  We propose a high efficiency high fidelity measurement of the ground state
spin of a single NV center in diamond, using the effects of cavity quantum
electrodynamics. The scheme we propose is based in the one dimensional atom or
Purcell regime, removing the need for high Q cavities that are challenging to
fabricate. The ground state of the NV center consists of three spin levels
$^{3}A_{(m=0)}$ and $^{3}A_{(m=\pm1)}$ (the $\pm1$ states are near degenerate
in zero field). These two states can undergo transitions to the excited
($^{3}E$) state, with an energy difference of $\approx7-10$ $\mu$eV between the
two. By choosing the correct Q factor, this small detuning between the two
transitions results in a dramatic change in the intensity of reflected light.
We show the change in reflected intensity can allow us to read out the ground
state spin using a low intensity laser with an error rate of
$\approx5.5\times10^{-3}$, when realistic cavity and experimental parameters
are considered. Since very low levels of light are used to probe the state of
the spin we limit the number of florescence cycles, thereby limiting the non
spin preserving transitions through the intermediate singlet state $^{1}A$.
