  The quantum nature of optical near-fields is interesting from a theoretical
perspective and of importance for practical applications, such as
high-resolution imaging, sensing and antenna-coupled quantum light sources. In
this work we use a custom-designed superconducting nanowire single-photon
detector (SNSPD) to directly read out the near-field interaction between source
and detector. We use a subwavelength-sized aperture at the end of an optical
fiber to record spatial near-field maps and to measure the distance dependence
of the optical near-field interaction. Our measurements can be well described
by a superposition of evanescent source fields with no noticeable probe-sample
coupling. Our approach can be used for further studies of quantum near-field
interactions and for the development of near-field imaging techniques with
single quantum sensitivity.
