https://techcrunch.com/2017/03/08/storing-data-in-a-single-atom-proved-possible-by-ibm-researchers/
Atoms, it may not surprise you to hear, are pretty much the smallest unit of matter that we can manipulate reliably and expect to stay still. There are interesting experiments with entangling photons, but they’re squirrelly customers. Better to stick to things that don’t fire off at the speed of light if you lose your grip for a second. And a previous atomic storage technique doesn’t actually store data in the atom, but moves them around to form readable patterns (still cool).
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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).
The researchers use a scanning tunneling microscope (also invented at IBM, in the 1980s) to apply about 150 millivolts at 10 microamps to the atom — it doesn’t sound like a lot, but at that scale, it’s like a lightning strike. This huge influx of electrons causes the Holmium atom to switch its magnetic spin state. 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.