A Review of Barren Plateaus in Variational Quantum Computing

A Review of Barren Plateaus in Variational Quantum Computing

1 May 2024 | Martín Larocca, Supanut Thanasilp, Samson Wang, Kunal Sharma, Jacob Biamonte, Patrick J. Coles, Lukasz Cincio, Jarrod R. McClean, Zoë Holmes, and M. Cerezo
This review provides a comprehensive overview of the Barren Plateau (BP) phenomenon in variational quantum computing. Variational quantum computing combines quantum and classical computing to solve problems, but BPs pose a significant challenge. BPs occur when the loss function or its gradients become exponentially flat with increasing system size, making optimization difficult. The phenomenon is attributed to the curse of dimensionality, where the exponentially large Hilbert space dimension can lead to issues if not properly managed. The review discusses different types of BPs, including probabilistic and deterministic BPs, and their implications for training variational quantum algorithms. It also explores the origins of BPs, such as the expressive power of parametrized quantum circuits (PQCs), input states, and measurement operators. The study of BPs has influenced other fields like quantum optimal control, tensor networks, and learning theory. The review highlights strategies to avoid or mitigate BPs, such as using shallow circuits, alternative initializations, and modifying the loss function. It also discusses the impact of hardware noise on BPs and the connection between BPs and classical simulability. The review concludes with an outlook on future research directions, emphasizing the importance of understanding BPs for the development of efficient variational quantum algorithms.This review provides a comprehensive overview of the Barren Plateau (BP) phenomenon in variational quantum computing. Variational quantum computing combines quantum and classical computing to solve problems, but BPs pose a significant challenge. BPs occur when the loss function or its gradients become exponentially flat with increasing system size, making optimization difficult. The phenomenon is attributed to the curse of dimensionality, where the exponentially large Hilbert space dimension can lead to issues if not properly managed. The review discusses different types of BPs, including probabilistic and deterministic BPs, and their implications for training variational quantum algorithms. It also explores the origins of BPs, such as the expressive power of parametrized quantum circuits (PQCs), input states, and measurement operators. The study of BPs has influenced other fields like quantum optimal control, tensor networks, and learning theory. The review highlights strategies to avoid or mitigate BPs, such as using shallow circuits, alternative initializations, and modifying the loss function. It also discusses the impact of hardware noise on BPs and the connection between BPs and classical simulability. The review concludes with an outlook on future research directions, emphasizing the importance of understanding BPs for the development of efficient variational quantum algorithms.
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