Heisenberg optical near-field microscope

It is proven that in molecular interferometry a which-path information can be recorded using detection of spontaneously emitted photons of long wavelengths in the optical near field of the apertures. This does not, however, contradict Heisenberg's uncertainty principle: It is shown that even if the momentum transfer in this experiment is negligible, the entanglement between the detector molecule and photon is responsible for the loss of coherence.