Quantum computing is harder than herding kittens

Quantum physicists embrace uncertainty. After all, one of the fundamental principles of the field is Werner Heisenberg’s uncertainty principle which states that we cannot precisely know both the position and the speed of a particle. Conversely, governments, companies and investors tend to hate things they don’t understand. And great uncertainty surrounds recent efforts to build powerful quantum computers.

Will quantum computing rewrite the laws of computing, cryptography, logistics and materials science, as its enthusiastic proponents claim? Or are we entering a “quantum winter”, where the diabolical difficulty of building a working quantum computer leads to a collapse of confidence?

That first question has resurfaced after the recent publication of a Chinese research paper that describes a theoretical method for bypassing the most common form of encryption on the Internet by combining existing quantum and classical computing techniques. If proven, this will be the stuff of security nightmares, hastening the arrival of the so-called Q-day, when users cannot “break the internet”.

Cryptographers have long understood the risk but thought it would take the ability of quantum computing before it could happen. The standard RSA encryption method, used by many banks, governments and Internet companies, relies on the fact that although it is easy to multiply two prime numbers it is difficult to reverse the process and find the original numbers. However, in 1994 mathematician Peter Shor wrote a program that showed how this could be done on a quantum computer, although it did not exist at the time.

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The assumption was that a quantum computer would need millions of quantum bits, or qubits, to be reliable enough to be able to encrypt RSA. Even in the most optimistic scenario, that seems ten years away. The most powerful quantum computer to be publicly unveiled – IBM’s Osprey – has only 433 qubits. And the difficulty of climbing is always difficult. One Chinese researcher likened the challenge to lining up cats; you just put one in place, others are wandering around.

What is novel about the Chinese method is that it combines the emerging quantum computing power with a factoring algorithm, written by another mathematician, Claus Schnorr, for classical computing. The researchers calculated that this could work on a quantum computer with only 372 qubits.

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Western experts say that this approach may bring Q day closer. But even the authors of this paper do not know if the methodology can be scaled up, or how long it will take. “It’s possible that this algo might work on paper but it would take so long to run that it might not be a useful acceleration,” said Tim Spiller, director of Britain’s Quantum Communications Hub.

However, the Chinese paper will serve as a spur for the US National Institute of Standards and Technology, which since 2016 has been requesting and revising many post-quantum encryption techniques. There have been similar efforts to build secure quantum information networks, which are already working experimentally. Expert advice to companies is: don’t panic, move to NIST-endorsed encryption standards whenever they are adopted and avoid snake oil salesmen who offer quick fix solutions.

The latest development comes as doubts grow over whether researchers can build quantum computers strong enough to fulfill their grandiose promises. Another cautious skeptic is Sabine Hossenfelder, a German physicist and die-hard YouTuber, who says quantum computing has become oversold and “quantum winter” is coming. “It’s not going to change the world, it’s going to have great apps, and it’s going to take longer than most startups want you to believe,” he said in his latest video.

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But mixed methods can accelerate practical applications of quantum computing. Even unconventional quantum computers can help do things that classical computers can’t do on their own, such as optimizing material performance and enriching machine learning tools. “People are already using near-quantum devices for such commercial purposes,” said Josh Nunn, chief scientific officer at startup Orca Computing.

One certainty is that the future of the quantum computing industry will remain uncertain, useful and useless at the same time, as one FT reader noted. It’s always a very lopsided investment bet. As venture capitalists say, you can only lose 100 percent of your money, but sometimes when you win, you can win a hundred times.

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