  Qubit technologies using nitrogen-vacancy color centers in diamonds require
precise knowledge of the centers, including the number of emitters within a
diffraction-limited spot and their orientations. However, the number of
emitters is challenging to determine when there is finite background, which
affects the precision of resulting quantum protocols. Here we show the
photoluminescence (PL) intensity and quantum correlation (Hanbury Brown and
Twiss) measurements as a function of polarization for one- and two-emitter
systems. The sample was made by implanting low concentrations of adenine
(C5H5N5) into a low nitrogen chemical vapor deposition diamond. This approach
yielded well-spaced regions with few nitrogen-vacancy centers. By mapping the
PL intensity and quantum correlation as a function of polarization, we can
distinguish two emitter systems from single emitters with background, providing
a method to quantify the background signal at implanted sites, which might be
different from off-site background levels. This approach also provides a
valuable new all-optical mechanism for the determination of one or two emitter
systems useful for quantum sensing, communication, and computation tasks.
