  Analyses based on quantum metrology have shown that the ability to localize
the positions of two incoherent point sources can be significantly enhanced
through the use of mode sorting. Here we theoretically and experimentally
investigate the effect of partial coherence on the sub-diffraction limit
localization of two sources based on parity sorting. With the prior information
of a negative and real-valued degree of coherence, higher Fisher information is
obtained than that for the incoherent case. Our results pave the way to
clarifying the role of coherence in quantum limited metrology.
