Google last year gained international fame when its prototype quantum computer performed a calculation in minutes that its researchers estimated that it would have taken 10,000 years for a supercomputer. Which met the definition of quantum supremacy– when quantum machine does something impossible for a conventional computer.
China’s leading quantum research group made its own declaration of quantum supremacy on Thursday, in the newspaper Science. A system called Jiuzhang produced results in minutes calculated to take more than 2 billion years of effort by the third most powerful supercomputer in the world.
The two systems work differently. Google builds quantum circuits using a superconducting metal superconductor, while the team of the University of Science and Technology of China, in Hefei, recorded its result by manipulating photons, particles of light.
No quantum computer is yet ready to do useful work. But indications that two fundamentally different forms of technology can outperform supercomputers will support the hopes – and investments – of embryonic industry. Chao-Yang Lu, a physics professor at the University of Science and Technology who worked on the project, calls the milestone “a necessary step” towards a “large-scale fault-tolerant quantum computer.”
Google and its competitors, including IBM, Microsoft, Amazon, Intel, and several tall startups have all invested heavily in the development of quantum computing hardware in recent years. Google and IBM offer access to their latest prototypes on the Internet, while Microsoft and Amazon’s cloud the platforms each host an assortment of quantum hardware from others, including Honeywell.
The potential power of quantum computers derives from their building blocks, called qubits. Like the bits of conventional computers, they can represent 0s and 1s of data; but qubits can also exploit Quantum mechanics to achieve an unusual state called layering which encapsulates the possibilities of both. With enough qubits, it is possible to take computational shortcuts that conventional computers cannot – a benefit that increases as more and more qubits work together.
Quantum computers are not yet ruling the world, because engineers have not been able to get enough qubits working together reliably enough. The effects of the quantum mechanics on which they depend are very delicate. Google and the Chinese group were able to stage their experiences of supremacy because they managed to collect relatively large numbers of qubits.
Google’s experiment used a superconducting chip called Sycamore with 54 qubits, cooled to fractions of a degree above absolute zero. One qubit didn’t work, but the remaining 53 were enough to demonstrate supremacy over conventional computers over a carefully chosen statistical problem. It is not known exactly how many good quality qubits are needed for a quantum computer to do useful work; expert estimates range from hundreds to millions.
The Chinese team also used a statistical test to assert its quantum superiority, but its quantum data carriers take the form of photons traveling through optical circuits arranged on a laboratory bench, guided by mirrors. Each photon read at the end of the process can be thought of as roughly the equivalent of reading a qubit on a processor like Google’s, revealing the result of a calculation.
Researchers reported that they measured up to 76 photons from the Jiuzhang machine, but on average 43. Members wrote code to simulate the work of the quantum system on Sunway TaihuLight, China’s most powerful supercomputer and third fastest. into the world, but he couldn’t get closer. The researchers calculate that the supercomputer would have taken more than 2 billion years to do what Jiuzhang did in just over 3 minutes.
The Chinese team was led by Jian-Wei Pan, whose large research team benefited from an effort by the Chinese government to be more prominent in quantum technology. Their achievements include demonstrating the use of quantum encryption over record distances, including the use of a specially designed satellite for quantum communications at secure a video call between China and Austria. Encryption rooted in quantum mechanics is theoretically unbreakable, although in practice it could still be subverted.
One difference between Jiuzhang and Google’s Sycamore is that the photonic prototype is not easily reprogrammable to perform different calculations. Its parameters were effectively hard-coded into its optical circuits. Christian Weedbrook, CEO and founder of Toronto-based quantum computing start-up Xanadu, which also works on photonic quantum computing, says the result is still remarkable as a reminder that there are multiple viable ways to make computing work. quantum quantum numbers. “It’s a big step in photonic quantum computing,” he says, “but also good for all of us.”