Fourier Fingerprints of Ansatzes in Quantum Machine Learning

Fuente: arXiv
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Main Authors: Strobl, Melvin, Sahin, M. Emre, van der Horst, Lucas, Kuehn, Eileen, Streit, Achim, Jaderberg, Ben
Format: Preprint
Published: 2025
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author Strobl, Melvin
Sahin, M. Emre
van der Horst, Lucas
Kuehn, Eileen
Streit, Achim
Jaderberg, Ben
author_facet Strobl, Melvin
Sahin, M. Emre
van der Horst, Lucas
Kuehn, Eileen
Streit, Achim
Jaderberg, Ben
contents Typical schemes to encode classical data in variational quantum machine learning (QML) lead to quantum Fourier models with $\mathcal{O}(\exp(n))$ Fourier basis functions in the number of qubits. Despite this, in order for the model to be efficiently trainable, the number of parameters must scale as $\mathcal{O}(\mathrm{poly}(n))$. This imbalance implies the existence of correlations between the Fourier modes, which depend on the structure of the circuit. In this work, we demonstrate that this phenomenon exists and show cases where these correlations can be used to predict ansatz performance. For several popular ansatzes, we numerically compute the Fourier coefficient correlations (FCCs) and construct the Fourier fingerprint, a visual representation of the correlation structure. We subsequently show how, for the problem of learning random Fourier series, the FCC correctly predicts relative performance of ansatzes whilst the widely-used expressibility metric does not. Finally, we demonstrate how our framework applies to the more challenging problem of jet reconstruction in high-energy physics. Overall, our results demonstrate how the Fourier fingerprint is a powerful new tool in the problem of optimal ansatz choice for QML.
format Preprint
id arxiv_https___arxiv_org_abs_2508_20868
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Fourier Fingerprints of Ansatzes in Quantum Machine Learning
Strobl, Melvin
Sahin, M. Emre
van der Horst, Lucas
Kuehn, Eileen
Streit, Achim
Jaderberg, Ben
Quantum Physics
Typical schemes to encode classical data in variational quantum machine learning (QML) lead to quantum Fourier models with $\mathcal{O}(\exp(n))$ Fourier basis functions in the number of qubits. Despite this, in order for the model to be efficiently trainable, the number of parameters must scale as $\mathcal{O}(\mathrm{poly}(n))$. This imbalance implies the existence of correlations between the Fourier modes, which depend on the structure of the circuit. In this work, we demonstrate that this phenomenon exists and show cases where these correlations can be used to predict ansatz performance. For several popular ansatzes, we numerically compute the Fourier coefficient correlations (FCCs) and construct the Fourier fingerprint, a visual representation of the correlation structure. We subsequently show how, for the problem of learning random Fourier series, the FCC correctly predicts relative performance of ansatzes whilst the widely-used expressibility metric does not. Finally, we demonstrate how our framework applies to the more challenging problem of jet reconstruction in high-energy physics. Overall, our results demonstrate how the Fourier fingerprint is a powerful new tool in the problem of optimal ansatz choice for QML.
title Fourier Fingerprints of Ansatzes in Quantum Machine Learning
topic Quantum Physics
url https://arxiv.org/abs/2508.20868