  We study the generalized Young's double-slit interference for the beam
produced in the spontaneously parametric down-conversion (SPDC). We find that
the sub-wavelength lithography can occur macroscopically in both the two-photon
intensity measurement and the single-photon spatial intensity correlation
measurement. We show the visibility and the strength of the interference fringe
related to the SPDC interaction. It may provide a strong quantum lithography
with a moderate visibility in practical application.
