Unitary density evolution
Schrödinger time evolution:
If initially
- ?(x,x',0) = |?(x,0)> < ?(x',0)|
then the density matrix stays pure:
- ?(x,x',t) = |?(x,t)> < ?(x',t)|
- where ih ??(x,t)/?t = H ?(x,t) describes evolution according to the Schrödinger equation.