  Quantum technologies are poised to move the foundational principles of
quantum physics to the forefront of applications. This roadmap identifies some
of the key challenges and provides insights on materials innovations underlying
a range of exciting quantum technology frontiers. Over the past decades,
hardware platforms enabling different quantum technologies have reached varying
levels of maturity. This has allowed for first proof-of-principle
demonstrations of quantum supremacy, for example quantum computers surpassing
their classical counterparts, quantum communication with reliable security
guaranteed by laws of quantum mechanics, and quantum sensors uniting the
advantages of high sensitivity, high spatial resolution, and small footprints.
In all cases, however, advancing these technologies to the next level of
applications in relevant environments requires further development and
innovations in the underlying materials. From a wealth of hardware platforms,
we select representative and promising material systems in currently
investigated quantum technologies. These include both the inherent quantum bit
systems as well as materials playing supportive or enabling roles, and cover
trapped ions, neutral atom arrays, rare earth ion systems, donors in silicon,
color centers and defects in wide-band gap materials, two-dimensional materials
and superconducting materials for single-photon detectors. Advancing these
materials frontiers will require innovations from a diverse community of
scientific expertise, and hence this roadmap will be of interest to a broad
spectrum of disciplines.
