REVIEW 4 major objections 5 minor 3 cited by
The existence of non-classical orthogonal quantum Latin squares
T0 review · 4 major / 5 minor · reviewed 2026-08-15 · deepseek-v4-flash
Pith's one-line read Quantum Latin squares can be genuinely non-classical while also being idempotent, mutually orthogonal, or self-orthogonal, and the paper constructs such squares in almost every dimension using classical combinatorial designs.
desk verdict Existence theorems are likely right and are a real advance, but non-classicality is asserted rather than proved; the gap is real, easy to fix, and should not block peer review. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing machinery is a pair of transfer arguments from classical designs to quantum squares. The pairwise balanced design (PBD) construction treats a PBD($v,K$) as a blueprint: a PBD is a set of blocks in which every pair of elements occurs in exactly one block, and each block is regarded as a subspace spanned by its computational basis vectors. Blocks containing the distinguished element $0$ receive an idempotent QLS whose off-diagonal vectors lie in a non-computational basis of the block's remaining subspace, while all other blocks receive classical idempotent QLSs. Because any two blocks intersect in at most one element, vectors from different blocks are automatically orthogonal except at the shared index, which is what makes rows, columns, and orthogonality checks work. The filling-in-holes constructions start instead from classical holey Latin squares, such as 2-IMOLS($v;4$), 3-IMOLS($v;4$), ISOLS($v;4$), and idempotent conjugate-orthogonal incomplete Latin squares; each hole is then filled with a quantum Latin square on a non-computational basis of that hole subspace, and self-orthogonality is preserved in the same way. Small explicit arrays for $v=6,8,10,11$ handle the low orders, and classical existence theorems for PBDs, IMOLSs, and ISOLSs provide the remaining orders.
What would settle it
A direct test is to check whether all vectors appearing in one of the paper's explicit arrays lie in a single orthonormal basis; if they do, the square is classical. For the $v=6$ idempotent array in Theorem 3.3, the top-left entry $|0\rangle$ and the entry $|+\rangle=(|0\rangle+|3\rangle)/\sqrt{2}$ are distinct but not orthogonal, so they cannot both belong to one orthonormal basis; applying this same orthogonality check to every array produced by Constructions 2.2, 2.6, and 2.8 would settle whether the non-classicality premise holds in general.
Extended reading notes
Core claim
The central discovery is that classical combinatorial design existence can be lifted to quantum non-classical existence. Concretely, the paper claims: (1) for $v\geq 6$ there is a non-classical idempotent QLS($v$); (2) for $v\geq 6$ there is a non-classical 2-idempotent MOQLS($v$), except possibly for $v\in\{6,7,8,9,10,11,12,14,15,18,19,23\}$; (3) for $v\geq 4$ there is a non-classical 2-MOQLS($v$), except possibly for $v\in\{4,5,6,7\}$; (4) for $v\geq 16$ there is a non-classical 3-MOQLS($v$); and (5) for $v\geq 13$ there is a non-classical SOQLS($v$). The constructions are explicit: they take a pairwise balanced design or a holey/incomplete Latin square, index rows and columns by a computational basis, and fill some blocks or holes with quantum Latin squares whose vectors come from non-computational bases of the block subspaces. The paper's operative criterion for non-classicality is that mixing computational-basis entries with non-computational block-basis entries prevents the whole array from being equivalent to a classical square.
Load-bearing premise
The load-bearing premise is the unproved assertion that a square mixing computational-basis vectors with vectors from non-computational bases of block subspaces is automatically non-classical; if some single invertible change of basis could rotate all those vectors into one common orthonormal basis, the constructed squares would be classical and the existence theorems would collapse.
Editorial extensions
If this is right
- For every $v\geq 8$ there is a non-classical pair of mutually orthogonal quantum Latin squares, and for every $v\geq 16$ a non-classical triple; the only unresolved orthogonality orders are the short exception lists in the theorems.
- For every $v\geq 13$ there is a non-classical self-orthogonal quantum Latin square, so quantum self-orthogonality is available in essentially all large dimensions.
- Idempotency does not block non-classicality: non-classical idempotent QLSs start at $v=6$, and non-classical 2-idempotent MOQLSs cover all $v\geq 6$ outside a finite set.
- The constructions are explicit, so each existence theorem yields actual arrays that can be used as ingredients for unitary error bases, mutually unbiased bases, $k$-uniform states, and quantum error-correcting codes.
- Because the proofs use classical design existence as a black box, any future improvement in PBD, IMOLS, or ISOLS existence automatically shrinks the exception lists.
Reading between the lines
- The exception lists in Theorems 3.4 and 3.7 likely reflect the limits of the classical design inputs, not genuine non-existence; closing them by direct search or by specialized quantum designs would be the natural next test.
- The paper's non-classicality criterion suggests a sharper quantifier: the cardinality of a QLS, the number of distinct vectors up to phase, could be used to distinguish constructions, with PBD-built squares probably having larger cardinality than hole-filling ones.
- If the mixed-bases premise is false in some setting, the constructions would still produce classical squares, so a classification of when block-basis choices force non-classicality would be a useful follow-up.
- The same transfer idea could be applied to other classical structures, such as orthogonal arrays or nets, to produce non-classical quantum Latin squares with additional symmetry or higher mutual orthogonality.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper introduces idempotent, self-orthogonal, and holey quantum Latin squares and applies combinatorial design tools—pairwise balanced designs, incomplete Latin squares, and conjugate-orthogonal incomplete Latin squares—to construct non-classical mutually orthogonal QLSs. The main claimed results are: a non-classical idempotent QLS(v) for every v≥6 (Theorem 3.3); a non-classical 2-idempotent MOQLS(v) for v≥6 except possibly {6,...,12,14,15,18,19,23} (Theorem 3.4); a non-classical 2-MOQLS(v) for v≥4 except possibly {4,5,6,7} (Theorem 3.7); a non-classical 3-MOQLS(v) for v≥16 (Theorem 3.8); and a non-classical SOQLS(v) for v≥13 (Theorem 3.9). Theorem 3.2 and the appendix assert that no non-classical idempotent QLS exists for v=3,4,5.
Significance. If the proofs are completed, the paper would extend the known existence ranges for non-classical orthogonal quantum Latin squares and add structural properties (idempotence, self-orthogonality) that are new in this context. The PBD and filling-in-holes constructions are natural and potentially reusable, and the explicit exception sets are falsifiable predictions. The paper does not ship machine-checked proofs or code, and it does not fit any parameters; the central constructions are concrete. The significance is moderate: the area has active connections to unitary error bases, mutually unbiased bases, and k-uniform states, but the value of the paper depends on closing the proof gaps below.
major comments (4)
- [§2, Constructions 2.2, 2.3, 2.6, 2.8, 2.11; Theorems 3.3 and 3.7] The non-classicality of every constructed (and explicitly displayed) square is asserted rather than proved. For example, the last line of Construction 2.2 says the square is non-classical 'since the elements are from computational basis or non-computational basis', and Construction 2.6 says the same because the holes are filled with squares based on non-computational bases. No argument rules out a global unitary U that sends all the mixed block bases to one computational basis. This is load-bearing: every existence theorem in the paper is about non-classical squares, and if the assertion failed for any construction, the corresponding theorem would still produce QLSs but lose the advertised property. A short proof is available: in each construction the classical parts contain the full computational basis {|0>,...,|v−1>} as entries, while at least one entry is a superposition such as (|i>+|j>)/√2; a unitary that maps every computational-basis entry to a basis vector must permute the computational basis, and then the superposition is not sent to a basis vector. The manuscript should state and prove this lemma once and apply it explicitly to each construction and to the displayed squares in Theorems 3.3 and 3.7.
- [Construction 2.3, proof of Eq. (3)] The proof of mutual orthogonality for two different blocks B1≠B2 is not valid as written. The text claims that if ⟨Φfi(x1,y1)|Φfi(x2,y2)⟩≠0 and ⟨Φfj(x1,y1)|Φfj(x2,y2)⟩≠0, then the first overlap is witnessed by an element xm and the second by an element xn with xm≠xn, so span{|xm>,|xn>}⊆LB1∩LB2, contradicting |B1∩B2|≤1. But LB1∩LB2 is a fixed subspace; if it is one-dimensional, both non-zero overlaps can be caused by the same intersection element, and the claimed contradiction does not follow. A correct argument is needed, for example based on the fact that B0-off-diagonal entries are supported on span(B\{0}) while B'-off-diagonal entries avoid the intersection element. As written, the mutual orthogonality of the t squares is unproved, and Theorem 3.4 depends on it.
- [Appendix A (proof of Theorem 3.2(3))] The v=5 non-existence proof is a long handwritten case analysis with many branches represented by small diagrams. Several branches are dismissed with 'obviously this case is contradictory to the definition of the QLS', and Cases 2–4 are handled only by saying that they can be discussed 'in the way of Case 1' without presenting the details. Since Theorem 3.2(3) is used to assert that no non-classical 2-idempotent MOQLS(5) exists (Theorem 3.4), the appendix needs to be either completed with all subcases or replaced by a machine-verified exhaustive enumeration. If a missing subcase contains a non-classical idempotent QLS(5), the claimed exception set changes.
- [Construction 2.5] Construction 2.5 is stated as: if there exists an HLS(v;v1,...,vn) and an LS(vs) for 1≤s≤n, then there exists a non-classical QLS(v). Taken literally, filling the holes with Latin squares on the computational basis produces a classical QLS, not a non-classical one. The intended statement must be that the hole squares are quantized with non-computational bases, and the non-classicality then needs the same global-unitary proof as in the first major comment. Because Theorem 3.6 and part of Theorem 3.3 invoke Construction 2.5, this imprecision is load-bearing and should be corrected.
minor comments (5)
- [Theorem 3.4] The notation '{6−12,14,15,18,19,23}' should be written unambiguously as '{6,7,8,9,10,11,12,14,15,18,19,23}' or with an en-dash; the minus sign is confusing.
- [Lemma 3.1] The displayed array in the proof of Lemma 3.1 is garbled; please redraw it so that the positions of |x⟩, |m⟩, |y⟩, |z⟩, |u⟩, and |v⟩ are clear.
- [Theorem 3.8] The citation to Lemma 1.1(4) is appropriate here, since that part gives N(4)≥3; no correction is needed for this citation.
- [Theorem 3.4, first paragraph] The proof states that a 2-idempotent MOQLS based on the computational basis exists for k∈{4,5,7,9,10,11}, but for blocks in B0 of Construction 2.3 one must relabel the non-zero part of each block to a non-computational basis. This is a harmless relabeling, but it should be stated explicitly so that the hypothesis of Construction 2.3 is visibly satisfied.
- [Construction 2.6, Cases 2 and 5] The phrase 'with contradiction' in Cases 2 and 5 is too terse. The contradiction is that the original holey squares have no outside cell whose tensor product lies in Vs⊗Vs; spelling this out would improve the readability.
Circularity Check
No significant circularity: the main existence theorems are derived from standard external design-theoretic lemmas and explicit constructions, with no fitted parameter renamed as a prediction.
full rationale
The paper's central claims -- non-classical 2-idempotent MOQLS(v), 2-MOQLS(v), 3-MOQLS(v), and SOQLS(v) for large v -- are obtained by combining classical existence results (MOLS, PBDs, IMOLSs, COILSs, ISOLSs) with new PBD and filling-in-holes constructions. No quantity is fitted to data and no conclusion is assumed in its own proof. The only self-citations are to prior published work by co-authors ([26], and within the pooled Lemma 1.2), used for subsidiary facts such as the existence of a non-classical 2-MOQLS(9) and the basic hole-filling Construction 2.5; these are stated as external theorems with their own proofs and do not presuppose the present existence theorems. The repeated assertion that a square is non-classical 'since the elements are from computational basis or non-computational basis' is a proof gap rather than circularity: having entries from two different bases is not definitionally equivalent to non-classicality, so the conclusion does not reduce to its premise. Similarly, the orthogonality argument in Construction 2.3 contains an unjustified implication about nonzero overlaps forcing a two-dimensional intersection, but this is a correctness issue, not a circular dependence. Overall the derivation chain is self-contained against standard benchmarks and no load-bearing step reduces to its own input.
Assumptions & free parameters
assumptions (6)
- domain assumption PBD existence: PBD(v,{3,4,5}) exists for v∉{6,8}; PBD(v,{4,5,7,9,10,11}) exists for v not in a listed finite set (Lemma 2.1).
- domain assumption Incomplete MOLS existence: 2-IMOLS(v;4) for v≥12, 3-IMOLS(v;4) for v≥16, ISOLS(v;4) for v≥13 (Lemma 2.4).
- domain assumption Idempotent (3,2,1)-COILS(v;n) exists for the parameters used, in particular n=4,5 for v=26,27,30 (Lemma 2.10).
- domain assumption Classical idempotent MOLS: N(1v)≥2 for v∉{2,3,6}; N(4)=3; SOLS(4) exists (Lemma 1.1).
- domain assumption Non-classical QLS(2) and QLS(3) do not exist (Lemma 3.5, cited to [18]).
- standard math Standard linear algebra facts about orthonormal bases, direct sums, and tensor products.
Cite this review
Pith. "Pith review of The existence of non-classical orthogonal quantum Latin squares." pith.science (2026). https://pith.science/paper/ZLV5KDVY
@misc{pith2026250720154,
author = {Pith},
title = {Pith review of: The existence of non-classical orthogonal quantum Latin squares},
year = {2026},
howpublished = {\url{https://pith.science/paper/ZLV5KDVY}},
note = {Machine review of arXiv:2507.20154}
}
abstract
Quantum Latin squares are a generalization of classical Latin squares in quantum field and have wide applications in unitary error bases, mutually unbiased bases, $k$-uniform states and quantum error correcting codes. In this paper, we put forward some new quantum Latin squares with special properties, such as idempotent quantum Latin square, self-orthogonal quantum Latin square, holey quantum Latin square, and the notions of orthogonality on them. We present some forceful construction methods including PBD constructions and filling in holes constructions for non-classical quantum Latin squares. As consequences, we establish the existence of non-classical 2-idempotent MOQLS$(v)$, non-classical 2, 3-MOQLS$(v)$ and non-classical SOQLS$(v)$ except possibly for several definite values.
Forward citations
Cited by 3 Pith papers
-
Large sets of mutually orthogonal quantum Latin squares
A set of n−2 mutually orthogonal quantum Latin squares of order n must be classical, and for prime powers q the paper constructs d−1 of them, one non-classical, whenever d>1 divides q−1.
-
Absolutely maximally entangled pure states of multipartite quantum systems
An updated survey of methods to generate absolutely maximally entangled states, with new analyses of reduced-state entanglement, GHZ superpositions, orthogonal frequency square representations, and local unitary equiv...
-
Controllable and Stealthy Shilling Attacks via Dispersive Latent Diffusion
The abstract promises a latent-diffusion shilling attack (DLDA) that promotes items and evades detection, but the full text is a different arXiv paper on quantum Latin squares, so the claimed result is completely unsupported.
Reference graph
Works this paper leans on
-
[1]
F. E. Bennett, B. Du, H. Zhang, Existence of self-orthogonal diagonal Latin squares with a missing subsquare. Discrete Math., 261 (2003) 69-86
work page 2003
-
[2]
F. E. Bennett, L. Zhu, Incomplete conjugate orthogonal idempotent latin squares. Elsevier Science Publishers B.V. (North-Holland), 65 (1987) 5-21. 12
work page 1987
-
[3]
R. C. Bose, A note on orthogonal arrays, Ann. Math. Stat. , 21 (1950) 304-305
work page 1950
-
[4]
S. Boyadzhiyska, S. Das, T. Szab´o, Enumerating extensions of mutually orthogonal Latin squares. Des. Codes Cryptogr., 88 (2020) 2187-2206
work page 2020
-
[5]
K. A. Bush, Orthogonal arrays of index unity, Ann. Math. Stat. , 23 (1952) 426-434
work page 1952
- [6]
-
[7]
C. J. Colbourn, J. H. Dinitz, The CRC Handbook of Combinatorial Designs. Chapman and Hall/CRC Press, 2007
work page 2007
- [8]
Show all 31 references
-
[9]
K. A. Donald, J. D´enes, Latin Squares and Their Applications. Elsevier, 2015
2015
-
[10]
Gao, Latin squares in experimental design
L. Gao, Latin squares in experimental design. Michigan State University , 2005
2005
-
[11]
Goyeneche, Z
D. Goyeneche, Z. Raissi, S. Di. Martino, et al., Entanglement and quantum combinatorial designs. Phys. Rev. A , 97 (2018) 062326
2018
-
[12]
Hayashi, M
A. Hayashi, M. Horibe, T. Hashimoto, Mean king’s problem with mutually unbiased bases and orthogonal Latin squares. Phys. Rev. A , 71 (2005) 052331
2005
-
[13]
A. S. Hedayat, N. J. A. Sloane, J. Stufken, Orthogonal Array: Theory and Applications, Springer-Verlag, 1999
1999
-
[14]
Heinrich, L
K. Heinrich, L. Zhu, Incomplete self-orthogonal latin squares. J. Austral. Math. Soc. , 42 (1987) 365-384
1987
-
[15]
C. F. Laywine, G. L. Mullen, Discrete mathematics using Latin squares. John Wiley and Sons, 1998
1998
-
[16]
Musto, Constructing mutually unbiased bases from quantum Latin squares
B. Musto, Constructing mutually unbiased bases from quantum Latin squares. EPTCS, 236 (2017) 108
2017
-
[17]
Musto, J
B. Musto, J. Vicary, Quantum Latin squares and unitary error bases. Quantum Inf. Com- put., 16 (2016) 1318
2016
-
[18]
Paczos, M Wierzbi´nski, G Rajchel-Mieldzio´c, et al., Genuinely quantum solutions of the game Sudoku and their cardinality
J. Paczos, M Wierzbi´nski, G Rajchel-Mieldzio´c, et al., Genuinely quantum solutions of the game Sudoku and their cardinality. Phys. Rev. A , 104 (2021) 042423
2021
-
[19]
S. K. Pal, S. Kapoor, A. Arora, et al., Design of strong cryptographic schemes based on Latin squares. J. Discrete Math. Sci. Cryptogr. , 13 (2010) 233-256
2010
-
[20]
Preskill, Quantum Computing in the NISQ era and beyond, Quantum, 2 (2018) 79
J. Preskill, Quantum Computing in the NISQ era and beyond, Quantum, 2 (2018) 79
2018
-
[21]
S. A. Rather, A. Burchardt, W. Bruzda, et al., Thirty-six entangled officers of Euler: Quan- tum solution to a classically impossible problem. Phys. Rev. Lett., 128 (2022) 080507
2022
-
[22]
D. J. Reutter, J. Vicary, Biunitary constructions in quantum information, Higher Structures, 3 (2019) 109-154
2019
-
[23]
V. A. Ryazanov, G. K. Duskaev, E. V. Sheida, et al., Effect of Artemisia absinthium (Aster- aceae) and cobalt supplementation on rumen bacterial community in cattle. Indian J Anim Res, 58 (2024) 1266-1274
2024
-
[24]
S. L. Squares, Sets of mutually orthogonal. College Math. J. , 408 (2009) 174-180. 13
2009
-
[25]
D. T. Todorov, Four mutually orthogonal Latin squares of order 14. J. Combin. Des. , 20 (2012) 363-367
2012
-
[26]
Y. Zang, P. Facchi, Z. Tian, Quantum combinatorial designs and k-uniform states. J. Phys. A: Math. Theor. , 54 (2021) 505204
2021
-
[27]
Zhu, Orthogonal latin squares with subsquares
L. Zhu, Orthogonal latin squares with subsquares. Discrete Math., 48 (1984) 315-321. Appendix: The continuation of the proof in Theorem 3.2. Proof (3)v = 5, we prove it in terms of cardinalityc of a QLS, the number of its vectors distinct up to a global phase. Suppose there ex...
1984
-
[28]
Because|Φ13⟩ =a0|0⟩+a1|2⟩→|Φ13⟩ = |2⟩,|Φ43⟩ = a0|1⟩ +a1|2⟩→|Φ43⟩ =|2⟩, which is a contradiction
Case 1-2-1 Suppose|Φ23⟩,|Φ24⟩ are the entangled states of|0⟩,|1⟩. Because|Φ13⟩ =a0|0⟩+a1|2⟩→|Φ13⟩ = |2⟩,|Φ43⟩ = a0|1⟩ +a1|2⟩→|Φ43⟩ =|2⟩, which is a contradiction. Hence |Φ23⟩ =|0⟩ or|1⟩. Furthermore, there are two cases: |0⟩ |2⟩ |1⟩ |4⟩ |3⟩ |1⟩ |4⟩ |3⟩ |2⟩ |0⟩ |1⟩ |4⟩ |3⟩ |0⟩ ...
-
[29]
This forms a classical idempotent QLS(5)
Case 1-2-2 Since the elements in each row and column of Φ form a standard orthogonal basis of C5, then |Φ32⟩ =|0⟩→| Φ42⟩ =|3⟩→| Φ12⟩ =|4⟩→| Φ23⟩ =|1⟩→| Φ20⟩ =|4⟩→| Φ43⟩ =|2⟩→| Φ40⟩ = |1⟩→| Φ30⟩ =|2⟩→| Φ10⟩ =|3⟩→| Φ13⟩ =|0⟩→| Φ14⟩ =|2⟩→| Φ34⟩ =|1⟩. This forms a classical idempo...
-
[30]
Case 1-3-1 Obviously, this case is contradictory to the definition of QLS, so it does not constitute an idempotent QLS(5)
-
[31]
Select |Φ11⟩,|Φ31⟩,|Φ33⟩, then we can determine |Φ30⟩ or|Φ32⟩ according to Lemma 3.1
Case 1-3-2 If|Φ20⟩,|Φ23⟩ are the entangled states of |1⟩,|4⟩, then |Φ23⟩ = |1⟩, |Φ20⟩ = |4⟩ because |Φ03⟩ = |4⟩,⟨Φ03|Φ23⟩ = 0. Select |Φ11⟩,|Φ31⟩,|Φ33⟩, then we can determine |Φ30⟩ or|Φ32⟩ according to Lemma 3.1. There will exist two cases. Similar to Case 1-2, there only exis...
Reviewed August 15, 2026 · model on record in the stance chip above.
Discussion (0). Continue with ORCID to comment.