  An unusual regime for liquid-state nuclear magnetic resonance (NMR) where the
magnetic field strength is so low that the $J$-coupling (intramolecular
spin-spin) interactions dominate the spin Hamiltonian opens a new paradigm with
applications in spectroscopy, quantum control, and in fundamental-physics
experiments, including searches for well-motivated dark-matter candidates. An
interesting possibility is to bring this kind of "extreme NMR" together with
another one---single nuclear spin detected with a single-spin quantum sensor.
This would enable single-molecule $J$-spectroscopy.
