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Whether parameterized quantum circuits (PQCs) can be systematically constructed to be both trainable and expressive remains an open question. Highly expressive PQCs often exhibit barren plateaus, while several trainable alternatives admit…

Quantum Physics · Physics 2026-03-17 Peter Röseler , Dennis Willsch , Kristel Michielsen

Ansatz selection is a key factor in the performance of variational quantum algorithms (VQAs). While much of the state-of-the-art still relies on heuristic choices, an inadequate circuit structure can compromise both the expressive power and…

Quantum Physics · Physics 2026-03-24 Rodrigo M. Sanz , Andreu Angles-Castillo , Eduard Alarcon , Carmen G Almudever

The hybrid quantum-classical algorithm is actively examined as a technique applicable even to intermediate-scale quantum computers. To execute this algorithm, the hardware efficient ansatz is often used, thanks to its implementability and…

Quantum Physics · Physics 2021-04-21 Kouhei Nakaji , Naoki Yamamoto

Parameterized quantum circuits used as variational ans\"atze are emerging as promising tools to tackle complex problems ranging from quantum chemistry to combinatorial optimization. These variational quantum circuits can suffer from the…

Quantum Physics · Physics 2023-12-14 Valentin Heyraud , Zejian Li , Kaelan Donatella , Alexandre Le Boité , Cristiano Ciuti

Quantifying the flatness of the objective-function landscape associated with unstructured parameterized quantum circuits is important for understanding the performance of variational algorithms utilizing a "hardware-efficient ansatz",…

Quantum Physics · Physics 2022-03-14 John Napp

The expressibility of an ansatz used in a variational quantum algorithm is defined as the uniformity with which it can explore the space of unitary matrices, i.e., its covering number. The expressibility of a particular ansatz has a…

Quantum Physics · Physics 2025-01-09 Tamojit Ghosh , Arijit Mandal , Shreya Banerjee , Neetik Mukherjee , Prasanta K. Panigrahi

Variational quantum algorithms have emerged as a leading paradigm that extracts practical computation from near-term intermediate-scale quantum devices, enabling advances in quantum chemistry simulations, combinatorial optimization, and…

Quantum Physics · Physics 2026-02-24 Manish Mallapur , Ronit Raj , Ankur Raina

Barren plateaus appear to be a major obstacle to using variational quantum algorithms to simulate large-scale quantum systems or replace traditional machine learning algorithms. They can be caused by multiple factors such as expressivity,…

Quantum Physics · Physics 2023-08-10 Cenk Tüysüz , Giuseppe Clemente , Arianna Crippa , Tobias Hartung , Stefan Kühn , Karl Jansen

In this paper, we propose a framework to study the combined effect of several factors that contribute to the barren plateau problem in quantum neural networks (QNNs), which is a critical challenge in quantum machine learning (QML). These…

Quantum Physics · Physics 2023-12-06 Muhammad Kashif , Saif Al-Kuwari

With the exponentially faster computation for certain problems, quantum computing has garnered significant attention in recent years. Variational quantum algorithms are crucial methods to implement quantum computing, and an appropriate…

Quantum Physics · Physics 2025-11-18 Fei Zhang , Jie Li , Zhimin He , Haozhen Situ

Sampling from a probability distribution is a core task in many quantum and classical algorithms. Variational quantum circuits provide a natural approach to generating such distributions, as measurement outcomes directly define the…

Quantum Physics · Physics 2026-01-06 Ronit Raj , Kshitij Durge , Manish Mallapur , Rohit Taeja Kumar , Ankur Raina

Variational Quantum Eigensolver is considered promising for medium-scale noisy quantum computers. Expressibility is an important metric for measuring the capability of a variational quantum Ansatz circuit. A commonly used method to increase…

Quantum Physics · Physics 2024-06-18 Peng Wang , Ruyu Yang

In the search for quantum advantage with near-term quantum devices, navigating the optimization landscape is significantly hampered by the barren plateaus phenomenon. This study presents a strategy to overcome this obstacle without changing…

Quantum Physics · Physics 2025-03-11 Yuhan Yao , Yoshihiko Hasegawa

Quantum supervised learning, utilizing variational circuits, stands out as a promising technology for NISQ devices due to its efficiency in hardware resource utilization during the creation of quantum feature maps and the implementation of…

Quantum Physics · Physics 2023-11-15 Anton Simen Albino , Rodrigo Bloot , Otto M. Pires , Erick G. S. Nascimento

In the context of Variational Quantum Algorithms (VQAs), selecting an appropriate ansatz is crucial for efficient problem-solving. Hamiltonian expressibility has been introduced as a metric to quantify a circuit's ability to uniformly…

Parametrized quantum circuits initialized with random initial parameter values are characterized by barren plateaus where the gradient becomes exponentially small in the number of qubits. In this technical note we theoretically motivate and…

Quantum Physics · Physics 2019-12-11 Edward Grant , Leonard Wossnig , Mateusz Ostaszewski , Marcello Benedetti

Although we are currently in the era of noisy intermediate scale quantum devices, several studies are being conducted with the aim of bringing machine learning to the quantum domain. Currently, quantum variational circuits are one of the…

Quantum Physics · Physics 2023-06-23 Lucas Friedrich , Jonas Maziero

Random quantum circuits have been utilized in the contexts of quantum supremacy demonstrations, variational quantum algorithms for chemistry and machine learning, and blackhole information. The ability of random circuits to approximate any…

Quantum Physics · Physics 2023-03-23 Minzhao Liu , Junyu Liu , Yuri Alexeev , Liang Jiang

Many experimental proposals for noisy intermediate scale quantum devices involve training a parameterized quantum circuit with a classical optimization loop. Such hybrid quantum-classical algorithms are popular for applications in quantum…

Quantum Physics · Physics 2019-02-04 Jarrod R. McClean , Sergio Boixo , Vadim N. Smelyanskiy , Ryan Babbush , Hartmut Neven

Barren Plateaus are a formidable challenge for hybrid quantum-classical algorithms that lead to flat plateaus in the loss function landscape making it difficult to take advantage of the expressive power of parameterized quantum circuits…

Quantum Physics · Physics 2024-06-21 Michelle Gelman
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