PNNL researchers are advancing the next generation of quantum algorithms and materials

April 14, 2022 — Quantum computers are expected to revolutionize the way researchers solve difficult computational problems. These computers are designed to meet major challenges in areas of basic research, such as quantum chemistry. In its current stage of development, quantum computing is still very sensitive to noise and environmental disturbances. This makes quantum computing “noisy” because quantum bits – or qubits – lose information as they go out of sync, a process called decoherence.

To overcome the limitations of current quantum computers, researchers from Pacific Northwest National Laboratory (PNNL) develop simulations that provide insight into how quantum computers work.

Quantum circuit simulation can reveal the impact of noise on intermediate-scale quantum devices. (Composite image by Donald Jorgensen | Pacific Northwest National Laboratory)

“When we try to directly observe the behavior of quantum systems, like qubits, their quantum states collapse,” said Computer scientist PNNL Ang Li. Li is also a researcher for the Quantum Science Center and the Co-Design Center for Quantum Advantage, two of the Department of Energy’s five national quantum information science research centers. “To circumvent this problem, we use simulations to study qubits and their interaction with the environment.”

Li and his collaborators at Oak Ridge National Laboratory and Microsoft use high-performance computing develop simulators that mimic real quantum devices to run complex quantum circuits. Recently, they combined two different types of simulations to create the northwest quantum simulator (NWQ-Sim) to test quantum algorithms.

“Testing quantum algorithms on quantum devices is slow and expensive. Also, some algorithms are too advanced for current quantum devices,” Li said. “Our quantum simulators can help us look beyond the limitations of existing devices and test algorithms for more sophisticated systems.”

Algorithms for quantum computers

Nathan Wiebe, co-appointed by the University of Toronto PNNL and affiliate professor at the University of Washington, takes another strategy with write code for quantum computers. Although it can sometimes be frustrating to be limited by the capabilities of current quantum devices, Wiebe sees this challenge as an opportunity.

“Noisy quantum circuits produce errors in calculations,” Wiebe said. “The more qubits a calculation takes, the more error prone it is.”

Wiebe and his collaborators at the University of Washington developed new algorithms to correct these errors in certain types of simulations.

“This work provides a cheaper and faster way to perform quantum error correction. This potentially brings us closer to demonstrating a computationally useful example of a quantum simulation for quantum field theory on short-term quantum hardware,” Wiebe said.

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Source: Sara Wong, PNNL

Sharon D. Cole