Which experiment first demonstrated quantum interference with large carbon molecules such as buckyballs?

The C₆₀ matter-wave interference experiment demonstrated quantum interference with large carbon molecules such as buckyballs.

In 1999, a team led by Anton Zeilinger observed diffraction and interference of fullerene molecules containing 60 carbon atoms. The molecules passed through a grating and produced an interference pattern, showing that wave–particle duality is not limited to electrons, atoms, or very small molecules.

A fullerene is a hollow carbon molecule; C₆₀ is commonly called buckminsterfullerene or a buckyball because its 60 carbon atoms form a cage resembling a truncated icosahedron. Its de Broglie wavelength is tiny, so the experiment required carefully controlled beams, gratings, and detection conditions.

The result did not mean that a macroscopic object visibly splits into classical copies. Rather, quantum amplitudes associated with alternative paths interfere when environmental interactions do not destroy the relevant coherence. Later experiments extended matter-wave interference to still larger molecules.