  Quantum error correction procedures have the potential to enable faithful
operation of large-scale quantum computers. They protect information from
environmental decoherence by storing it in logical qubits, built from ensembles
of entangled physical qubits according to suitably tailored quantum error
correcting encodings. To date, no generally accepted framework to characterise
the behaviour of logical qubits as quantum memories has been developed. In this
work, we show that generalisations of well-established figures of merit of
physical qubits, such as relaxation times, to logical qubits fail and do not
capture dynamics of logical qubits. We experimentally illustrate that, in
particular, spatial noise correlations can give rise to rich and
counter-intuitive dynamical behavior of logical qubits. We show that a suitable
set of observables, formed by code space population and logical operators
within the code space, allows one to track and characterize the dynamical
behaviour of logical qubits. Awareness of these effects and the efficient
characterisation tools used in this work will help to guide and benchmark
experimental implementations of logical qubits.
