New Interpretation of the Scalar Product in Hilbert Space
Yakir Aharonov, David Z. Albert, Cheuk Kwan Au · Physical Review Letters · 1981
The inner product of two states in Hilbert space is interpreted in terms of a relationship between two or more distinct physical systems. This point of view suggests a generalized notion of measurement, within which the familiar types of measurement occur as special cases. A variety of novel measuring procedures are described, which relate overcomplete sets of states for a given system to complete sets for some larger system (of which the smaller system forms a part).