  Single atoms provide an ideal system for utilizing fundamental quantum
functions. Their electrons have well-defined energy levels and spin properties.
Even more importantly, for a given isotope -- say, $^{12}$C -- all the atoms
are identical. This creates a perfect uniformity that is impossible to achieve
in macroscopic-size quantum systems. However, herding individual atoms is a
very difficult task that requires trapping them with magnetic or optical means
and cooling them down to temperatures in the nanokelvin range. On the other
hand, the counterpart of single atoms -- the single defects -- may be as good
as atom-based quantum systems if not better. These defects, also referred as
quantum defects, possess the favorable energy, spin, and uniformity properties
of single atoms and remain in their place without the help of precisely tuned
lasers. While the number of usable isotopes is set, the combinations of defects
and their host material are practically limitless, giving us the flexibility to
create precisely designed and controlled quantum systems. Furthermore, as we
tame these defects for the quantum world, we bring about transformative
opportunities to the classical world in forms such as ultradense electronic
devices and precise manufacturing. In this research insight, we introduce some
of our recent work on precisely controlled creation and manipulation of
individual defects with a scanning tunneling microscope (STM). We also discuss
possible pathways for utilizing these capabilities for the development of novel
systems for Quantum Information Science (QIS) applications such as quantum
information processing and ultrasensitive sensors.
