  A novel quantum imaging technique has recently been demonstrated in an
experiment, where the photon used for illuminating an object is not detected;
the image is obtained by interfering two beams, none of which ever interacts
with the object. Here we present a detailed theoretical analysis of the
experiment. We show that the object information is present only in the
interference term and not in the individual intensities of the interfering
beams. We also theoretically establish that the magnification of the imaging
system depends on two wavelengths: the average wavelength of the photon that
illuminates the object and the average wavelength of the photon that is
detected. Our analysis affirms that the imaging process is based on the
principle that quantum interference occurs when interferometric path
information is unavailable.
