  Topologically ordered phases of matter, in particular so-called symmetry
enriched topological (SET) phases, can exhibit quantum number fractionalization
in the presence of global symmetry. In Z_2 topologically ordered states in two
dimensions, fundamental translations T_x and T_y acting on anyons can either
commute or anticommute. This property, crystal momentum fractionalization, can
be seen in a periodicity of the excited-state spectrum in the Brillouin zone.
We present a numerical method to detect the presence of this form of symmetry
enrichment given a projected entangled pair state (PEPS); we study the minima
of spectrum of correlation lengths of the transfer matrix for a cylinder. As a
benchmark, we demonstrate our method using a modified toric code model with
perturbation. An enhanced periodicity in momentum clearly reveals the
anticommutation relation {T_x,T_y}=0$ for the corresponding quasiparticles in
the system.
