IBM and researchers from the University of Chicago today announced a demonstration in quantum computing that achieves the fundamental criteria for quantum advantage: performing computations beyond the reach of leading classical simulation methods while providing trust that the computation returned accurate results.

In their new paper, “Sampling hard circuits with verifiably high fidelity,” the researchers showed that these two goals could be simultaneously achieved by a novel construction of encoded quantum circuits, enabling one of the largest demonstrations of logical quantum computing to date. These circuits and their results are also now openly released on the Quantum Advantage Tracker.

Building Trust into Quantum Results

For years, researchers have used a benchmark known as random circuit sampling (RCS) to test whether quantum computers could outperform classical systems. In simple terms, RCS asks a quantum computer to generate patterns so complex that a classical computer cannot efficiently reproduce them. The challenge has been verification: as the problem becomes harder, it becomes increasingly difficult and then infeasible to prove the quantum computer’s answer is correct, without making strong assumptions about the inner workings of the quantum computer.

In their experiment, researchers from IBM and the University of Chicago have addressed this obstacle with a structured alternative to RCS. The team was able to prove that this alternative retains the same hardness criteria as RCS, but crucially the new structure can be used to detect errors during the computation.

“Verification remains one of the biggest challenges in firmly establishing experimental quantum advantage,” said Bill Fefferman, Associate Professor at the University of Chicago. “This experiment develops techniques to better characterize the fidelity of hard quantum states under noise, increasing confidence that the quantum computer is solving a computationally hard problem.”

Soumik Ghosh, PhD student in Fefferman’s group at the University of Chicago, added, “Beyond strengthening experimental validation, advances in verification have the potential to unlock practical applications for the next generation of quantum computers.”

In one of the world’s largest-known error correction demonstrations, the team executed 70 logical qubits — shielding them from errors to run 2,415 logical two-qubit operations and 468 logical “T gates,” both metrics that quantify the complexity of a quantum circuit. Because the circuit was encoded, the logical computation was able to achieve effective logical error rates that were 10 times lower than the physical error rates, enabling the remarkably high circuit fidelity even at the large gate counts.

“We are now firmly in the quantum advantage era,” said Jay Gambetta, Director of IBM Research and IBM Fellow. “We have demonstrated a quantum computation beyond the practical reach of classical computers that establishes, with statistical confidence, a lower bound on how faithfully it was executed. This milestone gives scientists, developers, and businesses a new foundation for trusting quantum computers as they scale to problems far beyond what we can achieve classically.”

The team showed many leading classical simulation approaches faced prohibitive runtimes — while the IBM quantum computer took approximately 15 minutes to accomplish the task.

Error correction, and trust in the computation’s output, are essential milestones towards scaling quantum computing — and this work marks a significant step on the path forward.

More Demonstrations of Quantum Advantage Emerge

Today, alongside this milestone from IBM and the University of Chicago, partners from across IBM’s ecosystem are announcing more demonstrations of quantum advantage with trusted computations. To learn more, visit https://www.ibm.com/quantum/blog/quantum-advantage.