https://www.youtube.com/watch?v=zqyZ9bFl_qg
I'd hate to go through the whole history of nanotechnology here; but, they've been trying to figure out to make this happen at least since the late 1970s. They've thought of many "enabling technologies", from STM's (scanning tunneling microscopes; a genuince quantum technology; it can image single atoms by means of quantum tunneling of electons. In quantum mechanics, there's Heisenberg's Uncertainty principle. Particles can tunnel from side of an energy barrier to another. Most of these only occur within the width of an atom. STM's actually detect electrons doing this), electron microscopes( Electrons microscopes as 3d printers have made pretty good progress lately as well. But, what I'm going to show is that STM's have come roaring back in the last year). DNA - Using dna to make molecular machines. Twisting them upon themselves to make molecular machines. I suppose those are the three big pathways. For awhile, STM's didn't seemed to be a dead end, till the last few months.
https://www.nanowerk.com/nanotechnology-news2/newsid=50736.php - These guys have figured out 1) how to keep the STM from destroying the sample. There was a problem of the STM tip crashing into the sample it was either imaging or creating. 2) they've been able to make structures at room temperature. Before, like when IBM spelled their name one atom at a time, back in teh 1980s, that structure only existed at very low temperatures. The electron microscope guys had the same problems. They could only image and manipulate atoms at very low temperatures - till recently.
There's another STM advancement which allows for massive parallel processing of atoms. It's by means of light actuation. I'm pretty sure these guys know of that. Either way, they mention that they think they can implement their advance with massive parallel ideas already thought of. I'd have to dig the article out. It was months ago. Science/technology moves so fast, that an article months ago is burried under so much new science announcements.
