Paley I automorphism conjecture for finite-field SICs

From papers

Let q>11q>11 be a prime power with q3mod4q\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 Auts\operatorname{Aut}_s and Autw\operatorname{Aut}_w for the strong and weak automorphism groups used in the paper. Paley I automorphism conjecture. The group Auts(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 p3mod4p\equiv3\bmod4 dividing d8d-8, the associated SIC {xij}\{x_{ij}\} in Fp2d\mathbb F_{p^2}^d satisfies Auts({xij})=ι(Autw(H))\operatorname{Aut}_s(\{x_{ij}\})=\iota(\operatorname{Aut}_w(H)) and Autw({xij})=Auts(H~)\operatorname{Aut}_w(\{x_{ij}\})=\operatorname{Aut}_s(\tilde H). The paper proves that Auts(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.

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Sources & referencesView supporting material

Primary source

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

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