Google's quantum supremacy claim: 200 seconds versus 10,000 years

Fortune obtained a copy of Google's paper after it briefly appeared on NASA.gov and was then taken down. A Google spokesperson declined to confirm the authenticity of the paper and its results. NASA did not immediately respond to a request for comment, Fortune reported on 20 September 2019.

According to the paper, Google's processor took about 200 seconds to sample one instance of a quantum circuit 1 million times. A state-of-the-art supercomputer would need approximately 10,000 years to perform the equivalent task, the researchers wrote. The same experiment on a Google Cloud server would take 50 trillion hours, they estimated. On the quantum processor, it took 30 seconds.

"Quantum speedup is achievable in a real-world system and is not precluded by any hidden physical laws," the researchers wrote. They also predicted that quantum computing power will "grow at a double exponential rate," faster than the exponential rate that defined Moore's Law.

Sycamore, Bristlecone and the numbers behind the claim

The machine, dubbed Sycamore, contained 53 qubits. The team scaled back from a 72-qubit device called Bristlecone that it had previously designed. The experiment sampled randomly generated numbers produced through a specialized scenario involving quantum phenomena. The researchers said they determined that their quantum computer beat regular computers at the task, which involved calculating the output of certain specialized circuits.

"Quantum processors based on superconducting qubits can now perform computations...beyond the reach of the fastest classical supercomputers available today," the researchers wrote. "To our knowledge, this experiment marks the first computation that can only be performed on a quantum processor."

Fortune noted that a source at Google suggested NASA accidentally published the paper early, before the team's claims could be thoroughly vetted through scientific peer review, a process that could take anywhere from weeks to months. If the paper holds up under scrutiny, Fortune said it would herald a watershed moment in quantum science, countering doubt that some unforeseen law of nature may prevent quantum computers from operating as hoped.

The claim did not land without pushback.

Dario Gil, head of IBM Research, advised against using quantum supremacy as a metric with which to measure progress in the field. "The experiment and the 'supremacy' term will be misunderstood by nearly all," he told Fortune. Gil described the experiment as a highly special case "laboratory experiment" that has "no practical applications." He added: "Quantum computers will never reign 'supreme' over classical computers, but will rather work in concert with them, since each have their unique strengths."

Jim Clarke, Intel Labs' director of quantum hardware, called Google's update "a notable mile marker." He said that "a commercially viable quantum computer will require" many R&D advancements before becoming a reality. "While development is still at mile one of this marathon, we strongly believe in the potential of this technology," Clarke added.

How Google got here

The result follows a goal Google set out publicly two years earlier. In April 2017, MIT Technology Review reported that John Martinis, who leads Google's quantum research group, had given himself a few months to reach a milestone in the history of computing. By the end of that year, Martinis said, his team would build a device that achieves "quantum supremacy," meaning it can perform a particular calculation beyond the reach of any conventional computer. Proof would come from a drag race between Google's chip and one of the world's largest supercomputers.

"We think we're ready to do this experiment. It's something we can do now," Martinis said at the time.

One reason for his confidence was a new chip with six qubits arranged in a two-by-three configuration. Martinis said it showed the company's technology still worked when qubits were nestled side by side, as they would be in larger devices. It also tested a manufacturing method in which qubits and the conventional wiring that controls them are made on separate chips and later bump bonded together, an approach intended to eliminate extra control lines that can interfere with how qubits function.

"That process is all working," Martinis said. "Now we're ready to kind of move fast." Designs for devices with 30 to 50 qubits were already in progress, he said, and Martinis said he would need a grid of 49 qubits for the supremacy experiment.

Even then, researchers were already arguing about what the milestone would mean. "It'll be an academic milestone," said Chris Monroe, a professor at the University of Maryland and cofounder of the quantum computing startup IonQ. "Afterward you still have to figure out how to make it more scalable and programmable." Martinis agreed that much would remain to be done, but argued the experiment could become a benchmark for anyone claiming to have a working quantum computer.

By December 2017, the race had drawn a business audience. At the first Q2B conference, held at NASA Ames, representatives from automotive and airline companies, big banks, software companies and the military met with experts, entrepreneurs and professors. Gizmodo reported that Google was in the midst of fabricating its 49 or 50 qubit device that month and would begin testing in two weeks, not taking Christmas vacation delays into account, according to Martinis.

At the same event, Martinis pushed back on how progress was being sold. "Press releases always talk about quantum space race in number of qubits," he said. "It's more than just quantity, it's qubit quality."

IBM's competing milestone

Google was not alone in claiming a first. On 10 November 2017, the Associated Press reported that IBM had built and measured a processor prototype with 50 quantum bits. Dario Gil, who leads IBM's quantum computing and artificial intelligence research division, said it was the first time any company had built a quantum computer at this scale.

Seth Lloyd, an MIT mechanical engineering professor not involved in IBM's research, said it was likely IBM still had glitches to work out, but called the 50-qubit announcement a sign of significant progress.

IBM kept publishing milestones after that. ZDNET reported in March 2019 that IBM's Q System One, which has a 20-qubit processor, produced a Quantum Volume of 16, double the current IBM Q, which had a Quantum Volume of 8. IBM described Quantum Volume as a performance metric determined by the number of qubits, connectivity and coherence time, plus accounting for gate and measurement errors, device cross talk and circuit software compiler efficiency. IBM said Quantum Volume would need to double every year to reach Quantum Advantage, the point where quantum applications deliver significant advantages over classical computers, within the next decade.

Back at Google, the team framed its result as a transition rather than an arrival. "As a result of these developments, quantum computing is transitioning from a research topic to a technology that unlocks new computational capabilities," the researchers wrote. "We are only one creative algorithm away from valuable near-term applications."