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Researchers from IBM and the University of Chicago have demonstrated a quantum computation that took about 15 minutes to complete, while leading classical simulation methods would require an impractical amount of time. The experiment also tackled a major problem in quantum computing: determining whether a difficult quantum calculation was performed accurately.

The researchers say their approach meets key requirements for demonstrating quantum advantage, meaning a quantum computer can perform a task beyond the practical reach of classical machines while providing evidence that the result is reliable. The findings were announced July 30, 2026, and described in a paper published on arXiv.

Quantum advantage has been difficult to establish because making a problem sufficiently complex to defeat classical computers can also make the quantum result nearly impossible to verify. Random circuit sampling, a common benchmark, produces outputs that are extremely difficult for classical systems to reproduce. However, checking those outputs becomes increasingly challenging as the circuits grow more complex.

The IBM and University of Chicago team developed a more structured type of encoded quantum circuit designed to preserve computational difficulty while allowing researchers to detect errors during the calculation. This gives scientists a way to estimate how faithfully the quantum system performed the computation without requiring a classical computer to reproduce the entire result.

The experiment used 70 logical qubits, which protect quantum information by encoding it across multiple physical components. The system performed 2,415 logical two-qubit operations and 468 logical T gates, while encoding reduced the effective logical error rate to one-tenth of the physical error rate.

“This experiment develops techniques to better characterize the fidelity of hard quantum states under noise,” said University of Chicago Associate Professor Bill Fefferman, adding that the method increases confidence that the quantum computer is actually solving a computationally difficult problem.

IBM Research Director Jay Gambetta described the demonstration as evidence that quantum computing has entered the quantum advantage era. The researchers have also made the circuits and results publicly available through the Quantum Advantage Tracker.

The achievement does not mean quantum computers have replaced classical machines for general-purpose computing. Instead, it demonstrates progress toward reliable, error-corrected quantum systems capable of tackling specific problems that become impractical for conventional computers.

The researchers say improved verification and error correction could ultimately help unlock practical applications as quantum processors scale. For now, the experiment represents an important step toward proving that quantum computers can not only outperform classical systems on carefully selected tasks, but also provide results that scientists can meaningfully trust.