A team in China has demonstrated that it has the world’s most powerful quantum computer, leapfrogging the previous record holder, Google.
at the University of Science and Technology of China in Hefei and his colleagues say their quantum computer has solved a problem in just over an hour that would take the world’s most powerful classical supercomputer eight years to crack, and may yet be capable of exponentially higher performance.
The problem, , involves simulating a quantum circuit and sampling random numbers from its output. This problem scales exponentially in complexity as you add more qubits to the circuit being modelled, which means that classical computers rapidly find the task unmanageably difficult as complexity is increased.
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In 2019, Google announced its Sycamore processor had achieved quantum supremacy – the name given to the point at which quantum computers can solve a problem that a classical computer would find impossible given a reasonable amount of time – using this problem as a testbed. Now Pan’s team has solved a version of the problem that is at least 100 times more challenging.
Google’s processor had 54 qubits and solved a benchmark problem in just 3 minutes and 20 seconds. The Google team claimed it would take the world’s most powerful supercomputer 10,000 years to crack this version of the problem, though IBM later claimed that its classical supercomputer could have solved it in two and a half days but, crucially, didn’t demonstrate that in practice.
The Chinese team’s Zuchongzhi processor – named after 5th century mathematician Zu Chongzhi, who calculated pi to a precision that wouldn’t be bettered for 800 years – has 66 qubits, but the team only used 56 of them in the experiment, solving the problem in about 70 minutes. The researchers say in their paper that this makes it an “unambiguous” display of quantum supremacy, but declined to speak to żěè¶ĚĘÓƵ. Google also declined to comment.
The concept of quantum supremacy is somewhat of a moving target because classical computers are always improving. But while Moore’s law, an industry rule-of-thumb which states that classical computers will double in transistor density every two years, has begun to slow after decades of progress, quantum computers are progressing rapidly.
at Imperial College London says that the research is an impressive step forward and that the number of qubits in cutting edge quantum computers seems to be increasing exponentially. That will bring about rapid gains given that the growth of performance also grows exponentially as each qubit is added.
“I’m very excited by this. What this has done is really demonstrate what we’ve always thought we knew, but didn’t have proved experimentally, that you can always beat a classical machine by adding a few more qubits,” he says.
“So if you think about Moore’s law, building better performing computers, all the quantum machine has to do is just add a handful of qubits,” he says. “There’s a quantum Moore’s law as well, which means the number of qubits is increasing exponentially.”
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