Like
Schrödinger’s cat, a 2019 claim of quantum supremacy seems to be simultaneously
alive and dead. Thanks to the rules of quantum mechanics, the fabled feline
occupies two contradictory states at once, and the same applies to this year’s
most prominent quantum advance.

In October, researchers from Google claimed to have achieved
a milestone known as quantum supremacy. They had created the first quantum
computer that could perform a calculation that is impossible for a standard
computer. But IBM researchers countered that Google hadn’t done anything
special. The clash highlights the intense commercial interest in quantum
computing, as companies jostle for position at the forefront of the field.

“It’s obviously a pissing contest,” says quantum physicist
Simon Devitt of the University of Technology Sydney.

IBM, for instance, has made a fleet of 14 quantum computers
accessible via the cloud. The largest has 53 qubits — the quantum version of
the bits found in everyday computers. Google’s latest quantum computer,
Sycamore, also has 53 qubits. Among the others vying for a piece of the quantum
action are Intel, Microsoft and Chinese companies Alibaba and Baidu.

Eventually, those companies expect, quantum computers could leave standard computers in the dust on a variety of problems, such as database searches, chemistry calculations and machine-learning tasks. And one day, perhaps decades from now, quantum computers with many millions of qubits could undermine the widely used encryption technique based on factoring very large numbers (SN: 7/8/17 & 7/22/17, p 28).

Anyone with a sufficiently powerful quantum computer could then steal credit card numbers and other sensitive data sent over the internet. As a result, we may need to use new quantum techniques to keep our information safe (SN: 10/15/16, p. 13).

Google researchers reported a demonstration of quantum computing’s power in the Oct. 24 Nature. Sycamore took only 200 seconds to perform a calculation that the researchers estimated would have taken a state-of-the-art supercomputer 10,000 years to compute (SN Online: 10/23/19). But IBM hit back with a paper suggesting an improved supercomputing technique that could theoretically perform the task in just 2.5 days. That’s still a serious chunk of computing time on the world’s most powerful computer, but not unattainable.

“It’s obviously a pissing contest.”

Simon Devitt

Whether Google’s result fully qualifies as quantum supremacy
depends on whom you ask. Some researchers are awaiting computers with more
qubits, which could make a more clear-cut demonstration. Still, the result
reveals a new level of control. Qubits tend to be error-prone, allowing
mistakes to slip into calculations. Google’s team had to coax a large number of
delicate qubits to behave all at once.

“What I think is most significant about what the Google
group achieved is they built a really good piece of hardware,” says theoretical
physicist John Preskill of Caltech. “It’s a testament to how the technology has
been advancing.”

Google researchers plan to continue increasing the number
and performance of qubits in their quantum computers, solidifying their toehold
in the quantum supremacy regime. And the team is now setting its sights on
another goal: a technique known as quantum error correction that would tame the
mistakes that do slip through. By combining several qubits into one effective
qubit, researchers could detect when an error occurs and fix it. “We’re
definitely on the road to do that with this result,” Google researcher John
Martinis said October 23 in a news conference announcing the company’s quantum
supremacy result.

Whether it’s here or just around the corner, quantum
supremacy has been compared to the Wright brothers’ first flight at Kitty Hawk,
N.C., in 1903. Airplanes became a reality but weren’t practically useful — yet
the milestone still made the history books. In the same vein, quantum computers
haven’t yet achieved their revolutionary potential.

Quantum supremacy is “not going to change the world
overnight. We have to be patient,” Preskill says. But for now, he says: “Let’s
celebrate.”