  The field of nanoscale magnetic resonance imaging (NanoMRI) was started 30
years ago. It was motivated by the desire to image single molecules and
molecular assemblies, such as proteins and virus particles, with near-atomic
spatial resolution and on a length scale of 100 nm. Over the years, the NanoMRI
field has also expanded to include the goal of useful high-resolution nuclear
magnetic resonance (NMR) spectroscopy of molecules under ambient conditions,
including samples up to the micron-scale. The realization of these goals
requires the development of spin detection techniques that are many orders of
magnitude more sensitive than conventional NMR and MRI, capable of detecting
and controlling nanoscale ensembles of spins. Over the years, a number of
different technical approaches to NanoMRI have emerged, each possessing a
distinct set of capabilities for basic and applied areas of science. The goal
of this roadmap article is to report the current state of the art in NanoMRI
technologies, outline the areas where they are poised to have impact, identify
the challenges that lie ahead, and propose methods to meet these challenges.
This roadmap also shows how developments in NanoMRI techniques can lead to
breakthroughs in emerging quantum science and technology applications.
