Explicit construction of a 2-design of ${\rm U}(2)$ from the theory of angular momentum

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Hauptverfasser: Maggi, Rocco, Lupo, Cosmo, Pascazio, Saverio
Format: Preprint
Veröffentlicht: 2025
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author Maggi, Rocco
Lupo, Cosmo
Pascazio, Saverio
author_facet Maggi, Rocco
Lupo, Cosmo
Pascazio, Saverio
contents The main aim of this work is to present an explicit construction of a 2-design of ${\rm U}(2)$, relying only on a tool that belongs to every physicists toolbox: the theory of angular momentum. Unitary designs are a rich and fundamental mathematical topic, with numerous fruitful applications in quantum information science and technology. In this work we take a peek under the hood. We begin with a minimal set of definitions and characterizations. Then we derive all 1-designs of ${\rm U}(2)$ of minimum size. Finally, we set out, step by step, a completion procedure extending such 1-designs to 2-designs. In particular, starting from the Pauli basis $\unicode{x2014}$ the prototypical unitary 1-design $\unicode{x2014}$ one $\unicode{x201C}$naturally$\unicode{x201D}$ obtains the 2-design originally employed by Bennett and coauthors in $\textit{Mixed State Entanglement and Quantum Error Correction}$. The present work also serves as a gentle and largely self-contained introduction to the subject.
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id arxiv_https___arxiv_org_abs_2509_17127
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Explicit construction of a 2-design of ${\rm U}(2)$ from the theory of angular momentum
Maggi, Rocco
Lupo, Cosmo
Pascazio, Saverio
Quantum Physics
Mathematical Physics
The main aim of this work is to present an explicit construction of a 2-design of ${\rm U}(2)$, relying only on a tool that belongs to every physicists toolbox: the theory of angular momentum. Unitary designs are a rich and fundamental mathematical topic, with numerous fruitful applications in quantum information science and technology. In this work we take a peek under the hood. We begin with a minimal set of definitions and characterizations. Then we derive all 1-designs of ${\rm U}(2)$ of minimum size. Finally, we set out, step by step, a completion procedure extending such 1-designs to 2-designs. In particular, starting from the Pauli basis $\unicode{x2014}$ the prototypical unitary 1-design $\unicode{x2014}$ one $\unicode{x201C}$naturally$\unicode{x201D}$ obtains the 2-design originally employed by Bennett and coauthors in $\textit{Mixed State Entanglement and Quantum Error Correction}$. The present work also serves as a gentle and largely self-contained introduction to the subject.
title Explicit construction of a 2-design of ${\rm U}(2)$ from the theory of angular momentum
topic Quantum Physics
Mathematical Physics
url https://arxiv.org/abs/2509.17127