Particles of light

“Last year Google won international acclaim when its prototype quantum computer completed a calculation in minutes that its researchers estimated would have taken a supercomputer 10,000 years. That met the definition for quantum supremacy —the moment a quantum machine does something impractical for a conventional computer.

“Thursday, China’s leading quantum research group made its own declaration of quantum supremacy, in the journal Science. A system called Jiuzhang produced results in minutes calculated to take more than 2 billion years of effort by the world’s third-most-powerful supercomputer.

“The two systems work differently. Google builds quantum circuits using supercold, superconducting metal, while the team at University of Science and Technology of China, in Hefei, recorded its result by manipulating photons, particles of light.

[…]

“The potential power of quantum computers springs from their basic building blocks, dubbed qubits. Like the bits of conventional computers, they can represent 0s and 1s of data; but qubits can also exploit quantum mechanics to attain an unusual state called a superposition that encapsulates the possibilities of both. With enough qubits it’s possible to take computational shortcuts conventional computers can’t—an advantage that grows as more qubits work together.

“Quantum computers don’t yet rule the world, because engineers haven’t been able to get enough qubits working together reliably enough. The quantum mechanical effects they depend on are very delicate. Google and the Chinese group were able to stage their supremacy experiments because they managed to corral qubits in relatively large numbers.

“Google’s experiment used a superconducting chip dubbed Sycamore with 54 qubits, cooled to fractions of a degree above absolute zero. One qubit didn’t workbroke but the remaining 53 were enough to demonstrate supremacy over conventional computers on a carefully chosen statistical problem. It’s unclear just how many good quality qubits are needed for a quantum computer to do useful work; expert estimates range from hundreds to millions…”

Text: China Stakes Its Claim to Quantum Supremacy, Wired.

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