Single molecules in a quantum movie

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The quantum physics of massive particles has intrigued physicists for more than 80 years, since it predicts that even complex particles can exhibit wave-like behaviour – in conflict with our everyday ideas of what is real or local. An international team of scientists now succeeded in shooting a movie which shows the build-up of a matter-wave interference pattern from single dye molecules which is so large (up to 0.1 mm) that you can easily see it with a camera. This visualizes the dualities of particle and wave, randomness and determinism, locality and delocalization in a particularly intuitive way. Seeing is believing: the movie by Thomas Juffmann et al. is published on March 25 in "Nature Nanotechnology".

A quantum premiere with dye molecules as leading actors
Physicist Richard Feynman once claimed that interference effects caused by matter-waves contain the only mystery of quantum physics. Understanding and applying matter waves for new technologies is also at the heart of the research pursued by the Quantum Nanophysics team around Markus Arndt at the University of Vienna and the Vienna Center for Quantum Science and Technology.

The scientists now premiered a movie which shows the build-up of a quantum interference pattern from stochastically arriving single phthalocyanine particles after these highly-fluorescent dye molecules traversed an ultra-thin nanograting. As soon as the molecules arrive on the screen the researchers take live images using a spatially resolving fluorescence microscope whose sensitivity is so high that each molecule can be imaged and located individually with an accuracy of about 10 nanometers. This is less than a thousandth of the diameter of a human hair and still less than 1/60 of the wavelength of the imaging light.

A breath of nothing
In these experiments van der Waals forces between the molecules and the gratings pose a particular challenge. These forces arise due to quantum fluctuations and strongly affect the observed interference pattern. In order to reduce the van der Waals interaction the scientists used gratings as thin as 10 nanometers (only about 50 silicon nitride layers). These ultra-thin gratings were manufactured by the nanotechnology team around Ori Cheshnovski at the Tel Aviv University who used a focused ion beam to cut the required slits into a free-standing membrane.