Environment-induced superselection: pointer states survive decoherence
Purity Tr(ρ²) = 1.00 | Coherence = 1.00
Zurek's einselection: when a quantum system couples to its environment, only certain "pointer states"
remain stable — they are the eigenstates of the system-environment interaction Hamiltonian.
Decoherence destroys off-diagonal density matrix elements (quantum coherence) at rate γ,
leaving a classical mixture while preserving the pointer basis populations.