  Fundamental wave features of light play an important role in the realization
of superresolution for two spatially separated point sources. It has been shown
that (partial) coherence, which is an inevitable feature in practical light
propagation, is harmful to measurement precision thus preventing
superresolution. Here we study the quantitative effect of another fundamental
feature, entanglement, on the quality of superresolution and compare it with
that of coherence. Both single- and two-parameter estimations are analyzed in
detail. Surprisingly, contrary to coherence, it is found that superresolution
measurement precision (in terms of Fisher Information) can be enhanced as the
amount of entanglement increases. More importantly, our analysis shows that
non-zero entanglement always guarantees the non-vanishing of Fisher
Information. Thus, while coherence is unwanted, entanglement is a favorable
feature for superresolution.
