Quantum computing experts are baffled by the UK government’s new export restrictions on the exotic devices, saying they make little sense. The legislation applies to both existing, small quantum computers that are of no practical use and larger computers that don’t actually exist, so cannot be exported. Instead, there are fearsĚýthe limits will restrict sales and add bureaucracy to a new and growing sector.
The came into effect on 1 April and ban the export of quantum computers with 34 or more quantum bits, or qubits, and error rates below a certain threshold. The exact error threshold depends on the number of qubits, as machines with more qubits are more capable for a given error rate. The intention seems to be to restrict machines of a certain capability, but the UK government hasn’t explicitly said this. A 91av freedom of information request to the Department for Business and Trade (DBT) for a rationale behind these numbers wasĚýturned down on the grounds of national security.
Certainly, quantum computers have the theoretical potential to threaten national security. Modern encryption algorithms that protect everything from email to bank accounts are based on mathematical problems deemed too hard to be cracked by even the fastest computers available today, but a large enough quantum computer would be able to decrypt them with ease. Such machines don’t exist yet though – even the most advanced quantum computers currently in public existence are too small and too error-prone to achieve this.
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“As far as we know, quantum computers don’t begin to threaten public-key encryption until you have millions of physical qubits, in order to encode thousands of error-corrected qubits. I can see no good reason whatsoever to impose export controls on 34-qubit devices, which have no applications at all besides scientific ones,” says at the University of Texas at Austin.
at the University of Maryland says a system with 40 qubits would be roughly equivalent to a conventional data centre with 1 trillion transistors, which may explain the origin of the 34 qubits limit. “Classical computers will not be able to fully simulate the behavior of somewhere north of 40 qubits. By choosing a number a bit less, maybe it allows a safety factor of sorts.”
But he is still unsure why this should concern the UK government, given that far more qubits will be required to crack encryption. “My best guess is ignorance. Governments get very nervous when industry pulls way ahead on a sensitive technology,” he says.
at UK-based quantum firm Orca Computing speculates that the limits may be based on calculations done by government agencies –Ěýperhaps military or security services –Ěýof what it would take to carry out certain operations that they have identified as being useful to adversaries, or they could simply be arbitrary numbers. But he says that whatever the numbers’ origin, they are well above the capabilities of current systems – although some quantum computers currently in operation have more than 34 qubits, none can match the error rates in the legislation. The low error rates across large numbers of qubits would be an “incredible feat”, he says.
“This isn’t going to affect any system that I know of today,” says Murray. “There could be systems that people don’t know about, and that’s not at all any speculation or inference on my part, it’s just the fact that you just don’t know what’s going on because big corporate labs don’t necessarily show us everything that they’re doing and certain government labs aren’t public at all with what they’re doing.”
Ultimately, Monroe sees the restrictions doing more harm than good. “The best way for the UK to play a role in future quantum computer development, including quantum hacking, is for the fledgling UK industry in this field to be unrestricted to innovate,” he says. “This ban will only ensure that any efforts to build quantum computers in the UK will fall behind others in the world.”
The DBT declined to respond to the points made by experts due to the ongoing UK general election campaign. “Unfortunately, we are unable to comment on this at the moment due to pre-election rules. We’d note that these export controls took effect on 1 April,” says a spokesperson.
