Editing Convex hull (section)

===Quantum physics===
In [[quantum physics]], the [[state space]] of any quantum system — the set of all ways the system can be prepared — is a convex hull whose extreme points are [[positive-semidefinite matrix|positive-semidefinite operators]] known as pure states and whose interior points are called mixed states.{{sfnp|Rieffel|Polak|2011}} The [[Schrödinger–HJW theorem]] proves that any mixed state can in fact be written as a convex combination of pure states in multiple ways.{{sfnp|Kirkpatrick|2006}}