IBM Quantum Computer Solves in 15 Minutes a Problem Too Hard for Classical Methods

Researchers from IBM and the University of Chicago have demonstrated a quantum computation that they say goes beyond the practical reach of leading classical simulation methods, while also addressing a long-standing problem: how to verify that the result is correct. The team announced the demonstration on July 30, 2026, describing it as evidence that quantum computing has met the central requirements for "quantum advantage" - completing a task beyond the reach of classical methods while providing a reliable measure of how faithfully the computation was performed. The work is described in a paper posted on arXiv.

Testing whether quantum computers can outperform classical ones has long relied on a benchmark called random circuit sampling, in which a quantum computer produces patterns too complex for classical computers to recreate efficiently. But the harder the calculation, the more difficult it becomes to confirm the output is correct, and verification can become infeasible without major assumptions about the machine. The IBM and University of Chicago team designed a more structured alternative that they say preserves the same computational difficulty while letting errors be detected as the calculation proceeds. "Verification remains one of the biggest challenges in firmly establishing experimental quantum advantage," said Bill Fefferman, an associate professor at the University of Chicago.

The experiment used 70 logical qubits - units of quantum information encoded across multiple physical components to protect against noise - in one of the largest quantum error-correction demonstrations reported so far. The system completed 2,415 logical two-qubit operations and 468 logical "T gates," measures of circuit complexity, while the encoding reduced the effective logical error rate to one-tenth of the physical error rate. The computation took about 15 minutes, a runtime the researchers say leading classical simulation methods could not practically match.

"We are now firmly in the quantum advantage era," said Jay Gambetta, director of IBM Research and an IBM Fellow. Soumik Ghosh, a University of Chicago PhD student involved in the work, said advances in verification could also help unlock practical applications for future quantum computers. The circuits and results from the demonstration have been released publicly through the Quantum Advantage Tracker.