Universal Wave Function Overlap and Universal Topological Data from   Generic Gapped Ground States
  We propose a way -- universal wave function overlap -- to extract universal topological data from generic ground states of gapped systems in any dimensions. Those extracted topological data should fully characterize the topological orders with gapped or gapless boundary. For non-chiral topological orders in 2+1D, this universal topological data consist of two matrices, $S$ and $T$, which generate a projective representation of $SL(2,\mathbb Z)$ on the degenerate ground state Hilbert space on a torus. For topological orders with gapped boundary in higher dimensions, this data constitutes a projective representation of the mapping class group $MCG(M^d)$ of closed spatial manifold $M^d$. For a set of simple models and perturbations in two dimensions, we show that these quantities are protected to all orders in perturbation theory. 
Heidar Moradi, Xiao-Gang Wen
cond-mat.str-el