Tunneling Topological Vacua via Extended Operators: (Spin-)TQFT Spectra and Boundary Deconfinement in Various Dimensions

Jan 16, 2018
52 pages
Published in:
  • PTEP 2018 (2018) 5, 053A01
  • Published: May 1, 2018
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Abstract: (Oxford University Press)
Distinct quantum vacua of topologically ordered states can be tunneled into each other via extended operators. The possible applications include condensed matter and quantum cosmology. We present a straightforward approach to calculate the partition function on various manifolds and ground state degeneracy (GSD), mainly based on continuum/cochain topological quantum field theories (TQFTs), in any dimension. This information can be related to the counting of extended operators of bosonic/fermionic TQFTs. On the lattice scale, anyonic particles/strings live at the ends of line/surface operators. Certain systems in different dimensions are related to each other through dimensional reduction schemes, analogous to (de)categorification. Examples include spin TQFTs derived from gauging the interacting fermionic symmetry-protected topological states (with fermion parity Z2f\mathbb{Z}_2^f) of symmetry groups Z4×Z2\mathbb{Z}_4\times \mathbb{Z}_2 and (Z4)2(\mathbb{Z}_4)^2 in 3+1D, also Z2\mathbb{Z}_2 and (Z2)2(\mathbb{Z}_2)^2 in 2+1D. Gauging the last three cases begets non-Abelian spin TQFTs (fermionic topological order). We consider situations where a TQFT lives on (1) a closed spacetime or (2) a spacetime with a boundary, such that the bulk and boundary are fully gapped and short- or long-range entangled (SRE/LRE). Anyonic excitations can be deconfined on the boundary. We introduce new exotic topological interfaces on which neither particle nor string excitations alone condense, but only fuzzy-composite objects of extended operators can end (e.g., a string-like composite object formed by a set of particles can end on a special 2+1D boundary of 3+1D bulk). We explore the relations between group extension constructions and partially breaking constructions (e.g., 0-form/higher-form/“composite” breaking) of topological boundaries, after gauging. We comment on the implications of entanglement entropy for some such LRE systems
Note:
  • 59 pages, 8 figures, 7 tables. v3: Elaborate spin TQFTs and fermionic topological orders (3+1D/2+1D) derived from Cobordism classifications of fermionic SPTs. More clarifications/Refs added. PTEP version
  • A13 Other topics in mathematical physics
  • A63 Quantum many-body systems
  • B00 Lattice gauge field theories
  • B37 Various models of field theory
  • I46 Strong correlations
  • field theory: topological
  • vacuum state: topological
  • operator: surface
  • boson: operator
  • string: excited state