More mutually unbiased bases
Abstract
Mutually unbiased bases (MUBs) describe quantum measurements for which certainty in one basis gives uniform outcomes in the others. Their maximum number remains unknown in dimensions that are not powers of a prime. We introduce an ansatz that, in many dimensions, allows us to construct more MUBs than have previously been found. Each basis in the ansatz consists of a diagonal phase matrix applied to a fixed unitary, which is a tensor product of Fourier matrices and, optionally, any real Hadamard matrix. This construction yields five MUBs in dimension 12, six in dimensions 48, 96, and 192, seven in dimensions 36 and 108, and ten in dimension 648. These bases can then be extended to exceed the tensor product bound, asymptotically, in every eighteenth dimension. Moreover, we show that Paley's real Hadamard matrix can be used to construct q+1 bases in dimension d = q(q+1) for every prime power q≡3pmod4. This count grows as √d and cannot be exceeded by tensor products of smaller sets.
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BibTeX
@misc{wuttig2026more,
title = {{More mutually unbiased bases}},
author = {Mateo Cárdenes Wuttig and Joseph Tindall},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.40311},
eprint = {2609.40311},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.40311},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - More mutually unbiased bases
AU - Mateo Cárdenes Wuttig
AU - Joseph Tindall
PY - 2026
DA - 2026/09/30
PB - arXiv
DO - 10.48550/arxiv.2609.40311
UR - https://arxiv.org/abs/2609.40311
AB - Mutually unbiased bases (MUBs) describe quantum measurements for which certainty in one basis gives uniform outcomes in the others. Their maximum number remains unknown in dimensions that are not powers of a prime. We introduce an ansatz that, in many dimensions, allows us to construct more MUBs than have previously been found. Each basis in the ansatz consists of a diagonal phase matrix applied to a fixed unitary, which is a tensor product of Fourier matrices and, optionally, any real Hadamard matrix. This construction yields five MUBs in dimension 12, six in dimensions 48, 96, and 192, seven in dimensions 36 and 108, and ten in dimension 648. These bases can then be extended to exceed the tensor product bound, asymptotically, in every eighteenth dimension. Moreover, we show that Paley's real Hadamard matrix can be used to construct q+1 bases in dimension d = q(q+1) for every prime power q≡3pmod4. This count grows as √d and cannot be exceeded by tensor products of smaller sets.
ER -