Strong modular Zauner's conjecture for Hilbert C*-modules

Let A\mathcal{A} be a unital C*-algebra with the invariant basis number property or let A\mathcal{A} be a W*-algebra. For dNd\in\mathbb{N}, consider unit inner product frames in the standard module Ad\mathcal{A}^d, with 1d+1\frac{1}{d+1}-equiangularity meaning that mutual inner-product products equal 1d+1\frac{1}{d+1}. Strong modular Zauner's conjecture. For every dNd\in\mathbb{N}, there exists a 1d+1\frac{1}{d+1}-equiangular unit inner product frame {τj}j=1d2\{\tau_j\}_{j=1}^{d^2} for Ad\mathcal{A}^d, equivalently a tight frame with unit diagonal inner products and

τj,τkτk,τj=1d+1,1j,kd2, jk.\langle\tau_j,\tau_k\rangle\langle\tau_k,\tau_j\rangle=\frac{1}{d+1},\qquad 1\leq j,k\leq d^2,\ j\neq k.

The extra algebraic hypotheses define the strong form of the modular extension of Zauner's conjecture. The supplied text does not state whether this form is open, solved, or refuted.

Sources & referencesView supporting material

Primary source

K. Mahesh Krishna, “Modular Welch Bounds with Applications”, arXiv:2201.00319 (2022).

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