  Quantum information technology is one of the fastest growing sectors within
information technology. By misleading interpretations of Bohr's definition of
complementarity, the foundation of nonlocal correlations of entanglement is
concealed and therefore, such nonlocal effects can apparently not be utilized
directly in information technology. As the first step to identify the
utilizable nonlocal property of entanglement, this paper adjusts the notion of
complementarity of first-order and second-order interference. Especially, the
nonlocal consequence of the "principle of least action" for entangled systems
is shown by the foundation of second-order interference, the shared phase
solutions space. Based on the concept of Feynman's path integral, the validity
of the theory is demonstrated by applying the theory to well-known experiments,
revealing this underlying nonlocal principle. In the next steps of publication,
to highlight the relevance of this nonlocal principle for quantum computing and
quantum information technology, the "self-consistency principle" of such
nonlocal quantum causal correlations will be shown and verified by an
experiment.
