In 1997, Shor and Laflamme defined the weight enumerators for quantum error-correcting codes and derived a MacWilliams identity. We extend their work by introducing our double weight enumerators and complete weight enumerators for qubit codes and then investigate the MacWilliams identities for these enumerators. Based on the generalized MacWilliams identities, we solve an open problem, namely, the Singleton-type bound for asymmetric quantum codes (AQCs). Besides, the Hamming-type and the first linear-programming-type bounds for the AQCs are deduced similarly.
This paper develops a MacWilliams-type enumerator theory and semidefinite programming bounds for intrinsic quantum codes. An intrinsic code is a subspace
C⊂V of a finite-dimensional unitary representation
V of a group
G, with errors organized into the isotypic components of
L(V) under conjugation. The Knill-Laflamme conditions persist under every
G-equivariant realization of
V, aallowing intrinsic bounds to apply across diverse physical encodings. Without a group action, we first construct projector and twirl quadratic enumerators for an arbitrary orthogonal decomposition of
L(V), analogous respectively to the
A and
B enumerators of Shor-Laflamme theory. These enumerators satisfy positivity, normalization, and Knill-Laflamme inequalities, but the two superoperator families need not span the same space and therefore admit no canonical duality. A group action places their generalized versions in the same equivariant intertwiner algebra, and the change of basis between them defines the intrinsic MacWilliams transform. When the conjugation representation has multiplicities, this algebra is noncommutative and the enumerators are matrix-valued; positivity and detection are encoded by Loewner-order constraints, making the natural programming bound a semidefinite program. The multiplicity-free specialization recovers the known scalar MacWilliams transform and linear-programming framework. For symmetric powers, intrinsic depth equals ordinary qudit distance, yielding extremality certificates for permutation-invariant qudit codes. Finally, for the
27-dimensional
SU(3) representation
V=(2,2), an exact dual certificate proves the sharp bound
K≤5 for codes detecting the full adjoint isotypic component. An explicit
5-dimensional code attains the bound and, under the canonical embedding, gives a four-qutrit distance-
2 code.
As emerging quantum architectures evolve into heterogeneous networks combining different physical substrates, such as qubits for logic and higher-dimensional qudits for robust communication, the traditional scalar metrics of quantum error correction become insufficient. To address this, we introduce a mathematical framework based on dimension multisets to characterize quantum error-correcting codes (QECC) and absolutely maximally entangled (AME) states in mixed-dimensional Hilbert spaces. By replacing scalar weights with multisets, we accurately capture the exact physical composition of error supports across these diverse systems. Our central result is the mixed-dimensional quantum MacWilliams identity, which establishes the formal algebraic relationship between Shor-Laflamme enumerators and unitary weight enumerators. From this foundation, we deduce the mixed-dimensional shadow identity and derive rigorous, generalized constraints on code parameters, explicitly formulating the mixed-dimensional quantum Hamming, Singleton and Scott bounds, and developing a linear program to systematically evaluate code viability. For the Singleton bound, a tighter bound that has no homogeneous analogue is derived for pure mixed-dimensional codes. Finally, we deploy this enumerator machinery to thoroughly analyze AME states, utilizing shadow inequalities to constrain their existence and introducing a combinatorial grid method for the explicit construction of mixed-dimensional tripartite AME states.
In a recent paper, Hu et al. defined the complete weight distributions of quantum codes and proved the MacWilliams identities, and as applications they showed how such weight distributions may be used to obtain the singleton-type and hamming-type bounds for asymmetric quantum codes. In this paper we extend their study much further and obtain several new results concerning the complete weight distributions of quantum codes and applications. In particular, we provide a new proof of the MacWilliams identities of the complete weight distributions of quantum codes. We obtain new information about the weight distributions of quantum MDS codes and the double weight distribution of asymmetric quantum MDS codes. We get new identities involving the complete weight distributions of two different quantum codes. We estimate the complete weight distributions of quantum codes under special conditions and show that quantum BCH codes by the Hermitian construction from primitive, narrow-sense BCH codes satisfy these conditions and hence these estimate applies.
A classical bit fails one way: it flips. A qubit fails three ways—X, Z, or both at once—and that single change of arithmetic, from one error per site to three, is the whole difference between the classical theory of error-correcting codes and the quantum one. It has a precise home. The MacWilliams identity of 1963 is the exact law relating a linear code's weight distribution to its dual's; its quantum analogue, due to Shor and Laflamme, carries the same law across the stabilizer formalism with one coefficient changed—a +1 becomes a +3. We prove that quantum identity in the kernel of a proof assistant, and we prove it the honest way: by reusing, unchanged, the finite character-orthogonality argument that certifies the classical identity, isolating the +3 to a single new lemma about the four Pauli operators at one qubit. The classical coefficient is not merely inapplicable to quantum codes; we exhibit a code on which the +1 law is false and its failure is itself a theorem. From the certified identity the entire Shor–Laflamme weight spectrum of a code follows—the count of stabilizers and of logical operators at every weight—and from the spectrum two numbers the field cares about: the code distance (the minimum weight of a logical operator, recovered as the first place the spectra part) and the sub-threshold error-rate prefactor (the count of minimum-weight logical representatives, which the distance alone cannot see). We certify both for the five-qubit perfect code and the Steane code, exhibit the exact spectra, and place the result beside a companion certificate that reaches the distance by a single witness: the witness is a local probe, the enumerator a global census, and a code is fully accounted for only when both have spoken. A public instrument reproduces every number by independent enumeration, trusting neither our kernel nor our word. Published by The Institute for Applied Ontological Mathematics.