Wave–particle duality of C60 molecules

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   It is not only electrons that make bands. In 1999, football-shaped molecules of 60 carbon atoms made interference bands, and in 2019 molecules with almost 2,000 atoms did. There is no known border where quantum physics stops; there are only objects ever harder to keep untouched.

   Wave–particle duality of C60 molecules · 1999

   There is no known border of the quantum world, only objects ever harder to leave alone.

   If electrons make bands, maybe there is something special about them, being so small and light? Physicists tried ever larger objects: atoms, then molecules. In 1999 Anton Zeilinger and Markus Arndt's team in Vienna sent fullerene molecules, called C60, through a grid of very fine slits. A fullerene has 60 carbon atoms arranged exactly like the patches of a football. The molecule is more than a million times heavier than an electron. And yet it made interference bands. The record has grown since. In 2019 the same group got bands with molecules made of almost 2,000 atoms, more than 25,000 times heavier than a hydrogen atom. That took a two-metre apparatus in a very good vacuum, where the molecules fly while touching almost nothing. So why does a cat not make bands? Two reasons. First: the heavier an object, the shorter its wave, and the bands end up so close together that no instrument could tell them apart. Second, and more important: a cat is touched all the time by air, by light and by its own heat, so decoherence, from the last lesson, wipes its bands out almost instantly. No border is known where quantum physics stops. Only objects that are ever harder to keep isolated.

   “This molecule is the most massive and complex object in which wave behaviour has been observed. Of particular interest is the fact that C60 is almost a classical body, because of its many excited internal degrees of freedom and their possible couplings to the environment.”

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