Wave-particle duality visualized in quantum movie

March 27, 2012
interference pattern

Quantum interference pattern from phthalocyanine molecules (credit: Juffmann et al./Nature Nanotechnology)

An international team of scientists has shot a video that shows the build-up of a matter-wave interference pattern from single dye molecules. The pattern is so large (up to 0.1 mm), it can been seen with a video camera.

The video visualizes the dualities of particle and wave, randomness and determinism, and locality and delocalization in an intuitive way.

Physicist Richard Feynman once claimed that interference effects caused by matter-waves contain the only mystery of quantum physics, as he explained in another video (below).

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.

This is a high-tech version of the double slit experiment, which illustrates wave-particle duality. The wave nature of matter causes the dye molecules passing through the nano grating to interfere, producing the bright and dark vertical bands seen in the video — a result that would not be expected for discrete particles. However, the molecules are always detected as discrete particles (the dots seen in the video).

A quantum premiere with dye molecules as leading actors

The video shows the build-up of a quantum interference pattern from stochastically arriving single phthalocyanine fluorescent-dye molecules after they traversed an ultra-thin nanograting. These represent the most massive molecules in quantum far-field diffraction so far.

The researchers used 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.


Buildup of quantum interference (credit: Juffmann et al./Nature Nanotechnology)

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. To reduce the van der Waals interaction, the scientists used the 10 nanometers gratings.


The chemical structure of the phthalocyanine dye molecule (credit: Juffmann et al./Nature Nanotechnology)

These new technologies for generating, diffracting and detecting molecular beams will be important for extending quantum interference experiments to more and more complex molecules and for atomic interferometry, according to the researchers.

The experiments reveal the single-particle character of complex quantum diffraction patterns on a macroscopic scale that is visible in real time. The experiments also allow for studying molecular properties of solids and point the way towards future diffraction studies of atomically thin membranes.

Ref.: Thomas Juffmann, et al., Real-time single-molecule imaging of quantum interference, Nature Nanotechnology, 2012; [DOI: 10.1038/NNANO.2012.34] (open access)

In this video, Richard Feynman explains the interference effects caused by matter-waves in the classical double slit experiment.