Paley I automorphism conjecture for finite-field SICs

Let q>11q>11 be a prime power with q≡3 mod 4q\equiv3\bmod4, let d=q+1d=q+1, and let HH be the Paley I Hadamard matrix of order dd. Write H~\tilde H for the associated object and Aut⁡s\operatorname{Aut}_s and Aut⁡w\operatorname{Aut}_w for the strong and weak automorphism groups used in the paper. Paley I automorphism conjecture. The group Aut⁡s(H~)≅PΓL(2,q)\operatorname{Aut}_s(\tilde H)\cong P\Gamma L(2,q) has exactly two orbits on [d]×[d][d]\times[d], namely {(i,i):i∈[d]}\{(i,i):i\in[d]\} and its complement; moreover, for every prime p≡3 mod 4p\equiv3\bmod4 dividing d−8d-8, the associated SIC {xij}\{x_{ij}\} in Fp2d\mathbb F_{p^2}^d satisfies Aut⁡s({xij})=ι(Aut⁡w(H))\operatorname{Aut}_s(\{x_{ij}\})=\iota(\operatorname{Aut}_w(H)) and Aut⁡w({xij})=Aut⁡s(H~)\operatorname{Aut}_w(\{x_{ij}\})=\operatorname{Aut}_s(\tilde H). The paper proves that Aut⁡s(H~)\operatorname{Aut}_s(\tilde H) contains a copy of PΓL(2,q)P\Gamma L(2,q) with the stated orbits, but does not prove the reverse inclusion; consequently the conjecture remains open.

References

Primary source

Joseph W. Iverson and Dustin G. Mixon, “Asymmetric SICs over finite fields”, arXiv:2506.20778 (2025).

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