  Decoherence is the process by which quantum systems interact and become
correlated with their external environments; quantum trajectories are a
powerful technique by which decohering systems can be resolved into stochastic
evolutions, conditioned on different possible ``measurements'' of the
environment. By calling on recently-developed tools from quantum information
theory, we can analyze simplified models of decoherence, explicitly quantifying
the flow of information and randomness between the system, the environment, and
potential observers.
