The collapse of a quantum state as a signal analytic sleight of hand
Peter Morgan
Abstract
The collapse of a quantum state is a mathematical sleight of hand that allows the construction of a joint probability density even for operators that are noncommutative. We can formalize that construction as a non-commutative, non-associative collapse product that is nonlinear in its left operand as a model for joint measurements at time-like separation, in part inspired by the sequential product for positive semi-definite operators. A collapse picture, in which a quantum state collapses after each measurement, can therefore be equivalent to a no-collapse picture that uses a different state and different, mutually commutative, Quantum Non-Demolition operators to construct the same joint probability density for consecutive measurements. The collapse of a state is a mathematical construction that can also be a useful tool when using the Koopman formalism for classical mechanics and signal analysis.