Geometric quantum machine learning with horizontal quantum gates

In the current framework of geometric quantum machine learning, the canonical method for constructing a variational ansatz that respects the symmetry of some group action is by forcing the circuit to be equivariant, i.e., to commute with the action of the group. This can, however, be an overzealous...

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Main Authors: Roeland Wiersema, Alexander F. Kemper, Bojko N. Bakalov, Nathan Killoran
Format: Article
Language:English
Published: American Physical Society 2025-02-01
Series:Physical Review Research
Online Access:http://doi.org/10.1103/PhysRevResearch.7.013148
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author Roeland Wiersema
Alexander F. Kemper
Bojko N. Bakalov
Nathan Killoran
author_facet Roeland Wiersema
Alexander F. Kemper
Bojko N. Bakalov
Nathan Killoran
author_sort Roeland Wiersema
collection DOAJ
description In the current framework of geometric quantum machine learning, the canonical method for constructing a variational ansatz that respects the symmetry of some group action is by forcing the circuit to be equivariant, i.e., to commute with the action of the group. This can, however, be an overzealous constraint that greatly limits the expressivity of the circuit, especially in the case of continuous symmetries. We propose an alternative paradigm for the symmetry-informed construction of variational quantum circuits, based on homogeneous spaces, relaxing the overly stringent requirement of equivariance. We achieve this by introducing horizontal quantum gates, which only transform the state with respect to the directions orthogonal to those of the symmetry. We show that horizontal quantum gates are much more expressive than equivariant gates, and thus can solve problems that equivariant circuits cannot. For instance, a circuit comprised of horizontal gates can find the ground state of an SU(2)-symmetric model where the ground state spin sector is unknown—a task where equivariant circuits fall short. Moreover, for a particular subclass of horizontal gates based on symmetric spaces, we can obtain efficient circuit decompositions for our gates through the KAK theorem. Finally, we highlight a particular class of horizontal quantum gates that behave similarly to general SU(4) gates, while achieving a quadratic reduction in the number of parameters for a generic problem.
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spelling doaj-art-708c493bdfdc45ccb2fe852c82c70a1d2025-02-10T16:39:31ZengAmerican Physical SocietyPhysical Review Research2643-15642025-02-017101314810.1103/PhysRevResearch.7.013148Geometric quantum machine learning with horizontal quantum gatesRoeland WiersemaAlexander F. KemperBojko N. BakalovNathan KilloranIn the current framework of geometric quantum machine learning, the canonical method for constructing a variational ansatz that respects the symmetry of some group action is by forcing the circuit to be equivariant, i.e., to commute with the action of the group. This can, however, be an overzealous constraint that greatly limits the expressivity of the circuit, especially in the case of continuous symmetries. We propose an alternative paradigm for the symmetry-informed construction of variational quantum circuits, based on homogeneous spaces, relaxing the overly stringent requirement of equivariance. We achieve this by introducing horizontal quantum gates, which only transform the state with respect to the directions orthogonal to those of the symmetry. We show that horizontal quantum gates are much more expressive than equivariant gates, and thus can solve problems that equivariant circuits cannot. For instance, a circuit comprised of horizontal gates can find the ground state of an SU(2)-symmetric model where the ground state spin sector is unknown—a task where equivariant circuits fall short. Moreover, for a particular subclass of horizontal gates based on symmetric spaces, we can obtain efficient circuit decompositions for our gates through the KAK theorem. Finally, we highlight a particular class of horizontal quantum gates that behave similarly to general SU(4) gates, while achieving a quadratic reduction in the number of parameters for a generic problem.http://doi.org/10.1103/PhysRevResearch.7.013148
spellingShingle Roeland Wiersema
Alexander F. Kemper
Bojko N. Bakalov
Nathan Killoran
Geometric quantum machine learning with horizontal quantum gates
Physical Review Research
title Geometric quantum machine learning with horizontal quantum gates
title_full Geometric quantum machine learning with horizontal quantum gates
title_fullStr Geometric quantum machine learning with horizontal quantum gates
title_full_unstemmed Geometric quantum machine learning with horizontal quantum gates
title_short Geometric quantum machine learning with horizontal quantum gates
title_sort geometric quantum machine learning with horizontal quantum gates
url http://doi.org/10.1103/PhysRevResearch.7.013148
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