Currently it takes about a million atoms to store a bit on a modern hard-disk, the researchers from IBM say.
They believe this is the world's smallest magnetic memory bit.
According to the researchers, the technique opens up the possibility of producing much denser forms of magnetic computer memory than today's hard disk drives and solid state memory chips.
"Roughly every two years hard drives become denser," research lead author Sebastian Loth told the BBC.
"The obvious question to ask is how long can we keep going. And the fundamental physical limit is the world of atoms.
"The approach that we used is to jump to the very end, check if we can store information in one atom, and if not one atom, how many do we need?" he said.
Below 12 atoms the researchers found that the bits randomly lost information, owing to quantum effects.
A bit can have a value of 0 or 1 and is the most basic form of information in computation.
"We kept building larger structures until we emerged out of the quantum mechanical into the classical data storage regime and we reached this limit at 12 atoms."