EXTENDED FEYNMAN RULE AND THE 2-SLIT EXPERIMENT

An extension of Feynman's rule, relating probability amplitudes and pr obabilities in two-photon interferometry, has been proposed recently [ G. Jaeger et al., Phys. Rev. A 48, 1023 (1993)]. It would be interesti ng to analyze the validity of this rule in other physical situations n ot considered by these authors. In particular, we show in this paper t hat the extended rule cannot be applied to the gedanken two-slit exper iment. This result suggests the existence of two quantum regimes, diff erentiated by the validity of the generalized rule. The distinguishabi lity of one particle and the visibilities of one-particle and two-part icle interferences are calculated.