Electrons are still very small particles, so the question arises as to whether quantum weirdness extends to larger objects. The experimental answer is yes!
In 1988, Austrian physicist Anton Zeilinger performed the basic interference experiment with neutrons.29 In 1991, Carnal and Mlynek did the same with helium atoms.30 In 1999, Markus Arndt, Anton Zeilinger, and co-workers31 at the University of Vienna in Austria sent a collimated beam of carbon-60 “buckyball” molecules through a slit made of silicon nitride and detected the interference pattern by ionizing the molecules with a laser and then counting the ions. The slits in the diffraction grating were 50-nm wide and the grating had a period of 100 nm. The central maximum and the two first-order diffraction peaks in the interference pattern were detected with single molecules flying through the apparatus, confirming interference effects predicted by quantum mechanics. The molecules had a most probable velocity of 220 m/s, which corresponds to a de Broglie wavelength of 2.5 × 10−12 m, which is approximately 400 times smaller than the diameter of the C60 Buckminsterfullerene molecule.
More recently, the Vienna team performed an improved experiment with fluorinated buckyballs.32 These biological molecules are present in chlorophyll and have a diameter of about 2 nm, which is over twice as big as a C60 Buckminsterfullerene molecule. The team has also reported a successful interference experiment with a fullerene compound that contains 60 carbon and 48 fluorine atoms, making this the most complex object to show two-slit interference to date.
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