Quantum Interference Shown Experimentally in Larger Molecules


Particle-wave duality is one of the most mysterious facets of quantum physics. It states that every quantum object has properties of both a wave and a particle. This can be easily demonstrated using the double-slit experiment. Streams of particles directed at a barrier, facing the two narrow openings, create an interference pattern, as though they are waves. Neither a pure wave nor particle description has been able to successfully explain these experiments.

Researchers have now performed a quantum interference experiment with magnitudes larger and much more massive molecules than used before. The findings were published in the journal Nature Nanotechnology.


Thomas Young’s sketch of two-slit diffraction of light presented to the Royal Society in 1803

The experiment, where 100 atoms were launched at a barrier which was designed to minimize molecular interactions, approaches the macroscopic scale, delving into an area where macroscopic and quantum physics overlap. This offers scientists a way to study the transition that has been frustrating to explain.

In quantum physics, the wavelength of a massive particle is inversely proportional to its momentum since the mass is multiplied by the particle’s speed. The heavier an object, the shorter its wavelength at a given speed.

Longer wavelengths make it easier to generate interference patterns. The large pthalocyanine (C32H18N8) molecule and its derivatives (C48H26F24N8O8) have more mass than any others that have produced observable patterns of quantum interference. The molecules needed to move slowly to produce interference. This was accomplished by directing a blue diode laser onto a thin film of molecules in a vacuum chamber, boiling off individual molecules directly under the beam, leaving the rest undisturbed.

When they started the experiment, individual light spots started appearing in the fluorescent detector. Over time, these spots formed an interference pattern due to the wavelike character of the molecules.

Future experiments with even larger molecules might be able to examine the exact transition between macroscopic physics and quantum physics, providing insight into a grand unified theory of physics.

[via Ars Technica, images by Thomas Young/Wikipedia, and IUPUI]

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