  Non-Abelian defects that bind Majorana or parafermion zero modes are
prominent in several topological quantum computation schemes. Underpinning
their established understanding is the quantum Ising spin chain, which can be
recast as a fermionic model or viewed as a standalone effective theory for the
surface-code edge -- both of which harbor non-Abelian defects. We generalize
these notions by deriving an effective Ising-like spin chain describing the
edge of quantum-double topological order. Relating Majorana and parafermion
modes to anyonic strings, we introduce quantum-double generalizations of
non-Abelian defects. We develop a way to embed finite-group valued qunits into
those valued in continuous groups. Using this embedding, we provide a continuum
description of the spin chain and recast its non-interacting part as a quantum
wire via addition of a Wess-Zumino-Novikov-Witten term and non-Abelian
bosonization.
