Controlling molecular binding at the level of single
atoms is one
of the holy grails of quantum chemistry. Rydberg macrodimers—bound
states between highly excited Rydberg atoms—provide a novel
perspective in this direction. Resulting from binding potentials formed
by the strong, long-range interactions of Rydberg states, Rydberg
macrodimers feature bond lengths in the micrometer regime, exceeding
those of conventional molecules by orders of magnitude. Using single-atom
control in quantum gas microscopes, the unique properties of these
exotic states can be studied with unprecedented control, including
the response to magnetic fields or the polarization of light in their
photoassociation. The high accuracy achieved in spectroscopic studies
of macrodimers makes them an ideal testbed to benchmark Rydberg interactions,
with direct relevance to quantum computing and information protocols
where these are employed. This review provides a historic overview
and summarizes the recent findings in the field of Rydberg macrodimers.
Furthermore, it presents new data on interactions between macrodimers,
leading to a phenomenon analogous to Rydberg blockade at the level
of molecules, opening the path toward studying many-body systems of
ultralong-range Rydberg molecules.