  Nitrogen-Vacancy (NV) centers in diamond have been used in recent years for a
wide range of applications, from nano-scale NMR to quantum computation. These
applications depend strongly on the efficient readout of the NV center's spin
state, which is currently limited. Here we suggest a method of reading the NV
center's spin state, using the weak optical transition in the singlet manifold.
We numerically calculate the number of photons collected from each spin state
using this technique, and show that an order of magnitude enhancement in spin
readout signal-to-noise ratio is expected, making single-shot spin readout
within reach. Thus, this method could lead to an order of magnitude enhancement
in sensitivity for ubiquitous NV based sensing applications, and remove a major
obstacle from using NVs for quantum information processing.
