Researchers Scale Quantum Circuit Simulation Beyond 40 Qubits

Insider Brief

Researchers from Osaka University’s QIQB and Fixstars achieved one of the largest classical simulations of quantum chemistry circuits using 1,024 GPUs, surpassing the previous 40-qubit limit.
The team implemented iterative quantum phase estimation (IQPE) in a GPU-based simulator and developed parallel computing methods to scale performance across large clusters.
The work expands the range of molecular systems for testing quantum algorithms, supporting future fault-tolerant quantum computing applications in chemistry and materials science.

PRESS RELEASE — A joint research team between the Center for Quantum Information and Quantum Biology (QIQB) at The University of Osaka and Fixstars Corporation has demonstrated one of the world’s largest classical simulations of iterative quantum phase estimation (IQPE) circuits for quantum chemistry on up to 1,024 GPUs, surpassing the previous 40-qubit limit. The result expands the scale of molecular systems available for the development and validation of quantum algorithms for future fault-tolerant quantum computers, supporting progress toward industrial applications in drug discovery and materials development.

Overcoming unresolved challenges in drug discovery and developing new materials to address climate change will require advanced quantum chemical calculations beyond the reach of current technology. Against this backdrop, fault-tolerant quantum computers (FTQC) are widely anticipated as a key enabling technology, making it increasingly important to develop and validate, ahead of their deployment, the quantum algorithms that will eventually run on such systems.

Quantum phase estimation (QPE) serves as a core subroutine in many quantum algorithms and, in quantum chemistry, is expected to enable analyses that are difficult for current classical computers. The research group, consisting of Professor Wataru Mizukami, Assistant Technical Staff Shoma Hiraoka, and Assistant Technical Staff Sho Nishida at QIQB, and Yusuke Teranishi of Fixstars Corporation, focused on Iterative QPE (IQPE), a QPE-based method that requires fewer qubits, and implemented it in the quantum circuit simulator for quantum chemistry, “chemqulacs-gpu.”

The group also developed and applied a new parallel computing technology to maximize the performance of large-scale GPU clusters. As a result, they exceeded the previous limit of 40 qubits for state-vector-based quantum circuit simulations for quantum chemistry reported in earlier studies and successfully carried out one of the world’s largest such simulations. The simulations achieved the following results:

Largest problem size: calculation of a 42-spin-orbital system for an H₂O molecule (with qubit reduction technology applied)
Largest circuit size: calculation of a 41-qubit circuit for an Fe₂S₂ molecule (pure circuit-scale benchmark)

To achieve this result, the team implemented IQPE in the quantum chemistry simulator “chemqulacs-gpu” and developed a parallel computing method optimized for large-scale GPU clusters. Using up to 1,024 NVIDIA H100 GPUs on AIST’s ABCI-Q system, the researchers overcame conventional computational bottlenecks and extended quantum circuit simulations of quantum algorithms for quantum chemistry beyond the previous 40-qubit limit.

This achievement expands the range of molecules that can be targeted in the development and validation of quantum algorithms and supports further progress toward more complex and realistic molecular simulations on future fault-tolerant quantum computers.

Comment from Professor Wataru Mizukami

“Large-scale simulation of quantum circuits using 1,024 GPUs in unison is technically demanding, and within the limited 48-hour computation window we repeatedly encountered unexpected issues. I am delighted that the team, led by two young researchers, Yusuke Teranishi and Shoma Hiraoka, persevered throughout the effort, and that, with prompt support from the ABCI-Q operations staff, we were able to achieve one of the world’s largest results. I hope this accomplishment will help accelerate the development of quantum algorithms.”

Research collaboration

This research was conducted as a collaborative study based on the research plan of Professor Mizukami at QIQB. QIQB led the research and development of methods for classically simulating IQPE quantum circuits on GPU clusters, and implemented the interface connecting the quantum chemistry layer to the simulation layer. Fixstars Corporation provided GPU performance profiling and optimization technologies, and was responsible for optimizing the simulation code and tuning its performance on ABCI-Q. This work resolved complex inter-GPU communication bottlenecks and enabled highly efficient circuit simulation

Summary

A joint research team between the Center for Quantum Information and Quantum Biology (QIQB) at The University of Osaka and Fixstars Corporation has demonstrated one of the world’s largest classical simulations of iterative quantum phase estimation (IQPE) quantum circuits for quantum chemistry on up to 1,024 GPUs, surpassing the previous 40-qubit limit. The result expands the scale of molecular systems available for the development and validation of quantum algorithms for future fault-tolerant quantum computers, supporting progress toward industrial applications in drug discovery and materials development.