The simulation shows the density matrices for both pure and mixed states of spin-1/2 particles in a Stern-Gerlach Apparatus (SGA). The user is able to orient a non-uniform magnetic field along either the x or z-axis in order to visualize the density matrix for both in the z-basis. Immediately before and after the magnetic field, both spin-up and spin-down (mixed) states are considered where the user can see the density matrix, whose trace is less than 1. Also, the user can see the density matrix for the separated (pure) states whose traces are 1. Both trace conditions are expected for mixed and pure states respectively. There is the ability to show information for either mixed states, pure states or both. Included with the simulation, is a step-by-step explanation of mixed and pure states and how the respective density matrix is calculated, including its trace.

This simulation is part of a collection of animations/simulations for the teaching of concepts in quantum mechanics.