We have heard several years ago of quantum interference with C60 buckyballs, which are molecules containing 60 atoms. Now comes a new report of quantum interference of molecules, each containing 430 atoms, at around 6 nm in length!
In the team's experiment, the beams of molecules are passed through three sets of slits. The first slit, made from a slice of silicon nitride patterned with a grating consisting of slits 90 nanometres wide, forces the molecular beam into a coherent state, in which the matter waves are all in step. The second, a 'virtual grating' made from laser light formed by mirrors into a standing wave of light and dark, causes the interference pattern. The third grating, also of silicon nitride, acts as a mask to admit parts of the interference pattern to a quadrupole mass spectrometer, which counts the number of molecules that pass through.
The researchers report in Nature Communications today that this number rises and falls periodically as the outgoing beam is scanned from left to right, showing that interference, and therefore superposition, is present.
A very, very clever experiment, and it shows that if one can maintain coherence, size really doesn't matter in the manifestation of quantum effects.