° ow in entangled quantum systems

All information in quantum systems is, notwithstanding Bell’s theorem, localized. Measuring or otherwise interacting with a quantum system S has no e¬ect on distant systems from which S is dynamically isolated, even if they are entangled with S. Using the Heisenberg picture to analyse quantum information processing makes this locality explicit, and reveals that under some circumstances (in particular, in Einstein{Podolsky{Rosen experiments and in quantum teleportation), quantum information is transmitted through `classical’ (i.e. decoherent) information channels.