University of Sydney and IBM Identify Major Source of Quantum Computing Errors

Insider BriefResearchers from the University of Sydney, working with IBM, have identified and quantified important factors limiting the performance of quantum computers and demonstrated ways to overcome their impact.The findings, which improve our understanding of how errors emerge during quantum computations, could significantly advance the reliability of quantum technology.The paper has been published in Nature Communications.Project lead Professor Stephen Bartlett from the University of Sydney Nano Institute said quantum computers remain highly susceptible to ‘noise’, or external interference, and instability, making their scaling up to useful machines difficult to achieve.“Quantum computers will become even more useful if we can reliably detect and correct errors while calculations are taking place,” said Professor Bartlett, Director of Sydney Nano.“This joint project with IBM helps us understand which parts of today’s quantum hardware are introducing the most problems and where engineering improvements will have the greatest impact.”Quantum computers promise to solve certain classes of problems beyond the reach of conventional computers, including modelling complex chemical systems, designing new materials and pharmaceuticals or potentially improving optimisation problems. But their basic units of information – quantum bits or qubits – are extremely fragile and can lose information through even tiny disturbances introduced by their environments.To address this, quantum computers use error-correction systems that repeatedly check qubits for mistakes during calculations. This means some of the physical qubits in the system are being used to find errors in the qubits doing the information processing. However, those checks themselves can introduce new errors.To analyze where the errors emerged, the research team looked at the role of mid-circuit measurements. As a quantum system undergoes an operation, specific qubits are measured at intermediate stages of the operation. This measurement collapses those qubits to classical states, while allowing other qubits to maintain their coherence.Measuring these states gives immediate feedback on how to manage the overall operation.Professor Bartlett said: “This occurs many, many times during each step of the quantum computation. Each such mid-circuit measurement takes time and everything else in the operation has to ‘idle’ while the measurement is completed. This is a major stumbling block.“But we can’t get around this step – it is an essential element of quantum error correction. What we have done in this study is pin down quantitatively what kind of performance we need out of these error checks. This is vital to design systems that can scale up and work.”Using a 156-qubit IBM Quantum Heron r2 superconducting quantum processor, the researchers tested how well different error-correction methods preserved quantum information and enabled quantum logic operations.Specifically, the team investigated how to reduce the ‘idling’ noise caused by the mid-circuit measurements.By redesigning the error-correction circuitry to reduce the idling time, the researchers substantially improved performance. The revised approach increased logical qubit survival rates from below 90 percent to more than 96 percent for each error-correction cycle.The researchers also found that measurement noise is one of the dominant limitations affecting the reliability of quantum logic operations on present-day devices.Lead author Dr Robin Harper, from Sydney Nano and the School of Physics, said the research focused on understanding why error-corrected quantum operations fail.“Quantum error correction is essential for building large-scale quantum computers, but it introduces a very complex set of engineering challenges,” Dr Harper said.“We wanted to identify which physical processes were limiting performance on modern quantum devices. What we found is that the act of measuring qubits during a calculation can itself create instability.“By redesigning how those measurements are performed, we were able to significantly improve the reliability of the logical qubits.”The work is a direct outcome of the University of Sydney’s collaboration with IBM, announced in 2024, to advance quantum error correction and benchmark different approaches to fault-tolerant quantum computing. That collaboration is funded by Intelligence Research Projects Activity (IARPA), a research funding agency of the US government.It also builds on an international collaboration and talent exchange program between the University of Sydney and University College London focused on next-generation quantum technologies. Co-author Constance Lainé is a PhD student from UCL who was embedded in the Sydney Nano research group as part of the talent exchange.Professor Bartlett said the collaboration demonstrated the importance of collaborations between universities and industry in advancing quantum technologies.“Testing these ideas on advanced quantum hardware allows us to better understand the practical challenges involved in scaling up quantum computing systems,” he said.“This kind of collaboration is essential if we want to develop quantum technologies that are useful outside the laboratory.”IBM quantum scientist, co-Principal Investigator on the IARPA grant, and co-author of this research Dr Ben Brown helped design the quantum error correction benchmark that characterised the mid-circuit measurements. Before joining IBM, Dr Brown completed a postdoctoral fellowship at the University of Sydney.Professor Bartlett said the research highlights Australia’s growing role in international quantum technology through collaborations spanning academia, government and industry.TopicsShare Get the latest research, company news, and market intelligence every week. MENTIONED IN THE ARTICLEThe University of Sydney, commonly referred to as Sydney University or Sydney Uni, is a public research university situated in Sydney, Australia. Established in 1850, it holds the distinction of being Australia's oldest university and is among the six renowned sandstone universities in the country.More in Research