At a Glance
- Variational quantum algorithms, a promising computational method, frequently stall on “barren plateaus, ” preventing them from finding solutions to complex, large-scale scientific problems.
- This frustrating phenomenon is like being trapped on a featureless landscape, representing a significant roadblock that has challenged the quantum computing community for many years.
- Los Alamos National Laboratory scientists have published a comprehensive review synthesizing six years of global research into the causes and solutions for barren plateaus.
- The paper explains how these dead ends arise from issues like the “curse of dimensionality” and guides how algorithm design predicts and avoids them.
- Researchers conclude that the field must create novel, quantum-native methods instead of adapting classical techniques to finally unlock these powerful machines’ true potential.
Variational quantum algorithms, or VQAs, represent a promising hybrid computation approach, blending quantum mechanics’ power with classical optimization techniques. In this method, a quantum computer runs a program with adjustable settings or parameters, and a classical computer works to “train” those parameters, fine-tuning them to find the best solution to a complex problem. However, researchers often hit a frustrating wall called a “barren plateau.” This phenomenon stalls progress, preventing the algorithm from improving.
“Imagine a landscape of peaks and valleys,” said Marco Cerezo, the lead scientist on the Los Alamos National Laboratory team studying the issue in a Phys.org press release. “When optimizing a variational, or parameterized, quantum algorithm, one needs to tune a series of knobs that control the solution quality and move you in the landscape. Here, a peak represents a bad solution, and a valley represents a good solution. However, when researchers develop algorithms, they sometimes find their model has stalled and can neither climb nor descend. It’s stuck in this space we call a barren plateau.”
After six years of dedicated research into this critical issue, a Los Alamos-led team has published a comprehensive review article in Nature Reviews Physics. The paper synthesizes years of global research, providing the most complete overview of why barren plateaus occur, how to identify them, and how the field can move forward. It serves as a crucial guide for scientists working to unlock the potential of VQAs for real-world applications.
“Barren plateaus are not the only issue facing variational quantum computing, but it is the main issue at the moment,” said Martin Larocca, an author of the study and a researcher at the laboratory. “With this paper, we want to relay what we’ve learned about barren plateaus to the community and to show that we understand this phenomenon.”
The review article identifies the different origins of barren plateaus, including the “curse of dimensionality,” a common problem in data science where tasks become exponentially more difficult as the number of variables, or dimensions, increases. The team also discusses which algorithms will likely get stuck and which are designed to avoid the problem. Looking ahead, the researchers argue that the field must innovate beyond simply adapting classical computing methods for quantum systems.
“The story of barren plateaus reflects how we are thinking about optimization in quantum systems,” Cerezo said. “We can’t continue to copy and paste methods from classical computing into the quantum world.” Instead, the path forward requires developing new algorithms explicitly designed for the unique way quantum computers process information, a necessary step to transition these powerful machines from theoretical tools to practical problem-solvers.
References
- Larocca, M., Thanasilp, S., Wang, S., Sharma, K., Biamonte, J., Coles, P. J., Cincio, L., McClean, J. R., Holmes, Z., & Cerezo, M. (2025). Barren plateaus in variational quantum computing. Nature Reviews Physics, 7(4), 174–189. https://doi.org/10.1038/s42254-025-00813-9
- Los Alamos National Laboratory. (2025, June 12). Understanding quantum computing’s most troubling problem—The barren plateau. Phys.Org; Los Alamos National Laboratory. https://phys.org/news/2025-06-quantum-problem-barren-plateau.html
