Entanglement, joint measurement, and state reduction

Macdonald, Alan (2003) Entanglement, joint measurement, and state reduction.

Abstract

Entanglement has been called the most important new feature of the quantum world. It is expressed in the quantum formalism by the joint measurement formula. We prove the formula for projection valued observables from a plausible assumption, which for spacelike separated measurements is an expression of relativistic causality. The state reduction formula is simply a way to express the joint measurement formula after one measurement has been made, and its result known.