## Description

An \(((n,K,d))_q\) Galois-qudit code whose logical subspace is the joint eigenspace of commuting Galois-qudit Pauli operators forming the code's stabilizer group \(\mathsf{S}\). Traditionally, the logical subspace is the joint \(+1\) eigenspace, and the stabilizer group does not contain \(e^{i \phi} I\) for any \(\phi \neq 0\). The distance \(d\) is the minimum weight of a Galois-qudit Pauli string that implements a nontrivial logical operation in the code.

A Galois-qudit stabilizer code encoding an integer number of qudits (\(K=q^k\)) is denoted as \([[n,k]]_q\) or \([[n,k,d]]_q\). This notation differentiates between Galois-qudit and modular-qudit \([[n,k,d]]_{\mathbb{Z}_q}\) stabilizer codes, although the same notation is usually used for both. Galois-qudit stabilizer codes need not encode an integer number of qudits, with \(K=q^{n-\frac{r}{m}}\), where \(r\) is the number of generators of the stabilizer group, and \(q=p^m\) given prime \(p\) for all Galois qudits. As a result, \([[n,k,d]]\) notation is often used with non-integer \(k=\log_q K\).

The stabilizer commutation condition can equivalently be stated in the symplectic representation. A pair of Galois-qudit stabilizers on \(n\) Galois qudits with symplectic representation vectors \((a|b)\) and \((a^{\prime}|b^{\prime})\) commute iff their trace symplectic inner product is zero, \begin{align} \text{tr}(a \cdot b^{\prime} - a^{\prime}\cdot b) = \sum_{j=1}^{n} \text{tr}(a_j b^{\prime}_j - a^{\prime}_i b_i) = 0~. \tag*{(1)}\end{align} Symplectic representations of stabilizer group elements thus form a self-orthogonal subspace of \(GF(q)^{2n}\) with respect to the trace-symplectic inner product.

Note that the above trace-symplectic inner product reduces to the symplectic inner product when the trace is removed, and a symplectic self-orthogonal set of vectors is automatically trace-symplectic self-orthogonal. More generally, any additive classical code whose self-orthogonality under some inner product (such as Hermitian, Euclidean, or symplectic) implies trace-symplectic self-orthogonality of an equivalent code can be used to construct a Galois-qudit stabilizer code (see children).

## Protection

## Encoding

## Gates

## Notes

## Parents

- Galois-qudit non-stabilizer code — A non-stabilizer code is also a stabilizer code if its Fourier description \(\mathsf{B}\) is a subgroup of some Gottesman subgroup \(\mathsf{S}\). When \(\mathsf{B}\) is just a subset, the code is explicitly not a stabilizer code.
- Stabilizer code

## Children

- Qubit stabilizer code — Galois-qudit stabilizer codes for \(q=2\) correspond to qubit stabilizer codes.
- True Galois-qudit stabilizer code
- Generalized homological product code

## Cousins

- Modular-qudit stabilizer code — Recalling that \(q=p^m\), Galois-qudit stabilizer codes can also be treated as prime-qudit stabilizer codes on \(mn\) qudits, giving \(k=nm-r\) [1]. The case \(m=1\) reduces to conventional prime-qudit stabilizer codes on \(n\) qudits.
- Additive \(q\)-ary code — Galois-qudit stabilizer codes are the closest quantum analogues of additive codes over \(GF(q)\) because addition in the field corresponds to multiplication of stabilizers in the quantum case.
- Dual additive code — An additive code of length \(2n\) over \(GF(q)\) that is self-orthogonal with respect to the trace-symplectic inner product corresponds to symplectic representations of an \(n\) Galois-qudit stabilizer group [1]. Moreover, any additive code whose self-orthogonality under some inner product (such as Hermitian, Euclidean, or symplectic) implies trace-symplectic self-orthogonality of an equivalent code can be used to construct a Galois-qudit stabilizer code.

## References

- [1]
- A. Ashikhmin and E. Knill, “Nonbinary quantum stabilizer codes”, IEEE Transactions on Information Theory 47, 3065 (2001) DOI
- [2]
- A. Ketkar et al., “Nonbinary stabilizer codes over finite fields”, (2005) arXiv:quant-ph/0508070
- [3]
- M. GRASSL, M. RÖTTELER, and T. BETH, “EFFICIENT QUANTUM CIRCUITS FOR NON-QUBIT QUANTUM ERROR-CORRECTING CODES”, International Journal of Foundations of Computer Science 14, 757 (2003) arXiv:quant-ph/0211014 DOI
- [4]
- D. Gross, “Hudson’s theorem for finite-dimensional quantum systems”, Journal of Mathematical Physics 47, 122107 (2006) arXiv:quant-ph/0602001 DOI

## Page edit log

- Victor V. Albert (2022-07-22) — most recent
- Victor V. Albert (2022-04-13)
- Leonid Pryadko (2022-04-13)
- Victor V. Albert (2022-01-12)
- Qingfeng (Kee) Wang (2022-01-07)

## Cite as:

“Galois-qudit stabilizer code”, The Error Correction Zoo (V. V. Albert & P. Faist, eds.), 2022. https://errorcorrectionzoo.org/c/galois_stabilizer