  We report a photoluminescence imaging system for locating single quantum
emitters with respect to alignment features. Samples are interrogated in a 4~K
closed-cycle cryostat by a high numerical aperture (NA=0.9, 100$\times$
magnification) objective that sits within the cryostat, enabling high
efficiency collection of emitted photons without image distortions due to the
cryostat windows. The locations of single InAs/GaAs quantum dots within a
$>50$~$\mu$m~$\times$~50~$\mu$m field of view are determined with
$\approx4.5$~nm uncertainty (one standard deviation) in a 1~s long acquisition.
The uncertainty is determined through a combination of a maximum likelihood
estimate for localizing the quantum dot emission, and a cross-correlation
method for determining the alignment mark center. This location technique can
be an important step in the high-throughput creation of nanophotonic devices
that rely upon the interaction of highly confined optical modes with single
quantum emitters.

Quantum Physics;Mesoscale and Nanoscale Physics;Optics