  It is thought that schemes for quantum imaging are fragile against realistic
environments in which the background noise is often stronger than the
nonclassical signal of the imaging photons. Unfortunately, it is unfeasible to
produce brighter quantum light sources to alleviate this problem. Here, we
overcome this paradigmatic limitation by developing a quantum imaging scheme
that relies on the use of natural sources of light. This is achieved by
performing conditional detection on the photon number of the thermal light
field scattered by a remote object. Specifically, the conditional measurements
in our scheme enable us to extract quantum features of the detected thermal
photons to produce quantum images with improved signal-to-noise ratios. This
technique shows a remarkable exponential enhancement in the contrast of quantum
images. Surprisingly, this measurement scheme enables the possibility of
producing images from the vacuum fluctuations of the light field. This is
experimentally demonstrated through the implementation of a single-pixel camera
with photon-number-resolving capabilities. As such, we believe that our scheme
opens a new paradigm in the field of quantum imaging. It also unveils the
potential of combining natural light sources with nonclassical detection
schemes for the development of robust quantum technologies.
