24 research outputs found
Excitation basis for (3+1)d topological phases
We consider an exactly solvable model in 3+1 dimensions, based on a finite
group, which is a natural generalization of Kitaev's quantum double model. The
corresponding lattice Hamiltonian yields excitations located at
torus-boundaries. By cutting open the three-torus, we obtain a manifold bounded
by two tori which supports states satisfying a higher-dimensional version of
Ocneanu's tube algebra. This defines an algebraic structure extending the
Drinfel'd double. Its irreducible representations, labeled by two fluxes and
one charge, characterize the torus-excitations. The tensor product of such
representations is introduced in order to construct a basis for (3+1)d gauge
models which relies upon the fusion of the defect excitations. This basis is
defined on manifolds of the form , with a
two-dimensional Riemann surface. As such, our construction is closely related
to dimensional reduction from (3+1)d to (2+1)d topological orders.Comment: 33 pages; v2 references added; v3 minor change
Towards a dual spin network basis for (3+1)d lattice gauge theories and topological phases
Using a recent strategy to encode the space of flat connections on a
three-manifold with string-like defects into the space of flat connections on a
so-called 2d Heegaard surface, we propose a novel way to define gauge invariant
bases for (3+1)d lattice gauge theories and gauge models of topological phases.
In particular, this method reconstructs the spin network basis and yields a
novel dual spin network basis. While the spin network basis allows to interpret
states in terms of electric excitations, on top of a vacuum sharply peaked on a
vanishing electric field, the dual spin network basis describes magnetic (or
curvature) excitations, on top of a vacuum sharply peaked on a vanishing
magnetic field (or flat connection). This technique is also applicable for
manifolds with boundaries. We distinguish in particular a dual pair of boundary
conditions, namely of electric type and of magnetic type. This can be used to
consider a generalization of Ocneanu's tube algebra in order to reveal the
algebraic structure of the excitations associated with certain 3d manifolds.Comment: 45 page
Tube algebras, excitations statistics and compactification in gauge models of topological phases
We consider lattice Hamiltonian realizations of (+1)-dimensional
Dijkgraaf-Witten theory. In (2+1)d, it is well-known that the Hamiltonian
yields point-like excitations classified by irreducible representations of the
twisted quantum double. This can be confirmed using a tube algebra approach. In
this paper, we propose a generalization of this strategy that is valid in any
dimensions. We then apply the tube algebra approach to derive the algebraic
structure of loop-like excitations in (3+1)d, namely the twisted quantum
triple. The irreducible representations of the twisted quantum triple algebra
correspond to the simple loop-like excitations of the model. Similarly to its
(2+1)d counterpart, the twisted quantum triple comes equipped with a compatible
comultiplication map and an -matrix that encode the fusion and the braiding
statistics of the loop-like excitations, respectively. Moreover, we explain
using the language of loop-groupoids how a model defined on a manifold that is
-times compactified can be expressed in terms of another model in -lower
dimensions. This can in turn be used to recast higher-dimensional tube algebras
in terms of lower dimensional analogues.Comment: 71 page
On 2-form gauge models of topological phases
We explore various aspects of 2-form topological gauge theories in (3+1)d.
These theories can be constructed as sigma models with target space the second
classifying space of the symmetry group , and they are classified by
cohomology classes of . Discrete topological gauge theories can typically
be embedded into continuous quantum field theories. In the 2-form case, the
continuous theory is shown to be a strict 2-group gauge theory. This embedding
is studied by carefully constructing the space of -form connections using
the technology of Deligne-Beilinson cohomology. The same techniques can then be
used to study more general models built from Postnikov towers. For finite
symmetry groups, 2-form topological theories have a natural lattice
interpretation, which we use to construct a lattice Hamiltonian model in (3+1)d
that is exactly solvable. This construction relies on the introduction of a
cohomology, dubbed 2-form cohomology, of algebraic cocycles that are identified
with the simplicial cocycles of as provided by the so-called
-construction of Eilenberg-MacLane spaces. We show algebraically and
geometrically how a 2-form 4-cocycle reduces to the associator and the braiding
isomorphisms of a premodular category of -graded vector spaces. This is used
to show the correspondence between our 2-form gauge model and the Walker-Wang
model.Comment: 78 page
Crossing with the circle in Dijkgraaf-Witten theory and applications to topological phases of matter
Given a fully extended topological quantum field theory, the 'crossing with
the circle' conditions establish that the dimension, or categorification
thereof, of the quantum invariant assigned to a closed -manifold is
equivalent to that assigned to the (+1)-manifold . We compute in this manuscript these conditions for the 4-3-2-1
Dijkgraaf-Witten theory. In the context of the lattice Hamiltonian realisation
of the theory, the quantum invariants assigned to the circle and the torus
encode the defect open string-like and bulk loop-like excitations,
respectively. The corresponding 'crossing with the circle' condition thus
formalises the process by which loop-like excitations are formed out of
string-like ones. Exploiting this result, we revisit the statement that
loop-like excitations define representations of the linear necklace group as
well as the loop braid group
Computing the renormalization group flow of two-dimensional theory with tensor networks
We study the renormalization group flow of theory in two dimensions.
Regularizing space into a fine-grained lattice and discretizing the scalar
field in a controlled way, we rewrite the partition function of the theory as a
tensor network. Combining local truncations and a standard coarse-graining
scheme, we obtain the renormalization group flow of the theory as a map in a
space of tensors. Aside from qualitative insights, we verify the scaling
dimensions at criticality and extrapolate the critical coupling constant
to the continuum to find , which favorably compares with alternative methods
From gauge to higher gauge models of topological phases
We consider exactly solvable models in (3+1)d whose ground states are
described by topological lattice gauge theories. Using simplicial arguments, we
emphasize how the consistency condition of the unitary map performing a local
change of triangulation is equivalent to the coherence relation of the
pentagonator 2-morphism of a monoidal 2-category. By weakening some axioms of
such 2-category, we obtain a cohomological model whose underlying 1-category is
a 2-group. Topological models from 2-groups together with their lattice
realization are then studied from a higher gauge theory point of view. Symmetry
protected topological phases protected by higher symmetry structures are
explicitly constructed, and the gauging procedure which yields the
corresponding topological gauge theories is discussed in detail. We finally
study the correspondence between symmetry protected topological phases and 't
Hooft anomalies in the context of these higher group symmetries.Comment: 38 pages, v2: minor revisio
Dualities in one-dimensional quantum lattice models: topological sectors
It has been a long-standing open problem to construct a general framework for
relating the spectra of dual theories to each other. Building on ref.
[arXiv:2112.09091], whereby dualities are defined between (categorically)
symmetric models that only differ in a choice of module category, we solve this
problem for the case of one-dimensional quantum lattice models with
symmetry-twisted boundary conditions. Using matrix product operators, we
construct from the data of module functors explicit symmetry operators
preserving boundary conditions as well as intertwiners mapping topological
sectors of dual models onto one another. We illustrate our construction with a
family of examples that are in the duality class of the spin-
Heisenberg XXZ model. One model has symmetry operators forming the fusion
category of representations of the group . We find that the mapping between its topological sectors and those of the
XXZ model is associated with the non-trivial braided auto-equivalence of the
Drinfel'd center of .Comment: 24+7 page