Two-particle interference

The superposition principle leads to coherence phenomena that have no count erpart in classical optics. A gedanken experiment, due to Horne and Zeiling er, provides an especially clear illustration of such phenomena, and is pre sented in a manner suitable to an introductory quantum mechanics course. Th e experiment displays an interference pattern in the correlation between tw o particles produced in a momentum-conserving decay, but no interference pa ttern when either particle is observed separately; it also has interesting Einstein-Podolsky-Rosen-type correlations. (C) 2000 American Association of Physics Teachers.