Condensed Matter Physics and Topological Field Theory

Unitary fusion categories are the algebraic input for the Turaev-Viro (TV) type TQFTs in (2+1)-dimensions and their Hamiltonian realization for the Levin-Wen model. We are interested in a generalization to unitary 2-fusion category for (3+1)-dimensions. Mackaay's spherical 2-categories are not general enough to include interesting examples such as the G-crossed braided fusion categories and general homotopy 2-types. We will discussion new (3+1)-TQFTs with G-crossed braided fusion categories as input, and their lattice realization based on the thesis work of Shawn X. Cui.

Symmetry protected topological(SPT) phase is a generalization of topological insulator(TI). Different from the intrinsic topological phase, e.g., the fractional quantum hall(FQH) phase, SPT phase is only distinguishable from a trivial disordered phase when certain symmetry is preserved. Indeed, SPT phase has a long history in 1D, and it has been shown that the well known Haldane phase of S=1 Heisenberg chain belongs to this class. However, in higher dimensions, most of the previous studies focus on free electron systems. Until very recently, it was realized that SPT phase also exists in interacting boson/spin systems in higher dimensions. In this talk, I will discuss the general mechanism for bosonic SPT phases and propose a corresponding topological quantum field theory(TQFT)descriptions. I will focus on examples in three (spacial) dimensions, including bosonic topological insulators(BTI) .