  There has been recent interest in conformal twisted boundary conditions and
their realisations in solvable lattice models. For the Ising and Potts quantum
chains, these amount to boundary terms that are related to duality, which is a
proper symmetry of the model at criticality. Thus, at criticality, the
duality-twisted Ising model is translationally invariant, similar to the more
familiar cases of periodic and antiperiodic boundary conditions. The complete
finite-size spectrum of the Ising quantum chain with this peculiar boundary
condition is obtained.
