  Nuclear spins in solids exhibit long coherence times due to the small nuclear
gyromagnetic ratio. This weak environmental coupling comes at the expense of
slow quantum gate operations, which should be as fast as possible for many
applications in quantum information processing and sensing. In this work, we
use nitrogen-vacancy (NV) centers in diamond to probe the nuclear spins within
dark paramagnetic nitrogen defects (P1 centers) in the diamond lattice. The
gyromagnetic ratio of the P1 nuclear spin is augmented by hyperfine coupling to
the electron spin, resulting in greatly enhanced coupling to radiofrequency
control fields. We then demonstrate that this effect can be tuned by variation
of an external magnetic field. Our work identifies regimes in which we are able
to implement fast quantum control of dark nuclear spins, and lays the
foundations for further inquiry into rapid control of long-lived spin qubits at
room temperature.
