PDF

A Quantum State Is an Incomplete Description, 3 pages.

Abstract

In a particular quantum state, it is possible for certain events either to have interference, or not to. The probabilities are different in each case, depending on whether the Born rule is applied before adding probabilities or after adding probability amplitudes. The state thus does not provide enough information to compute the correct probabilities: it is missing at least one bit, to indicate whether interference is present for those outcomes. A quantum state is therefore not a complete description of a system.