${\mathbb{Z}}_2$ topologically ordered phases on a simple hyperbolic lattice

Abstract

In this work, we consider 2D ${\mathbb{Z}}_2$ topologically ordered phases (${\mathbb{Z}}_2$ toric code and the modified surface code) on a simple hyperbolic lattice. Introducing a 2D lattice consisting of the product of a 1D Cayley tree and a 1D conventional lattice, we investigate two topological quantities of the ${\mathbb{Z}}_2$ topologically ordered phases on this lattice: the ground state degeneracy on a closed surface and the topological entanglement entropy. We find that both quantities depend on the number of branches and the generation of the Cayley tree. We attribute these results to a huge number of superselection sectors of anyons.

33 pages, 10 figures