-contrast
imaging in a volume surpassing the depth of field limits using multi-slice
ptychographic electron tomography. We reconstruct tilt-series 4D-STEM
measurements of a Co3O4 nanocube, yielding 1.75 {\AA} resolution in a
reconstructed volume of (18.2nm)^3.
