  We report on a nanoscale quantum-sensing protocol which tracks a free
precession of a single nuclear spin and is capable of estimating an azimuthal
angle---a parameter which standard multipulse protocols cannot determine---of
the target nucleus. Our protocol combines pulsed dynamic nuclear polarization,
a phase-controlled radiofrequency pulse, and a multipulse AC sensing sequence
with a modified readout pulse. Using a single nitrogen-vacancy center as a
solid-state quantum sensor, we experimentally demonstrate this protocol on a
single 13C nuclear spin in diamond and uniquely determine the lattice site of
the target nucleus. Our result paves the way for magnetic resonance imaging at
the single-molecular level.
