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arXiv:2610.36029

AlgebrasTQD: Computing Algebras and Interfaces in Twisted Quantum Doubles

Alison Warman

cond-mat.str-elhep-thmath.QAquant-phSubmitted Oct 26, 2026• Announced Oct 28, 2026• 0 citations
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Abstract

We present AlgebrasTQD, an open-source code written in GAP (Groups, Algorithms, and Programming), for computing condensable algebras and the corresponding topological boundaries and interfaces of twisted quantum doubles $D^ω(G)$. These algebras can be used to classify 1+1d gapped and gapless phases whose symmetry is related by gauging to a finite group $G$ with anomaly $ω\in H^3(G,U(1))$, to study 2+1d anyon proliferation and to construct logical gates in non-Abelian topological quantum codes. The functions in AlgebrasTQD compute all condensable algebras $A(H,F,γ,ε)$ with their algebra structure and anyons, sort them into isomorphism classes and identify the twin algebras that are inequivalent but share the same anyon decomposition. AlgebrasTQD also determines all the subalgebra relations, the corresponding Hasse diagram and the types of 1+1d phases for any chosen, possibly non-invertible, group-theoretical symmetry. For non-maximal algebras, the code computes the reduced topological order with its $3$-cocycle and the map of anyons across the topological interface. Finally, AlgebrasTQD includes functions that construct certain non-Clifford logical gates via non-Abelian surface codes. We summarize the formulas that are implemented in the AlgebrasTQD code, and we illustrate its use with Abelian and non-Abelian groups including $\mathbb{Z}_2^3$ with $ω_\text{III}$, $D_8$, $A_4$ with and without anomaly, twin algebras and twin phases, and the Clifford-hierarchy gates in quantum doubles of dihedral groups. All arithmetic is exact and AlgebrasTQD can be used with any finite group $G$ and 3-cocycle $ω$, limited only by the time and size of the calculation. The code is available at https://github.com/AlisonWarman/AlgebrasTQD

Comments
38 pages, companion paper to the code at https://github.com/AlisonWarman/AlgebrasTQD

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We present AlgebrasTQD, an open-source code written in GAP (Groups, Algorithms, and Programming), for computing condensable algebras and the corresponding topological boundaries and interfaces of twisted quantum doubles Dω(G)D^ω(G)Dω(G). These algebras can be used to classify 1+1d gapped and gapless phases whose symmetry is related by gauging to a finite group GGG with anomaly ω∈H3(G,U(1))ω\in H^3(G,U(1))ω∈H3(G,U(1)), to study 2+1d anyon proliferation and to construct logical gates in non-Abelian topological quantum codes. The functions in AlgebrasTQD compute all condensable algebras A(H,F,γ,ε)A(H,F,γ,ε)A(H,F,γ,ε) with their algebra structure and anyons, sort them into isomorphism classes and identify the twin algebras that are inequivalent but share the same anyon decomposition. AlgebrasTQD also determines all the subalgebra relations, the corresponding Hasse diagram and the types of 1+1d phases for any chosen, possibly non-invertible, group-theoretical symmetry. For non-maximal algebras, the code computes the reduced topological order with its 333-cocycle and the map of anyons across the topological interface. Finally, AlgebrasTQD includes functions that construct certain non-Clifford logical gates via non-Abelian surface codes. We summarize the formulas that are implemented in the AlgebrasTQD code, and we illustrate its use with Abelian and non-Abelian groups including Z23\mathbb{Z}_2^3Z23​ with ωIIIω_\text{III}ωIII​, D8D_8D8​, A4A_4A4​ with and without anomaly, twin algebras and twin phases, and the Clifford-hierarchy gates in quantum doubles of dihedral groups. All arithmetic is exact and AlgebrasTQD can be used with any finite group GGG and 3-cocycle ωωω, limited only by the time and size of the calculation. The code is available at https://github.com/AlisonWarman/AlgebrasTQD
Condensable algebras in 2+1d non-chiral topological orders characterize gapped boundary conditions and interfaces. Applied to the Symmetry Topological Field Theory, they allow classification of symmetric gapped phases and impose sharp constraints on possible phase transitions. A condensable algebra is specified not only by its underlying set of anyons, which end on the boundary or interface, but also by its algebra structure. We introduce the concept of twin condensable algebras, which have the same anyon decomposition, but inequivalent algebra structure. We revisit the classification of condensable algebras in Z(VecGω)\mathcal{Z}(\text{Vec}_G^ω)Z(VecGω​), i.e. in group-theoretical topological orders for finite groups GGG with anomaly ωωω. In this context we are able to identify twin algebras that arise from different mechanisms, such as subgroup data, SPT cocycles, and symmetry actions. In particular, we construct infinite families of examples of twins from so-called Gassmann triples, and exhibit cases in which the reduced topological orders are inequivalent despite having identical anyon content. Physically, twin algebras describe distinct symmetric phases that have isomorphic spaces of ground states, but inequivalent order parameters. Such twin phases never exhibit relative spontaneous symmetry breaking, and can be used to construct phase transitions without hidden symmetry breaking, which are intrinsically beyond Landau transitions.
Proliferation transitions are phase transitions between a 2+1d topological order T\mathcal{T}T and another T/A\mathcal{T}/\mathcal{A}T/A, obtained by condensing anyons in an algebra A⊂T\mathcal{A}\subset \mathcal{T}A⊂T. We consider such transitions in quantum doubles of groups, T=D(G,ω)\mathcal{T}=D(G, ω)T=D(G,ω), for finite groups GGG possibly with three-cocycle ωωω, for which condensable algebras are fully classified. Given a condensable algebra A\mathcal{A}A, we represent T\mathcal{T}T in terms of a Symmetry Topological Field Theory (SymTFT), that is tailored to the A\mathcal{A}A proliferation transition. The SymTFT bulk is constructed from the Müger center of the subcategory generated by the algebra, i.e. the category of transparent lines, which can be bosons or fermions. Properties of the transition can then be inferred directly from the algebra classification data. For gauged Landau-Ginzburg (LG*) type transitions, we show that they do not only depend on the anyons in A\mathcal{A}A through their field content, but the cubic interactions are fixed in terms of the multiplication structure of A\mathcal{A}A. Applied to twin algebras, which have the same anyon content but different multiplication structures, we show that twins result in distinct proliferation transitions.
A fundamental problem in fault-tolerant quantum computation is the tradeoff between universality and dimensionality, exemplified by the the Bravyi-König bound for nnn-dimensional topological stabilizer codes. In this work, we extend topological Pauli stabilizer codes to a broad class of nnn-dimensional Clifford hierarchy stabilizer codes. These codes correspond to the (n+1)(n+1)(n+1)D Dijkgraaf-Witten gauge theories with non-Abelian topological order. We construct transversal non-Clifford gates through automorphism symmetries represented by cup products. In 2D, we obtain the first transversal non-Clifford logical gates including T and CS for Clifford stabilizer codes, using the automorphism of the twisted Z23\mathbb{Z}_2^3Z23​ gauge theory (equivalent to D4\mathbb{D}_4D4​ topological order). We also combine it with the just-in-time decoder to fault-tolerantly prepare the logical T magic state in O(d)O(d)O(d) rounds via code switching. In 3D, we construct a transversal logical T\sqrt{\text{T}}T​ gate in a non-Clifford stabilizer code at the third level of the Clifford hierarchy, located on a tetrahedron corresponding to a twisted Z24\mathbb{Z}_2^4Z24​ gauge theory. Our constructions surpass the Bravyi-König bound by achieving the logical gates in the (n+1)(n+1)(n+1)-th level of Clifford hierarchy in nnn spatial dimension.
We construct a Pauli stabilizer model for every two-dimensional Abelian topological order that admits a gapped boundary.Our primary example is a Pauli stabilizer model on four-dimensional qudits that belongs to the double semion (DS) phase of matter.The DS stabilizer Hamiltonian is constructed by condensing an emergent boson in a Z 4 toric code, where the condensation is implemented at the level of the ground states by two-body measurements.We rigorously verify the topological order of the DS stabilizer model by identifying an explicit finite-depth quantum circuit (with ancillary qubits) that maps its ground-state subspace to that of a DS string-net model.We show that the construction of the DS stabilizer Hamiltonian generalizes to all twisted quantum doubles (TQDs) with Abelian anyons.This yields a Pauli stabilizer code on composite-dimensional qudits for each such TQD, implying that the classification of topological Pauli stabilizer codes extends well beyond stacks of toric codes-in fact, exhausting all Abelian anyon theories that admit a gapped boundary.We also demonstrate that symmetry-protected topological phases of matter characterized by type-I and type-II cocycles can be modeled by Pauli stabilizer Hamiltonians by gauging certain 1-form symmetries of the TQD stabilizer models.
Recent work has shown that quantum double models can be used to circumvent the Bravyi-Koenig bound. In particular, this is achieved through code-switching protocols in which non-Pauli stabilizer phases appear as intermediate codes. We introduce the XCd(k)X\mathcal C^{(k)}_dXCd(k)​ stabilizer formalism, which generalizes the Pauli stabilizer formalism by combining Pauli-XXX operators with diagonal operators drawn from a fixed level kkk of the Clifford hierarchy on prime-dimensional qudits. This yields a natural class of beyond-Pauli stabilizer models, including many twisted quantum double phases. We classify a large class of these XCd(k)X\mathcal C^{(k)}_dXCd(k)​ stabilizer states, showing that they are uniform superpositions over affine-linear subspaces with diagonal phases. In particular, when the stabilizers of a state require operators from level kkk of the Clifford hierarchy, we show that the diagonal gates required to produce the phases in the wavefunction sit one level higher. We further show that every 2D twisted quantum double Dω(Zpn){\cal D}^ω(\mathbb{Z}_p^n)Dω(Zpn​) with ωωω a product of type-III cocycles and ppp an odd prime admits a realization using only Clifford (k=2k=2k=2) stabilizers, and we conjecture that phases where ωωω contains a type-I or type-II cocycle require level-ppp Clifford-hierarchy stabilizers for ppp-dimensional qudits. Finally, we demonstrate that a pair of qudit toric codes may be deterministically prepared in a logical magic state by measuring XCd(k)X\mathcal C^{(k)}_dXCd(k)​ stabilizers. Together, these results provide a concrete stabilizer framework for topological codes beyond Pauli stabilizer models and their logical gates.
Self-dual S3S_3S3​ gauge theory in 2+1d: lattice model and topological phase transitions
Electric-magnetic self-duality of the Z2\mathbb{Z}_2Z2​ gauge theory, realized microscopically as a half-lattice-translation exchanging electric charge and magnetic flux, has been an influential example of a duality symmetry with an exact lattice realization. We construct the first non-Abelian generalization of this construction: a lattice model of the S3S_3S3​ quantum double D(S3)\mathcal{D}(S_3)D(S3​) on a tensor product Hilbert space in which the Z2em\mathbb{Z}^{\mathrm{em}}_2Z2em​ anyon-permutation symmetry, exchanging the non-Abelian chargeon CCC and fluxon FFF, is realized via lattice translation. Consequently we find that the zigzag boundary termination of the model realizes, without fine-tuning, a gapless critical edge state described by the tetracritical Ising CFT. The bulk admits three independent Z2em\mathbb{Z}_2^{\mathrm{em}}Z2em​-preserving bosonic perturbations, driving D(S3)\mathcal{D}(S_3)D(S3​) into distinct gapped phases. We analyze these transitions by three independent methods: category-theoretic anyon condensation, microscopic lattice Hamiltonians, and Chern-Simons-Higgs theory, which all agree, yielding a unified picture. These examples motivate a minimal-condensation principle: proliferating a bosonic anyon generically drives condensation of a minimal condensable algebra containing it, with symmetry-related condensates appearing as degenerate vacua that spontaneously break the anyon-permutation symmetry. Our model construction extends to an infinite family of self-dual dihedral quantum doubles D(D2n)\mathcal{D}(D_{2n})D(D2n​). Notably, each model is sign-problem-free, opening the door to large-scale numerical exploration of the phases of non-Abelian Chern-Simons-Higgs theories.