  In 1989, Eigler and Schweizer spelt the letters IBM by positioning 35
individual Xenon atoms at 4 Kelvin temperature. The arrangement took
approximately 22 hours. This was an outstanding demonstration of control over
individual atoms. Since then, 3D printers developed into a near-ubiquitous
technology. Nevertheless, with typical resolutions in the micrometres, they are
far from the atomic scale of control that the IBM demonstration seemed to
herald. Even the highest resolution achieved with ultrafast lasers driving
two-photon polymerization barely reaches 100 nm, three orders of magnitude
distant from the atomic scale. Here, we adopt a long-term view when we ask
about the possibility of a 3D atom printer, which can build an arbitrarily
shaped object of macroscopic dimensions with control over its atomic structure
at room temperature. After discussing the state-of-the-art technology based on
direct laser writing, we identify three fundamental challenges. The first is
the fat fingers problem, i.e., laser wavelengths are much larger than the size
of the atoms. The second one is complexity explosion; namely, the number of
processing steps scales with the inverse cube of the resolution, leading to
prohibitively long processing times. The third challenge is the increasing
strength of random fluctuations as we approach the atomic scale. This requires
control over the fluctuations, which we call mischief of fluctuations. Although
direct-writing techniques offer sufficient resolution, speed, and excellent
flexibility for the mesoscopic scale, each of the three fundamental problems
appears enough to render the atomic scale unreachable. In contrast, these three
challenges are not fundamental limitations to self-organisation. We propose a
potential path to a 3D atom printer, where laser-driven self-organisation can
complement direct-writing techniques by bridging the atomic and mesoscopic
scales.
