1. Introduction: the territory
The atomic nucleus is placed at the center of the quantum ladder: it provides a connection
between the smallest and the largest, see figure 1. Being a congregation of neutrons and
protons, it emerges from complex interactions between quarks and gluons on a scale of
femtometers. But its properties also determine the behavior of giant stars on a gigameter scale.
Indeed, nuclear structure encompasses phenomena over an incredibly wide range of energies
and distances. Atomic nuclei are laboratories of fundamental laws of nature, and thus linked
to particle physics. At the same time, nuclei exhibit behaviors that are emergent in nature and
present in other complex systems studied by condensed matter physicists and quantum
chemists. The general challenge for the interdisciplinary field of nuclear structure—the
nuclear many-body problem—is to understand the principles of building up nuclear