Interference with or without entanglement has been recognized as a key resource for quantum computingand quantum communications systems, as for example discussed by Nielsen and Chuang1 and numerous otherworks. Multiple paths between sources and detectors require an understanding of the underpinning wave-particleduality issue in the interference effects. Recently a new axiom (particle and its wave function ψ(r, t) cannot becoincident or co-located at space-time point (r_k, t_k) unless ψ(r, t) = δ(r-r_k, t-t_k) the Dirac delta function) has beensuggested and justified, which explains duality without Niels Bohr’s complementarity principle, thus eliminatingthe role of the observer, avoiding complicated “which way” (welcher-weg) considerations and observer subjectivity.This greatly simplifies analysis and design of multi-path quantum systems and restores objectivity. The same paperalso suggested in the context of entanglement new concepts of (a) “total causality” that includes entanglement as acause to locally and causally explain “action at a distance”, and (b) “partial causality” that excludes entanglement asa cause and thereby introduces the perception of strange phenomena of non-locality, retro-causality and quantumerasure, which are nevertheless very important. This paper reviews and then applies the axiom to bring much neededclarity to certain confusing and much debated aspects of developments in non-interaction measurements,counterfactual communications and quantum computers. These potential clarifications and simplifications ofanalysis and design of multi path systems may help developers of future quantum communication and quantumcomputer systems.
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