  We demonstrate super-resolution optical sensing of the size of the wave
packet of a single trapped ion. Our method is inspired by the well known ground
state depletion (GSD) technique. Here, we use a hollow beam to strongly
saturate a dipole-forbidden transition around a sub-diffraction limited area at
its center and observe state dependent fluorescence. By spatially scanning this
laser beam over a single trapped $^{40}\mathrm{Ca}^+$ ion, we are able to
distinguish the wave packet sizes of ions cooled to different temperatures.
Using a depletion beam waist of $4.2(1)\,\mu$m we reach a spatial resolution
which allows us to determine a wave packet size of $39(9)\,$nm for a near
ground state cooled ion. This value matches an independently deduced value of
$32(2)\,$nm, calculated from resolved sideband spectroscopy measurements.
Finally, we discuss the ultimate resolution limits of our adapted GSD imaging
technique in the view of applications to direct quantum wave packet imaging.
