Until we can manipulate the sub-atomic world, the ultimate computer memory chip would use individual atoms to store a single bit of information. Such an atom-based circuit would mark the final iteration of Moore's Law that suggests an anticipated doubling of devices density on a circuit every 18 months or so. Current magnetic storage technology relies on a million atoms per bit, but now Andreas Heinrich formerly of IBM Almaden Research Center, USA, and his team have used scanning tunneling microscopy to switch a single holmium atom, magnetically stabilized on a magnesium oxide surface, from 0 to 1 and back again, thus demonstrating the ultimate miniaturization of computer memory. Their demonstration might now pave the way to storage for a quantum computer.

Heinrich's team has a unique quantum sensor based on an iron atom that allows them to read the memory state of the holmium atom in this tiny device. They could also use tunnel magnetoresistance to show that the holmium state is sustained for several hours. Their work shows that even if a second holmium atom is present just one nanometer away from the original the two do not interfere with each other's quantum state and so can retain their memory. This is a surprising discovery, as one might assume that such proximity would lead to one atom wiping the memory state of the other. With this discovery, the team could build a two-bit device with four possible distinct memory configurations, 1-1, 0-0, 1-0 and 0-1, seen by the iron sensor. [FD Natterer et al. Nature (2017); DOI: 10.1038/nature21371]

An end to Moore's Law has been predicted for many years, perhaps even from its initial formulation in the 1960s by the co-founder of Fairchild Semiconductor and Intel, Gordon Moore. Fabrication techniques were initially seen as the limiting factor even if the shorter wavelength of ultraviolet and perhaps even X-rays might be amenable to masking and etching components in silicon at ever-smaller scale. But, the final point would theoretically be the single atom device. However, it was always assumed that this would be off-limits because quantum interference would arise between individual atoms. Now, Heinrich's team has shown that this might not be the hindrance once predicted. Indeed, holmium atoms seem to evade the interference issue, although the team cannot yet explain this. "There are no quantum mechanical effects between atoms of holmium," Heinrich says. "Now we want to know why." The team explains that holmium atoms can be packed tightly together, so the storage density of a device based on this single-atom will be about one thousand times higher than any magnetic hard drive."We have opened up new possibilities for quantum nanoscience by controlling individual atoms precisely as we want," Heinrich adds. "This research may spur innovation in commercial storage media that will expand the possibilities of miniaturizing data storage."

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".