  Multiparameter estimation theory offers a general framework to explore
imaging techniques beyond the Rayleigh limit. While optimal measurements of
single parameters characterizing a composite light source are now well
understood, simultaneous determination of multiple parameters poses a much
greater challenge that in general requires implementation of collective
measurements. Here we show, theoretically and experimentally, that
Hong-Ou-Mandel interference followed by spatially resolved detection of photons
provides precise information on both the separation and the centroid for a pair
of point emitters, avoiding trade-offs inherent to single-photon measurements.
