Interference of mesoscopic particles: quantum-classical transition

Interference is one of the most characteristic traits ofquantum systems. As Dirac clarified, this phenomenon is rooted in thesuperposition principle, according to which different states of a singlequantum mechanical particle interfere with each other. Quantum particlesinterfere, but classical particles do not, and it is not easy tounderstand where the borderline has to be placed. The size of theinterfering system plays an important role, but it is certainly not theonly relevant variable: for example, double slit interference has beenobserved with molecules, but not with protons.

We analyze the doubleslit interference of a mesoscopic particle endowed with an internalstructure which leads to entanglement with its environment (e.g., viaphoton emission). An example is a fullerene molecule flying between adiffraction grating and a detector. We calculate the visibility of theinterference pattern, introduce a characteristic temperature thatdefines the onset to decoherence and scrutinize the conditions that mustbe satisfied for an interference experiment to be possible.