← Open problems
MUB-10.4
Classify all complex Hadamard matrices of order six.
In plain terms
Conjecture 7.1: the known list (isolated S6, three-parameter K6(3), four-parameter G6(4)) is expected to be exhaustive, but no proof exists.
Our position — ours alone, not the authors'
A classification theorem over continuous families. Our instrument decides points, not families. No amount of compute closes this.
Source
Daniel McNulty, Stefan Weigert, Mutually Unbiased Bases in Composite Dimensions -- A Review
Quantum 10, 2051 (2026) · §10.2
https://doi.org/10.22331/q-2026-04-01-2051
Licence:
CC-BY-4.0
— the problem statement is quoted here under that
licence, with attribution, and has not been modified