Welcome to the Modular-qudit Kingdom.

Three qutrit code[1] A \([[3,1,2]]_3\) prime-qudit CSS code with stabilizer generators \(ZZZ\) and \(XXX\). The code defines a quantum secret-sharing scheme and serves as a minimal model for the AdS/CFT holographic duality. It is also the smallest non-trivial instance of a quantum maximum distance separable code (QMDS), saturating the quantum Singleton bound. The codewords are \begin{align} \begin{split} | \overline{0} \rangle &= \frac{1}{\sqrt{3}} (| 000 \rangle + | 111 \rangle + | 222 \rangle) \\ | \overline{1} \rangle &= \frac{1}{\sqrt{3}} (| 012 \rangle + | 120 \rangle + | 201 \rangle) \\ | \overline{2} \rangle &= \frac{1}{\sqrt{3}} (| 021 \rangle + | 102 \rangle + | 210 \rangle)~. \end{split} \end{align} The elements in the superposition of each logical codeword are related to each other via cyclic permutations. Protection: Detects single qutrit errors and protects against a single-qutrit erasure. There does not exist a three-qubit code with analogous properties. Parents: Modular-qudit CSS code, Holographic code, Quantum maximum-distance-separable (MDS) code. Cousins: Approximate secret-sharing code. Cousin of: \([[3,1,2]]_{\mathbb Z}\) rotor code.
Modular-qudit code Also called a \(\mathbb{Z}_q\)-qudit code. Encodes \(K\)-dimensional Hilbert space into a \(q^n\)-dimensional (\(n\)-qudit) Hilbert space, with canonical qudit states \(|k\rangle\) labeled by elements \(k\) of the group \(\mathbb{Z}_q\) of integers modulo \(q\). Usually denoted as \(((n,K))_q\) or \(((n,K,d))_q\), whenever the code's distance \(d\) is defined, and with \(q=p\) when the dimension is prime. Protection: A convenient and often considered error set is the modular-qudit analogue of the Pauli string basis for qubit codes. For a single qudit, this set consists of products of powers of the qudit Pauli matrices \(X\) and \(Z\), which act on computational basis states \(|k\rangle\) for \(k\in\mathbb{Z}_q\) as \begin{align} X\left|k\right\rangle =\left|k+1\right\rangle \,\,\text{ and }\,\,Z\left|k\right\rangle =e^{i\frac{2\pi}{q}k}\left|k\right\rangle ~, \end{align} with addition performed modulo \(q\). For multiple qudits, error set elements are tensor products of elements of the single-qudit error set. Parents: Finite-dimensional quantum error-correcting code. Parent of: Modular-qudit stabilizer code. Cousin of: Entanglement-assisted (EA) QECC, Galois-qudit code, Group-based quantum code.
Modular-qudit stabilizer code[2] An \(((n,K,d))_q\) modular-qudit code whose logical subspace is the joint eigenspace of commuting 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 qudit Pauli string that implements a nontrivial logical operation in the code. Protection: Detects errors on up to \(d-1\) qudits, and corrects erasure errors on up to \(d-1\) qudits. More generally, define the normalizer \(\mathsf{N(S)}\) of \(\mathsf{S}\) to be the set of all operators that commute with all \(S\in\mathsf{S}\). A stabilizer code can correct a Pauli error set \({\mathcal{E}}\) if and only if \(E^\dagger F \notin \mathsf{N(S)}\setminus \mathsf{S}\) for all \(E,F \in {\mathcal{E}}\). Parents: Stabilizer code, Modular-qudit code, Quantum Lego code. Parent of: Double-semion code, Frobenius code, Modular-qudit CSS code. Cousin of: Abelian topological code, Galois-qudit stabilizer code, Qubit stabilizer code, Subsystem modular-qudit stabilizer code, Translationally-invariant stabilizer code.
Frobenius code[4] Let \(C\) be a quantum cyclic code on \(n\) prime-dimensional qudits. \(C\) is a Frobenius code if there exists a positive integer \(t\) such that \(n\) divides \(p^t +1\). Protection: Protects against Pauli noise. Parents: Modular-qudit stabilizer code, Quantum cyclic code.
Modular-qudit CSS code[5][6][7] An \(((n,K,d))_q\) modular-qudit stabilizer code admitting a set of stabilizer generators that are either \(Z\)-type or \(X\)-type Pauli strings. The stabilizer generator matrix, taking values from \(\mathbb{Z}_q\), is of the form \begin{align} H=\begin{pmatrix}0 & H_{Z}\\ H_{X} & 0 \end{pmatrix} \label{eq:parityq} \end{align} such that the rows of the two blocks must be orthogonal \begin{align} H_X H_Z^T=0~. \label{eq:commQ} \end{align} The above condition guarantees that the \(X\)-stabilizer generators, defined in the symplectic representation as rows of \(H_X\), commute with the \(Z\)-stabilizer generators associated with \(H_Z\). Parents: Modular-qudit stabilizer code. Parent of: Modular-qudit surface code, Quantum Reed-Solomon code, Three qutrit code, \([[2^r-1, 2^r-2r-1, 3]]_p\) prime-qudit CSS code. Cousins: Calderbank-Shor-Steane (CSS) stabilizer code, Linear \(q\)-ary code. Cousin of: Group GKP code.
Modular-qudit surface code[8][9][10] Extension of the surface code to prime-dimensional [8][9] and more general modular qudits [10]. Stabilizer generators are few-body \(X\)-type and \(Z\)-type Pauli strings associated to the stars and plaquettes, respectively, of a tessellation of a two-dimensional surface. Since qudits have more than one \(X\) and \(Z\)-type operator, various sets of stabilizer generators can be defined. Ground-state degeneracy and the associated phase depends on the qudit dimension and the stabilizer generators. Parents: Modular-qudit CSS code. Cousins: Abelian topological code, Kitaev surface code, String-net code. Cousin of: Quantum-double code, Translationally-invariant stabilizer code.
Quantum Reed-Solomon code[11] Also called prime-qudit polynomial code (QPyC). Prime-qudit CSS code constructed using two Reed-Solomon codes. Parents: Modular-qudit CSS code. Cousins: Reed-Solomon (RS) code, Quantum maximum-distance-separable (MDS) code. Cousin of: Galois-qudit RS code.
\([[2^r-1, 2^r-2r-1, 3]]_p\) prime-qudit CSS code[12] A family of CSS codes extending Hamming-based CSS codes to prime qudits of dimension \(p\) by expressing the qubit code stabilizers in local-dimension-invariant (LDI) form [12]. Parents: Modular-qudit CSS code. Cousins: \([[2^r-1, 2^r-2r-1, 3]]\) Hamming-based CSS code.


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