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Wave--particle duality is frequently the first topic students encounter in elementary quantum physics. Although this phenomenon has been demonstrated with photons, electrons, neutrons, and atoms, the dual quantum character of the famous double-slit experiment can be best explained with the largest and most classical objects, which are currently the fullerene molecules. The soccer-ball-shaped carbon cages [C.sub.60] are large, massive, and appealing objects for which it is clear that they must behave like particles under ordinary circumstances. We present the results of a multislit diffraction experiment with such objects to demonstrate their wave nature. The experiment serves as the basis for a discussion of several quantum concepts such as coherence, randomness, complementarity, and wave--particle duality. In particular, the effect of longitudinal (spectral) coherence can be demonstrated by a direct comparison of interferograms obtained with a thermal beam and a velocity selected beam in close analogy to the usual two-slit experiments using light. [DOI: 10.1119/1.1531580]

It has been possible to observe de Broglie wave interference of C60 molecules by diffraction at a material absorption grating. All the observations supported the view that each C60 molecule interferes only with itself. C60 is nearly a classical body, as a result of its many excited internal degrees of freedom and their potential couplings to the environment. Further research should consider the interference of objects the size of which is equal to or even larger than the diffracting structure.