Secret international discussions have resulted in governments across the world imposing identical export controls on quantum computers, while refusing to disclose the scientific rationale behind the regulations. Although quantum computers theoretically have the potential to threaten national security by breaking encryption techniques, even the most advanced quantum computers currently in public existence are too small and too error-prone to achieve this, rendering the bans seemingly pointless.

The UK is one of the countries that has prohibited the export of quantum computers with 34 or more quantum bits, or qubits, and error rates below a certain threshold. The intention seems to be to restrict machines of a certain capability, but the UK government hasn’t explicitly said this. A New Scientist freedom of information request for a rationale behind these numbers was turned down on the grounds of national security.

France has also introduced export controls with the same specifications on qubit numbers and error rates, as has Spain and the Netherlands. Identical limits across European states might point to a European Union regulation, but that isn’t the case. A European Commission spokesperson told New Scientist that EU members are free to adopt national measures, rather than bloc-wide ones, for export restrictions. “Recent controls on quantum computers by Spain and France are examples of such national measures,” they said. They declined to explain why the figures in various EU export bans matched exactly, if these decisions had been reached independently.

A spokesperson for the French Embassy in London told New Scientist that the limit was set at a level “likely to represent a cyber risk”. They said that the controls were the same in France, the UK, the Netherlands and Spain because of “multilateral negotiations conducted over several years under the Wassenaar Arrangement”.

“The limits chosen are based on scientific analyses of the performance of quantum computers,” the spokesperson told New Scientist. But when asked for clarification on who performed the analysis or whether it would be publicly released, the spokesperson declined to comment further.

The Wassenaar Arrangement is a system adhered to by 42 participating states, including EU members, the UK, the US, Canada, Russia, Australia, New Zealand and Switzerland, that sets controls on the export of goods that could have military applications, known as dual-use technologies. Canada has also implemented identical wording on 34 qubits into a quantum computer export ban.

New Scientist wrote to dozens of Wassenaar states asking about the existence of research on the level of quantum computer that would be dangerous to export, whether that research has been published and who carried it out. Only a few responded.

“We are closely observing the introduction of national controls by other states for certain technologies,” says a spokesperson for the Swiss Federal Department of Economic Affairs, Education and Research. “However, existing mechanisms can already be used to prevent in specific cases exports of such technologies.”

“We are obviously closely following Wassenaar discussions on the exact technical control parameters relating to quantum,” says Milan Godin, a Belgium adviser to the EU’s Working Party on Dual-Use Goods. Belgium doesn’t appear to have implemented its own export restrictions yet, but Godin says that quantum computers are a dual-use technology due to their potential to crack commercial or government encryption, as well as the possibility that their speed will eventually allow militaries to make faster and better plans – including in relation to nuclear missile strikes.

A spokesperson for the German Federal Office for Economic Affairs and Export Control confirmed that quantum computer export controls would be the result of negotiations under the Wassenaar Arrangement, although Germany also doesn’t appear to have implemented any restrictions. “These negotiations are confidential, unfortunately we cannot share any details or information about the considerations of this control,” says the spokesperson.

Christopher Monroe, who co-founded quantum computer company IonQ, says people in the industry have noticed the identical bans and have been discussing their criteria, but he has no information on where they have come from.

“I have no idea who determined the logic behind these numbers,” he says, but it may have something to do with the threshold for simulating a quantum computer on an ordinary computer. This becomes exponentially harder as the number of qubits rises, so Monroe believes that the rationale behind the ban could be to restrict quantum computers that are now too advanced to be simulated, even though such devices have no practical applications.

“The fallacy there is that just because you cannot simulate what the quantum computer is doing doesn’t make it useful. And by severely limiting research to progress in this grey area, it will surely stifle innovation,” he says.