  We investigate effective noise channels for encoded quantum systems with and
without active error correction. Noise acting on physical qubits forming a
logical qubit is thereby described as a logical noise channel acting on the
logical qubits, which leads to a significant decrease of the effective system
dimension. This provides us with a powerful tool to study entanglement features
of encoded quantum systems. We demonstrate this framework by calculating lower
bounds on the lifetime of distillable entanglement and the negativity for
encoded multipartite qubit states with different encodings. At the same time,
this approach leads to a simple understanding of the functioning of
(concatenated) error correction codes.
