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Real-time single-molecule imaging of quantum interference

The observation of interference patterns in double-slit experiments with massive particles is generally regarded as the ultimate demonstration of the quantum nature of these objects. Such matter-wave interference has been observed for electrons, neutrons, atoms and molecules and it differs from classical wave-physics in that it can even be observed when single particles arrive at the detector one by one. The build-up of such patterns in experiments with electrons has been described as the "most beautiful experiment in physics". Here we show how a combination of nanofabrication and nanoimaging methods allows us to record the full two-dimensional build-up of quantum diffraction patterns in real-time for phthalocyanine molecules PcH2 and their tailored derivatives F24PcH2 with a mass of 1298 amu. A laser-controlled micro-evaporation source was used to produce a beam of molecules with the required intensity and coherence and the gratings were machined in 10 nm thick silicon nitride membranes to reduce the effect of van der Waals forces. Wide-field fluorescence microscopy was used to detect the position of each molecule with an accuracy of 10 nm and to reveal the build-up of a deterministic ensemble interference pattern from stochastically arriving and internally hot single molecules.