IBM and University of Chicago researchers have announced a major milestone in quantum computing: their system performed a calculation that modern classical methods are virtually unable to replicate. Furthermore, scientists managed to obtain statistically verifiable confidence in the accuracy of the result, Phys.org reports..

Quantum advantage verified

Researchers are calling the experiment a demonstration of a key criterion for "quantum advantage" — a scenario where a quantum computer does not merely run faster than a classical one, but solves a problem beyond the practical limits of conventional computing.

Physicists have long used random circuit sampling (RCS) to benchmark quantum systems. The method forces a quantum computer to generate extremely complex sequences that become progressively harder for classical computers to reproduce.

However, a fundamental challenge arises: as calculations grow more complex, independently verifying that the quantum computer actually reached the correct output becomes increasingly difficult.

In the new experiment, researchers applied a specially designed quantum circuit architecture. This design preserves the computational complexity of RCS while simultaneously enabling error detection during computation.

According to Associate Professor Bill Fefferman of the University of Chicago, this approach increases confidence that the quantum computer is solving a genuinely hard computational problem rather than simply generating an unverifiable output.

70 logical qubits and 15 minutes of runtime

The experiment represents one of the largest demonstrations of logical quantum computing with error correction to date. Researchers successfully utilized 70 logical qubits, performing 2,415 logical two-qubit operations and 468 T-gates — operations that characterize quantum circuit complexity.

IBM's quantum computer completed the task in roughly 15 minutes. Researchers assert that leading classical simulation methods would require a practically unacceptable amount of time to compute the same problem.

Jay Gambetta, head of IBM Research, stated that the experiment marks a transition of quantum computing into an era of practical quantum advantage. In his view, the result establishes a foundation for scaling quantum systems and applying them to problems intractable for classical methods.

The study has been published as a preprint on arXiv. The authors emphasize that developing verification methods is critical for future practical applications of quantum computers: as computational complexity increases, merely demonstrating high performance will not be enough — proving that the results are genuinely trustworthy will be essential.