We demonstrate that absolutely maximally entangled (AME) states consisting of
N=4n qudits with
n∈{1,2,3,…}, each of even local dimension
d, cannot be realized as canonical graph states over the ring
Zd. This result imposes strong constraints on AME states in composite local dimensions and characterizes the limitations of graph-state constructions for highly entangled multipartite quantum systems. Furthermore, for
d≡2(mod4) this obstruction, combined with the prime-power decomposition of stabilizer states, excludes all pure stabilizer AME states (including four quhexes), while clarifying the distinction between canonical
Zd graph states and stabilizer constructions over prime-power factors. We also discuss a composite construction of mixed
k-uniform states. For
(N,d)=(4,6), the construction yields a rank-two mixed
2-uniform stabilizer state of purity
1/2, which is optimal among normalized stabilizer projectors.
We prove that an absolutely maximally entangled state of seven qudits exists if and only if the local dimension satisfies
d≥3. Prior to this work, to the best of our knowledge,
AME(7,d) states were known to exist only when
d is a prime power other than
2, or when
d can be expressed as a product of dimensions for which existence was already known. Since it has been proved that no
AME(7,2) state exists, it remains to establish existence for all
d≥3. We construct cyclic quadratic-phase states for every odd local dimension and develop a coupled binary--odd-dimensional construction for every dimension congruent to
2 modulo
4. Together with the known power-of-two cases and the product property of AME states, these constructions cover every local dimension
d≥3.
Absolutely maximally entangled (AME) states are pure multi-partite generalizations of the bipartite maximally entangled states with the property that all reduced states of at most half the system size are in the maximally mixed state. AME states are of interest for multipartite teleportation and quantum secret sharing and have recently found new applications in the context of high-energy physics in toy models realizing the AdS/CFT-correspondence. We work out in detail the connection between AME states of minimal support and classical maximum distance separable (MDS) error correcting codes and, in particular, provide explicit closed form expressions for AME states of
n parties with local dimension
q a power of a prime for all
q≥n−1. Building on this, we construct a generalization of the Bell-basis consisting of AME states and develop a stabilizer formalism for AME states. For every
q≥n−1 prime we show how to construct QECCs that encode a logical qudit into a subspace spanned by AME states. Under a conjecture for which we provide numerical evidence, this construction produces a family of quantum error correcting codes
[[n,1,n/2]]q for
n even, saturating the quantum Singleton bound. We show that our conjecture is equivalent to the existence of an operator whose support cannot be decreased by multiplying it with stabilizer products and explicitly construct the codes up to
n=8.
Absolutely maximally entangled, AME, states are pure multipartite states that give rise to the maximally mixed states when half or more of the parties are traced out. AME states find applications in fields like teleportation or quantum secret sharing, and the problem of finding conditions on their existence has been considered in a number of papers. We consider here AME states of minimal support, that are simpler to analyse. An equivalence with coding theory gives a sufficient condition for their existence, that the number of sites be equal to the local dimension plus one, when the local dimension
d is a power of a prime number. In this paper, an equivalence with latin hypercubes is used to prove that the above sufficient condition fails in the first case in which the local dimension is not a prime power,
d=6. Results for other values of
d are also given.
Absolutely maximally entangled (AME) states represent an extreme form of multipartite entanglement: every reduced system containing at most half of the parties is maximally mixed. These states provide perfect tensors and optimal quantum error-correcting codes, yet their existence is known only in restricted parameter regimes. For every odd prime power
q=pe≥3, we construct a stabilizer
AME(2q,q) state whose normalized one-party projection yields a stabilizer
AME(2q−1,q) state. A closed-form
q×q bordered-circulant matrix
Aq over
Fq2 generates a Hermitian self-dual maximum distance separable (MDS) code
[2q,q,q+1]q2, which lies outside the extended Reed-Solomon classes. In suitable bases, the amplitude tensors define normalized
q-unitary complex Hadamard matrices of order
qq with
pth-root phases. Additional constructions yield
AME(q+3,q) states and families at intermediate particle numbers through explicit rescalings of selected submatrices. We also provide nine explicit parent matrices and the corresponding one-party projections.
Absolutely maximally entangled (AME) states and, more generally,
k-uniform states in $(\C^q)^{\otimes n}$ are central objects in multipartite entanglement theory, with applications to quantum secret sharing, quantum masking, and quantum error correction. In the extremal case
k=⌊n/2⌋, Scott (2004) proved a sharp nonexistence bound showing that AME states cannot exist once the number of parties
n exceeds a threshold of order
2q2 (with a parity dependence on
n), where
q is the local dimension. Recently, Ning et al.\ studied \emph{defective} AME states (i.e.,
k=⌊n/2⌋−l with
l>0), gave explicit Scott-type bounds for defects
l=1,2 and conjectured a general
(2l+2)q2+o(q2) behavior. In this paper, we solve this conjecture and establish a fully explicit Scott-type upper bound for AME states with arbitrary defect
l≥0, yielding Scott's bound for
l=0 and Ning et al.'s bounds for
l=1,2 as special cases. Equivalently, this gives nonexistence bounds for one-dimensional pure quantum error-correcting codes near the quantum Singleton regime. The proof uses a truncated MacWilliams linear-programming system and an explicit infeasibility certificate. As a direct application, we derive explicit asymptotic upper bounds on
k/n for fixed local dimension
q, improving the implicit upper bounds given by Ning et al.