Study reveals quantum computers' potential to outperform classical counterparts today

By Charles Carter, 16/06/23

IBM’s quantum computer is housed inside a cryogenic container (center) surrounded by a tangle of cables used to control and read out its qubits. (Photo credit: IBM)

Despite the current challenges surrounding quantum computers, which are prone to errors and noise, a recent study suggests that these machines can still provide valuable contributions to computational tasks today.

Scientists from IBM Quantum, the University of California, Berkeley, and Lawrence Berkeley National Laboratory published their findings in the journal Nature, revealing that a 127-qubit quantum computer, in a specific calculation, outperformed a state-of-the-art supercomputer.

The researchers emphasized that the chosen calculation wasn’t intentionally difficult for classical computers but rather representative of the type of calculations physicists routinely undertake.

AN INTERIOR VIEW OF THE CRYOSTAT THAT COOLS THE IBM EAGLE, A UTILITY-SCALE QUANTUM PROCESSOR CONTAINING 127 QUBITS. UTILITY SCALE IS A POINT AT WHICH QUANTUM COMPUTERS COULD SERVE AS A SCIENTIFIC TOOL TO EXPLORE A NEW SCALE OF PROBLEMS THAT CLASSICAL METHODS MAY NOT BE ABLE TO SOLVE. CREDIT: IBM RESEARCH

This crucial test aimed to determine if today’s noisy and error-prone quantum computers can produce accurate results for common calculations, even without robust error correction.

To everyone’s surprise, the quantum computer consistently produced correct solutions as the complexity of the calculation increased, while the supercomputer algorithm faltered and provided an incorrect answer.

This outcome provides hope that quantum computing algorithms with error mitigation techniques, rather than error correction, can tackle cutting-edge physics problems.

Specifically, this breakthrough offers insights into understanding the quantum properties of superconductors and novel electronic materials.

“We’re entering the regime where the quantum computer might be able to do things that current algorithms on classical computers cannot do,” said Sajant Anand, a study co-author and graduate student at UC Berkeley.

Sarah Sheldon, senior manager for Quantum Theory and Capabilities at IBM Quantum, added, “We can start to think of quantum computers as a tool for studying problems that we wouldn’t be able to study otherwise.”

Interestingly, the success of the quantum computer’s performance has the potential to inspire improvements in classical algorithms.

According to co-author Michael Zaletel, UC Berkeley associate professor of physics, understanding how the quantum system functions might guide the development of more effective classical approaches.

The study’s key innovation lies in quantum error mitigation, a technique that addresses the noise inherent in quantum computations.

Exploded view of the 127-qubit IBM Quantum Eagle quantum processor, showing the individual circuits that serve as qubits in quantum calculations. (Image credit: Carl De Torres of StoryTK for IBM)

The IBM researchers intentionally increased the noise in their quantum circuit to estimate what the computer’s answer would be without noise. This process relies on a comprehensive understanding of the noise affecting quantum circuits and how it impacts the final output.

While noise remains a significant challenge due to the sensitivity of qubits, scientists hope to develop fault-tolerant error correction using additional qubits to monitor and rectify errors.

However, this approach presents substantial engineering obstacles, leaving its scalability uncertain.

By demonstrating the effectiveness of error mitigation, IBM’s research team has opened up new possibilities for immediate quantum computing applications.

While the path to practical quantum computers still demands further exploration, these findings represent a significant step toward harnessing the true potential of quantum computing and propelling advancements in various scientific fields.

Anand and Zaletel’s work was supported by the U.S. Department of Energy under an Early Career Award (DE-SC0022716). Wu’s work was supported by a RIKEN iTHEMS fellowship.

Cori is part of the National Energy Research Scientific Computing Center (NERSC), the primary scientific computing facility for the Office of Science in the U.S. Department of Energy.