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Clifford groups are not always 2-designs

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arxiv 2108.04200 v1 pith:CWDSCH2D submitted 2021-08-09 quant-ph

Clifford groups are not always 2-designs

classification quant-ph
keywords groupunitaryclifforddesigndesignsprimeproveaction
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The Clifford group is the quotient of the normalizer of the Weyl-Heisenberg group in dimension $d$ by its centre. We prove that when $d$ is not prime the Clifford group is not a group unitary $2$-design. Furthermore, we prove that the multipartite Clifford group is not a group unitary 2-design except for the known cases wherein the local Hilbert space dimensions are a constant prime number. We also clarify the structure of projective group unitary $2$-designs. We show that the adjoint action induced by a group unitary $2$-design decomposes into exactly two irreducible components; moreover, a group is a unitary 2-design if and only if the character of its so-called $U\overline{U}$ representation is $\sqrt{2}$.

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Cited by 2 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Quantum Universality in Composite Systems: A Trichotomy of Clifford Resources

    quant-ph 2025-12 unverdicted novelty 8.0

    Single-qudit universality for Clifford gate sets plus one non-Clifford gate follows a trichotomy determined by the prime factorization of the local dimension d.

  2. Simple slow operators and quantum thermalization

    quant-ph 2026-04 conditional novelty 6.0

    Absence of simple slow operators implies that typical low-complexity states thermalize in quantum systems.