  Novel imaging techniques utilizing nondegenerate, correlated photon pairs
sparked intense interest during the last couple of years among scientists of
the quantum optics community and beyond. It is a key property of such "ghost
imaging" or "quantum interference" methods that they use those photons of the
correlated pairs for imaging that never interacted with the sample, allowing
detection in a spectral range different from that of the illumination of the
object. Extensive applications of these techniques in spectroscopy and
microscopy are envisioned, however, their limited spatial resolution to date
has not yet supported real-life microscopic investigations of tiny biological
objects. Here we report a modification of the method based on quantum
interference by using a seeding laser and confocal scanning, that allows the
improvement of the resolution of imaging with undetected photons by more than
an order of magnitude, and we also present examples of application in the
microscopy of biological samples.
