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Quantum machine learning -- and specifically Variational Quantum Algorithms (VQAs) -- offers a powerful, flexible paradigm for programming near-term quantum computers, with applications in chemistry, metrology, materials science, data…

Quantum Physics · Physics 2024-03-15 M. Bilkis , M. Cerezo , Guillaume Verdon , Patrick J. Coles , Lukasz Cincio

We propose an algorithm for variational quantum algorithms (VQAs) to optimize the structure of parameterized quantum circuits (PQCs) efficiently. The algorithm optimizes the PQC structure on-the-fly in VQA by sequentially replacing a…

Quantum Physics · Physics 2024-05-17 Kaito Wada , Rudy Raymond , Yuki Sato , Hiroshi C. Watanabe

We present a systematic study of how quantum circuit design, specifically the depth of the variational ansatz and the choice of quantum feature mapping, affects the performance of hybrid quantum-classical neural networks on a causal…

Quantum Physics · Physics 2026-02-10 Silvie Illésová , Tomasz Rybotycki , Piotr Gawron , Martin Beseda

Variational quantum algorithms, which combine highly expressive parameterized quantum circuits (PQCs) and optimization techniques in machine learning, are one of the most promising applications of a near-term quantum computer. Despite their…

Quantum Physics · Physics 2024-02-07 Chae-Yeun Park , Nathan Killoran

Variational Quantum Eigensolver (VQE) is a hybrid algorithm for finding the minimum eigenvalue/vector of a given Hamiltonian by optimizing a parametrized quantum circuit (PQC) using a classical computer. Sequential optimization methods,…

Quantum Physics · Physics 2024-05-17 Katsuhiro Endo , Yuki Sato , Rudy Raymond , Kaito Wada , Naoki Yamamoto , Hiroshi C. Watanabe

A significant hurdle in the noisy intermediate-scale quantum (NISQ) era is identifying functional quantum circuits. These circuits must also adhere to the constraints imposed by current quantum hardware limitations. Variational quantum…

Quantum Physics · Physics 2024-10-03 Akash Kundu

Variational quantum algorithms (VQAs) optimize the parameters $\vec{\theta}$ of a parametrized quantum circuit $V(\vec{\theta})$ to minimize a cost function $C$. While VQAs may enable practical applications of noisy quantum computers, they…

Quantum Physics · Physics 2021-03-23 M. Cerezo , Akira Sone , Tyler Volkoff , Lukasz Cincio , Patrick J. Coles

The adaptive derivative-assembled problem-tailored variational quantum eigensolver (ADAPT-VQE) is one of the most widely used algorithms for electronic structure calculations in quantum computers. It adaptively selects operators based on…

Chemical Physics · Physics 2025-08-29 Nonia Vaquero-Sabater , Abel Carreras , David Casanova

Quantum neural networks (QNNs) are widely employed as ans\"atze for solving variational problems, where their expressivity directly impacts performance. Yet, accurately characterizing QNN expressivity remains an open challenge, impeding the…

Quantum Physics · Physics 2026-05-28 Juan Yao

Variational hybrid quantum-classical algorithms are powerful tools to maximize the use of Noisy Intermediate Scale Quantum devices. While past studies have developed powerful and expressive ansatze, their near-term applications have been…

Quantum Physics · Physics 2021-06-30 Sukin Sim , Jonathan Romero , Jerome F. Gonthier , Alexander A. Kunitsa

Quantum computing holds the potential to revolutionize various fields by efficiently tackling complex problems. At its core are quantum circuits, sequences of quantum gates manipulating quantum states. The selection of the right quantum…

Software Engineering · Computer Science 2024-06-13 Xiaoyu Guo , Takahiro Muta , Jianjun Zhao

We introduce multiple parametrized circuit ans\"atze and present the results of a numerical study comparing their performance with a standard Quantum Alternating Operator Ansatz approach. The ans\"atze are inspired by mixing and phase…

Quantum Physics · Physics 2023-01-27 Ryan LaRose , Eleanor Rieffel , Davide Venturelli

A central component of variational quantum algorithms (VQA) is the state-preparation circuit, also known as ansatz or variational form. This circuit is most commonly designed to respect the symmetries of the problem Hamiltonian and, in this…

Recent quantum algorithms pertaining to electronic structure theory primarily focus on threshold-based dynamic construction of ansatz by selectively including important many-body operators. These methods can be made systematically more…

Quantum Physics · Physics 2024-08-26 Chayan Patra , Debaarjun Mukherjee , Sonaldeep Halder , Dibyendu Mondal , Rahul Maitra

Quantum Neural Networks (QNNs) offer a promising framework for integrating quantum computing principles into machine learning, yet their practical capabilities and limitations remain insufficiently studied. In this work, we systematically…

Quantum Physics · Physics 2026-03-31 Martyna Czuba , Patrick Holzer , Hein Zay Yar Oo

The energy extraction from quantum sources is a key task to develop new quantum devices such as quantum batteries (QB). In this context, one of the main figures of merit is the ergotropy, which measures the maximal amount of energy (as…

In recent years, Variational Quantum Algorithms (VQAs) have emerged as a promising approach for solving optimization problems on quantum computers in the NISQ era. However, one limitation of VQAs is their reliance on fixed-structure…

Quantum Physics · Physics 2026-03-03 Gloria Turati , Maurizio Ferrari Dacrema , Paolo Cremonesi

Quantum algorithms based on the variational principle have found applications in diverse areas with a huge flexibility. But as the circuit size increases the variational landscapes become flattened, causing the so-called Barren plateau…

Quantum Physics · Physics 2025-09-03 Fabio Tarocco , Davide Materia , Leonardo Ratini , Leonardo Guidoni

Variational quantum algorithms (VQAs) are expected to establish valuable applications on near-term quantum computers. However, recent works have pointed out that the performance of VQAs greatly relies on the expressibility of the ansatzes…

Quantum Physics · Physics 2022-08-15 Xia Liu , Geng Liu , Jiaxin Huang , Hao-Kai Zhang , Xin Wang

In this study, we apply 1D quantum convolution to address the task of time series forecasting. By encoding multiple points into the quantum circuit to predict subsequent data, each point becomes a feature, transforming the problem into a…