The limit for information density seemed to be set: at best, a bit could be stored in the presence, or absence, of an atom or electron. But Chris Moon and his colleagues at Stanford University in California have found a way to store data in subatomic spaces using quantum holograms.
They stuck carbon monoxide molecules on a thin layer of copper using a scanning tunnelling microscope. A pond of electrons 'illuminated' the arrangement of these gas molecules, and where extra information was stored in the probabilistic shape of an electron's quantum wave, that electron formed part of a hologram. Together, the data-rich electrons formed an 'S' — for Stanford — with a linewidth as small as 0.3 nanometres.