Stability of the bulk gap for frustration-free topologically ordered quantum lattice systems
arXiv:2102.07209
Abstract
We prove that uniformly small short-range perturbations do not close the bulk gap above the ground state of frustration-free quantum spin systems that satisfy a standard local topological quantum order condition. In contrast with earlier results, we do not require a positive lower bound for finite-system Hamiltonians uniform in the system size. To obtain this result, we adapt the Bravyi-Hastings-Michalakis strategy to the GNS representation of the infinite-system ground state.
Added Section 3.4 with an additional result; streamlined the exposition; updated references