## Description

Code whose codewords realize topological order associated with an Abelian anyon theory, equivalently, a unitary braided fusion category which is also an Abelian group under fusion [1].

A theory is defined by an Abelian group \(A\) of anyon types whose multiplication relations define the fusion rules, and a set of exchange statistics \(\theta(a)\in U(1)\) obtained by exchanging two anyons of type \(a\in A\). The exchange statistics in turn define braiding relations, \begin{align} B(a,b) = \frac{\theta(ab)}{\theta(a)\theta(b)}~, \tag*{(1)}\end{align} between all anyon pairs \(a,b\).

All 2D abelian topological orders can be understood within the subsystem stabilizer formalism [2]. As such, many of the operations one can perform on such codes have both a stabilizer and a topological-phase interpretation. Stabilizer generators of 2D topological codes acting on 1D loops of qubits can be interpreted as one-form symmetries of the underlying phase realized by the code. Identification of an anyon \(a\) with the vacuum is equivalent to adding string excitation operators corresponding to \(a\) to the stabilizer group and taking the center to get another stabilizer group. Code states of this new stabilizer code correspond to a condensed phase of the parent topological phase. The remaining unidentified parent-phase anyons behave differently with respect to the new condensed-phase state. Some become confined while the remaining ones pick up new braiding relations.

## Protection

## Encoding

## Gates

## Fault Tolerance

## Code Capacity Threshold

## Parents

- Subsystem modular-qudit stabilizer code — All Abelian topological orders can be realized as modular-qudit subsystem stabilizer codes by starting with an abelian quantum double model (slightly different from that of Ref. [21]) along with a family of Abelian TQDs that generalize the double semion anyon theory and gauging out certain bosonic anyons [2]. The stabilizer generators of the new subsystem code may no longer be geometrically local.
- Topological code — All Abelian topological orders can be realized as modular-qudit subsystem stabilizer codes [2]. Nonabelian topological orders are purported not to be realizable with Pauli stabilizer codes [22].

## Children

- Tetron Majorana code — When treated as ground states of the code Hamiltonian, surface codewords realize, codewords of a single Kitaev chain realize \(\mathbb{Z}_2\) fermionic topological order. The MZMs used to define the tetron code act as Ising anyons, which are nonabelian.
- Three-fermion (3F) model code — When treated as ground states of the code Hamiltonian, 3F model code states realize 3F topological order, which is chiral and modular.
- Three-fermion (3F) subsystem code — The 3F code is a subsystme code characterized by 3F topological order [2], which is chiral and modular.
- \(\mathbb{Z}_q^{(1)}\) subsystem code — The \(\mathbb{Z}_q^{(1)}\) subsystem code is characterized by the \(\mathbb{Z}_q^{(1)}\) anyon theory [23]. The anyon theory has a single generator \(a \in \mathbb Z_N\) with \(\theta(a) =e^{\frac{2\pi i}{N}a^2}\). It is modular for odd prime \(q\) and non-modular otherwise.
- Chiral semion subsystem code — The semion code is a subsystem code characterized by the chiral semion topological phase.
- \(\mathbb{Z}_3\times\mathbb{Z}_9\)-fusion subsystem code — The \(\mathbb{Z}_q^{(1)}\) subsystem code is characterized by a non-modular anyon theory with \(\mathbb{Z}_3\times\mathbb{Z}_9\) fusion rules.
- Abelian TQD stabilizer code — Abelian TQDs realize all modular gapped Abelian topological orders [21]. Conversely, every abelian anyon theory is a subtheory of some TQD [2; Sec. 6.2]. Any abelian anyon theory \(A\) can be realized at one of the surfaces of a 3D Walker-Wang model whose underlying theory is an abelian TQD containing \(A\) as a subtheory [24,25][2; Appx. H].

## Cousins

- Hamiltonian-based code — Subsystem stabilizer code Hamiltonians described by an Abelian anyon theory do not always realize the corresponding anyonic topological order in their ground-state subspace and may exhibit a rich phase diagram. For example, the Kitaev honeycomb Hamiltonian admits the anyon theories of the 16-fold way, i.e., all minimal modular extensions of the \(\mathbb{Z}_2^{(1)}\) abelian non-chiral non-modular anyon theory [26][2; Footnote 25].
- Walker-Wang model code — Any abelian anyon theory \(A\) can be realized at one of the surfaces of a 3D Walker-Wang model whose underlying theory is an abelian TQD containing \(A\) as a subtheory [24,25][2; Appx. H].
- Analog surface code — The analog surface code realizes a straightforward extension of the modular-qudit surface code to infinite local dimension, \(q\to\infty\). There are two types of anyons, \(e\) and \(m\), with each type being valued in \(U(1)\) as opposed to \(\mathbb{Z}_q\) for the qudit surface code.
- Dynamical automorphism (DA) code — Useful measurement sequences of DA Floquet codes can be extracted from topological quantum field theory [27].

## References

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- [18]
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- [20]
- C. T. Chubb and S. T. Flammia, “Statistical mechanical models for quantum codes with correlated noise”, Annales de l’Institut Henri Poincaré D 8, 269 (2021) arXiv:1809.10704 DOI
- [21]
- T. D. Ellison et al., “Pauli Stabilizer Models of Twisted Quantum Doubles”, PRX Quantum 3, (2022) arXiv:2112.11394 DOI
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- [23]
- P. H. Bonderson, Non-Abelian Anyons and Interferometry, California Institute of Technology, 2007 DOI
- [24]
- J. Haah, “Clifford quantum cellular automata: Trivial group in 2D and Witt group in 3D”, Journal of Mathematical Physics 62, 092202 (2021) arXiv:1907.02075 DOI
- [25]
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- [27]
- M. Davydova et al., “Quantum computation from dynamic automorphism codes”, (2023) arXiv:2307.10353

## Page edit log

- Victor V. Albert (2022-02-08) — most recent

## Cite as:

“Abelian topological code”, The Error Correction Zoo (V. V. Albert & P. Faist, eds.), 2022. https://errorcorrectionzoo.org/c/topological_abelian