By Michael Irving

A diagram of an optical circuit, where photons (red) are sent through a maze of beam splitters and mirrors and a quantum computer like Jiuzhang calculates the output

Researchers in China claim to have achieved quantum supremacy, the point where a quantum computer completes a task that would be virtually impossible for a classical computer to perform. The device, named Jiuzhang, reportedly conducted a calculation in 200 seconds that would take a regular supercomputer a staggering 2.5 billion years to complete.

Traditional computers process data as binary bits – either a zero or a one. Quantum computers, on the other hand, have a distinct advantage in that their bits can also be both a one and a zero at the same time. That raises the potential processing power exponentially, as two quantum bits (qubits) can be in four possible states, three qubits can be in eight states, and so on.

That means quantum computers can explore many possibilities simultaneously, while a classical computer would have to run through each option one after the other. Progress so far has seen quantum computers perform calculations much faster than traditional ones, but their ultimate test would be when they can do things that classical computers simply can’t. And that milestone has been dubbed “quantum supremacy.”

Last year, Google was the first to claim it had cracked quantum supremacy. The company said that its 53-qubit Sycamore processor had performed a certain computation within 200 seconds – a task that Google estimated would have taken the world’s most powerful supercomputer 10,000 years.

And now China claims to have joined the quantum supremacy club. The Jiuzhang computer reportedly found the solution to a particularly challenging problem within three minutes and 20 seconds. A traditional supercomputer, on the other hand, would take no less than 2.5 billion years to do the same – for reference, that’s more than half the current age of the Earth.

The calculation was what’s known as boson sampling, which computes the output of a complex optical circuit. Basically, photons are sent into the system via many inputs, and once inside they’re split by beam splitters and bounced around by mirrors. Boson sampling takes all those variables into account and calculates the possible output of this maze – an incredibly difficult task for a regular computer, but a good test for quantum computers.

In this case, Jiuzhang was working with 50 photons, 100 inputs, 100 outputs, 300 beam splitters and 75 mirrors. The computer managed to calculate a distribution sample in about as long as it takes to make a coffee, whereas Sunway TaihuLight – currently the fourth most powerful supercomputer in the world – would have needed a fifth of the entire age of the universe to do the same job.

That’s clearly a huge achievement, but it doesn’t mean that traditional computers are going anywhere any time soon. These kinds of calculations aren’t particularly useful work in themselves – they’re mostly tests to show off the potential power of quantum computers. Plus, they still have some stability issues that need addressing, and won’t necessarily be better at everything than their predecessors.