  We present a method to directly detect the axion dark matter using nitrogen
vacancy centers in diamonds. In particular, we use metrology leveraging the
nuclear spin of nitrogen to detect axion-nucleus couplings. This is achieved
through protocols designed for dark matter searches, which introduce a novel
approach of quantum sensing techniques based on the nitrogen vacancy center.
Although the coupling strength of the magnetic fields with nuclear spins is
three orders of magnitude smaller than that with electron spins for
conventional magnetometry, the axion interaction strength with nuclear spins is
the same order of magnitude as that with electron spins. Furthermore, we can
take advantage of the long coherence time by using the nuclear spins for the
axion dark matter detection. We show that our method is sensitive to a broad
frequency range $\lesssim 100\,\mathrm{Hz}$ corresponding to the axion mass
$m_a \lesssim 4\times 10^{-13}\,\mathrm{eV}$. We present the detection limit of
our method for both the axion-neutron and the axion-proton couplings and
discuss its significance in comparison with other proposed ideas.
