  Biphoton states of signal and idler fields--obtained from spontaneous
parametric downconversion (SPDC) in the low-brightness, low-flux regime--have
been utilized in several quantum imaging configurations to exceed the
resolution performance of conventional imagers that employ coherent-state or
thermal light. Recent work--using the full Gaussian-state description of
SPDC--has shown that the same resolution performance seen in quantum optical
coherence tomography and the same imaging characteristics found in quantum
ghost imaging can be realized by classical-state imagers that make use of
phase-sensitive cross correlations. This paper extends the Gaussian-state
analysis to two additional biphoton-state quantum imaging scenarios: far field
diffraction-pattern imaging; and broadband thin-lens imaging. It is shown that
the spatial resolution behavior in both cases is controlled by the nonzero
phase-sensitive cross correlation between the signal and idler fields. Thus,
the same resolution can be achieved in these two configurations with
classical-state signal and idler fields possessing a nonzero phase-sensitive
cross correlation.
