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. In order to be absolutely sure the atom was changing its magnetic state and this wasn't just some interference or effect from the STM's electric storm, the researchers set an iron atom down nearby. This atom is affected by its magnetic neighborhood, and acted differently when probed while the Holmium atom was in its different states. This proves that the experiment truly creates a lasting, stored magnetic state in a single atom that can be detected indirectly. And there you have it: a single atom used to store what amounts to a 0 or a 1. The experimenters made two of them and zapped them independently to form the four binary combinations (00,01,10,11) that two such nodes can form.