Topological conformal defects with tensor networks

The critical two-dimensional classical Ising model on the square lattice has two topological conformal defects: the Z2 symmetry defect Dε and the Kramers-Wannier duality defect Dσ. These two defects implement antiperiodic boundary conditions and a more exotic form of twisted boundary conditions, respectively. On the torus, the partition function ZD of the critical Ising model in the presence of a topological conformal defect D is expressed in …