  We show that it is possible to generate a novel single-photon fringe pattern
by using two spatially separated identical bi-photon sources. The fringes are
similar to the ones observed in a Michelson interferometer and possess certain
remarkable properties with potential applications. A striking feature of the
fringes is that although the pattern is obtained by detecting only one photon
of each photon pair, the fringes shift due to a change in the optical path
traversed by the undetected photon. The fringe shift is characterized by a
combination of wavelengths of both photons, which implies that the wavelength
of a photon can be measured without detecting it. Furthermore, the visibility
of the fringes diminishes as the correlation between the transverse momenta of
twin photons decreases: visibility is unity for maximum momentum correlation
and zero for no momentum correlation. We also show that the momentum
correlation between the two photons of a pair can be determined from the
single-photon interference pattern. We thus for the first time propose a method
of measuring a two-photon correlation without coincidence or heralded
detection.
