March 23, 2026 by Sam Jarman, Phys.org
Collected at: https://phys.org/news/2026-03-quantum-fundamental-limit.html
The performance of quantum computers could cap out after around 1,000 qubits, according to a new analysis published in the Proceedings of the National Academy of Sciences. Through new calculations, Tim Palmer at the University of Oxford has reconsidered the mathematical foundations underlying the quantum principles behind the technology, concluding that restrictions on the information-carrying capacity of large quantum systems could make their computing power far more limited than many researchers predict.
Infinite potential?
For some time, quantum physicists have been growing increasingly excited—and concerned—about the seemingly limitless potential of quantum computers. In a classical computer, information content generally grows linearly as the number of bits increases. But in a quantum computer, each extra qubit doubles the number of quantum states the system can occupy.
Since these states can encode multiple possibilities at the same time, the overall system appears to become exponentially more powerful with each added qubit—at least according to our current understanding of quantum mechanics.
As technology improves and new quantum devices emerge featuring ever larger numbers of qubits, the potential growth in computing power has therefore seemed practically unbounded.
Considering Hilbert space
Through his analysis, Palmer arrives at a more restrained conclusion. In his paper, he focuses on the properties of Hilbert space: an abstract mathematical framework where every possible state of a quantum system is represented as a single point. This allows researchers to describe quantum systems using the more intuitive language of geometry.
Within this picture, superpositions of quantum states correspond to new dimensions of Hilbert space. As more qubits are added, the number of these dimensions increases exponentially. According to standard quantum mechanics, a system can explore this space smoothly and continuously, spanning an enormous range of possible quantum states.
Reaching a limit
Palmer argues that the physical reality underlying this exploration may be far more discrete than the theory assumes. In his view, there is only a limited amount of physical information a system can carry—not enough to assign fully independent values to every dimension of Hilbert space as it grows. This means that while Hilbert space still expands exponentially on paper, the accessible portion of that space becomes increasingly constrained.
In this picture, quantum states can only occupy a limited, countable set of possibilities. If correct, this would impose a clear limit on the exponential scaling predicted by standard quantum mechanics. According to Palmer’s estimates, quantum computers could begin to encounter this ceiling at around 1,000 qubits—numbers already being approached by some of today’s most advanced devices.
A more restrained future
For now, the full computing power of these systems remains untested, and may still vastly exceed that of the most powerful classical computers. But under the limits Palmer proposes, their ultimate capabilities may fall short of some long-anticipated goals, such as breaking the encryption schemes that underpin much of today’s secure data transmission.
While this may ease one of the biggest concerns surrounding quantum technology, similar constraints might also apply to many of its most promising applications: from drug discovery to optimizing complex logistical networks. Ultimately, Palmer’s analysis suggests that the future of quantum computing may be far more grounded than once imagined.
Publication details
Tim Palmer, Rational quantum mechanics: Testing quantum theory with quantum computers, Proceedings of the National Academy of Sciences (2026). DOI: 10.1073/pnas.2523350123. On arXiv: DOI: 10.48550/arxiv.2510.02877
Journal information: Proceedings of the National Academy of Sciences , arXiv
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