  For the past three decades, nanoscience has widely affected many areas in
physics, chemistry, and engineering, and has led to numerous fundamental
discoveries as well as applications and products. Concurrently, quantum science
and technology has developed into a cross-disciplinary research endeavour
connecting these same areas and holds a burgeoning commercial promise. Although
quantum physics dictates the behaviour of nanoscale objects, quantum coherence,
which is central to quantum information, communication and sensing has not
played an explicit role in much of nanoscience. This Review describes
fundamental principles and practical applications of quantum coherence in
nanoscale systems, a research area we call quantum-coherent nanoscience. We
structure this manuscript according to specific degrees of freedom that can be
quantum-coherently controlled in a given nanoscale system such as charge, spin,
mechanical motion, and photons. We review the current state of the art and
focus on outstanding challenges and opportunities unlocked by the merging of
nanoscience and coherent quantum operations.
