PNAS study: quantum computers face hard ceiling of ~200-1000 qubits

A paper published in the Proceedings of the National Academy of Sciences proposes a revision to quantum theory that would place a strict upper bound on the power of quantum computers. The study, written by Tim Palmer of the University of Oxford, introduces a framework called Rational Quantum Mechanics, or RaQM. The framework suggests that the mathematical space underlying quantum systems is not continuous but fundamentally discrete. This new framework suggests that quantum computers may never achieve the large-scale performance needed to break modern encryption or deliver the full exponential speedups long promised by the field. The study reframes quantum mechanics as an approximation of a deeper, information-limited system. RaQM imposes a finite capacity on how much information a quantum system can encode, which translates into a maximum number of qubits that can be meaningfully entangled and used in computation. Estimates in the study suggest that limit lies between roughly 200 and 400 qubits for current technologies and may never exceed about 1,000 qubits under any physical implementation. Beyond that threshold, the theory predicts that quantum computers would lose their computational edge even if engineers succeed in building larger and more stable machines. The paper concludes that applications such as breaking 2048-bit RSA encryption may be fundamentally impossible. The implications extend to the trajectory of the quantum computing industry, which the study suggests would need to shift toward more targeted applications that operate within the proposed limits. Near-term noisy intermediate-scale quantum devices would remain useful in domains such as chemistry, materials science and optimization. The theory remains speculative, and the paper acknowledges that RaQM and conventional quantum mechanics are indistinguishable for small systems.