Towards a classification of $6\times 6$ complex Hadamard matrices
Abstract
Complex Hadamard matrices have received considerable attention in the past few years due to their appearance in quantum information theory. While a complete characterization is currently available only up to order 5 (in \cite{haagerup}), several new constructions of higher order matrices have appeared recently \cite{dita, karol, BN, MM, sz}. In particular, the classification of {\it self-adjoint} complex Hadamard matrices of order 6 was completed by Beuachamp and Nicoara in \cite{BN}, providing a previously unknown non-affine one-parameter orbit. In this paper we classify all \emph{dephased, symmetric} complex Hadamard matrices \emph{with real diagonal} of order 6. Furthermore, relaxing the condition on the diagonal entries we obtain a new non-affine one-parameter orbit connecting the Fourier matrix and Di\c{t}\u{a}'s matrix . This answers a recent question of Bengtsson & al. in \cite{BB}.
Cite
@article{arxiv.math/0702043,
title = {Towards a classification of $6\times 6$ complex Hadamard matrices},
author = {Máté Matolcsi and Ferenc Szöllősi},
journal= {arXiv preprint arXiv:math/0702043},
year = {2007}
}
Comments
14 pages