IBM has has now managed to read and write data to a single atom. This advance may be more symbolic than practical right now, but merely showing a working example of atomic data storage, orders of magnitude smaller than state of the art techniques, is practically science fiction.
It works like this: A single Holmium atom (a large one with many unpaired electrons) is set on a bed of magnesium oxide. In this configuration, the atom has what’s called magnetic bistability: It has two stable magnetic states with different spins (just go with it).
Because the two states have different conductivity profiles, the STM tip can detect which state the atom is in by applying a lower voltage (about 75 millivolts) and sensing its resistance.