Parameter-optimal unitary synthesis with flag decompositions

Fuente: arXiv
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Autori principali: Kottmann, Korbinian, Wierichs, David, Alonso-Linaje, Guillermo, Killoran, Nathan
Natura: Preprint
Pubblicazione: 2026
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author Kottmann, Korbinian
Wierichs, David
Alonso-Linaje, Guillermo
Killoran, Nathan
author_facet Kottmann, Korbinian
Wierichs, David
Alonso-Linaje, Guillermo
Killoran, Nathan
contents We introduce the flag decomposition as a central tool for unitary synthesis. It lets us carve out a diagonal unitary with $2^n$ degrees of freedom in such a way that the remaining flag circuit is parametrized by the optimal number of $4^n-2^n$ rotations. This enables us to produce parameter-optimal quantum circuits for generic unitaries and matrix product state preparation. Our approach improves upon the state of the art, both when compiling down to the {Clifford + Rot} gate set with what we call selective de-multiplexing, and when using phase gradient resource states together with quantum arithmetic to implement multiplexed rotations. All of our synthesis methods are efficiently implementable in terms of recursive Cartan decompositions realized by standard linear algebra routines, making them applicable to all practically relevant system sizes.
format Preprint
id arxiv_https___arxiv_org_abs_2603_20376
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Parameter-optimal unitary synthesis with flag decompositions
Kottmann, Korbinian
Wierichs, David
Alonso-Linaje, Guillermo
Killoran, Nathan
Quantum Physics
We introduce the flag decomposition as a central tool for unitary synthesis. It lets us carve out a diagonal unitary with $2^n$ degrees of freedom in such a way that the remaining flag circuit is parametrized by the optimal number of $4^n-2^n$ rotations. This enables us to produce parameter-optimal quantum circuits for generic unitaries and matrix product state preparation. Our approach improves upon the state of the art, both when compiling down to the {Clifford + Rot} gate set with what we call selective de-multiplexing, and when using phase gradient resource states together with quantum arithmetic to implement multiplexed rotations. All of our synthesis methods are efficiently implementable in terms of recursive Cartan decompositions realized by standard linear algebra routines, making them applicable to all practically relevant system sizes.
title Parameter-optimal unitary synthesis with flag decompositions
topic Quantum Physics
url https://arxiv.org/abs/2603.20376