A Classical Laptop Just Challenged a Quantum Supremacy Claim

When D-Wave published its quantum supremacy claim in March 2025, the company said the same spin glass calculation would take a classical computer nearly a million years and consume more energy than the world uses in a year. A team at the Simons Foundation's Center for Computational Quantum Physics just published a Science paper showing a laptop can solve the same problem. The arXiv preprint of their challenge went up three weeks before D-Wave's own peer-reviewed paper cleared review.

The Simons result does not prove D-Wave's hardware is useless. It does suggest the word "supremacy" in quantum computing claims deserves more scrutiny than it usually gets.

The CCQ team used tensor networks — a mathematical framework for describing quantum states — combined with belief propagation, an algorithm from the 1980s recently adapted for quantum systems. Their result matched what D-Wave's Advantage2 processor produced. No cryogenic cooling required. No quantum hardware at all.

"We didn't set out to disprove D-Wave," said Joseph Tindall, an associate research scientist at the CCQ and first author on the new Science paper. "We wanted to know whether the dynamics they were simulating were genuinely beyond classical reach. They aren't."

The work, published in Science on May 21, 2026, also verified universal Kibble-Zurek physics across systems involving hundreds of qubits. The CCQ team calls their method scalable in both two and three dimensions, meaning the classical approach has no obvious ceiling. The code is open-source: the team used ITensor, available on GitHub.

D-Wave CEO Alan Baratz disputed the challenge when it first appeared in March 2025, saying the Simons team tested only a subset of the problems his company's study covered and didn't address all lattice geometries and conditions in the original work. Andrew King, D-Wave's director of quantum computing, ran larger calculations — up to 3200 qubits — in response, though those results have not yet been published. D-Wave did not respond to a request for comment on whether the May 2026 Science paper changes the company's position on its supremacy claim.

The gap between "quantum annealer" and "quantum computer" is where this story lives. D-Wave's Advantage2 is not a general-purpose quantum computer. It is a specialized processor that finds low-energy configurations of spin glass systems by letting a quantum system settle into its ground state naturally. Whether that counts as "quantum supremacy" depends on whether the classical alternative is genuinely hard, or just not yet well-explored.

"The time to run our algorithm scales linearly in proportion to the size of the problem," Miles Stoudenmire, a CCQ research scientist and study co-author, told New Scientist. "There is no need to test larger problems to establish that classical methods can handle this class."

Maurice Sels, a physicist at EPFL, used time-dependent variational Monte Carlo to rival quantum annealer performance on three-dimensional diamond lattice systems up to 128 spins, achieving correlation errors below 7%. Sels said the Simons result fits a broader pattern: quantum annealers solve specific optimization problems efficiently, but that efficiency does not always mean the problems are classically intractable, only that the classical competition had not caught up yet.

For anyone running quantum due diligence — a VC evaluating a quantum computing startup, a procurement team negotiating a contract, a researcher planning a roadmap — the practical implication is this: when a hardware vendor claims a problem is classically intractable, ask whether anyone has tried tensor networks with belief propagation. The Simons paper is now part of the record showing the answer may be "not yet, but it's coming." The follow-on question is whether D-Wave's unpublished 3200-qubit run, if and when it appears, closes that gap — or whether the classical tools keep closing it faster than the quantum hardware scales.