Nature Nanotech. http://doi.org/htz (2012)

The visual signature of wave–particle duality — the interference pattern in the famous double-slit experiment — is distinctively beautiful. Now Thomas Juffmann and co-workers have captured images of the interference pattern formed by large single molecules as the pattern builds — a real-time film of 'quantum mechanics in action'.

Since the first double-slit experiments using particles other than photons were performed in the 1960s, the particles in question have been getting bigger: from electrons to neutrons, to atoms and molecules. Meanwhile, the slits have been scaled down, now reaching the nanometre scale. Combining nanofabrication and nano-imaging techniques, Juffmann et al. have gone a step further and pushed the current experimental limits towards the boundary between quantum and classical physics.

Using a laser-controlled micro-evaporation source, they produced a collimated beam of phthalocyanine molecules or derivatives, having masses between 500 and 1,300 atomic mass units. With the beam directed at a nanometre-size grating and using high-resolution fluorescence microscopy, the authors recorded the developing interference pattern as the molecules passed through the grating and arrived at the detector one by one.