Quantum state

Summary

A quantum state is the mathematical description of a quantum system at one moment, from which the probabilities of all measurement results follow. In the Hilbert space formulation it is a density operator on the Hilbert space of the system. The pure states are the unit vectors up to a phase factor, the points of the projective Hilbert space; the others are mixed states. The states form a convex set, whose extreme points are the pure states.