Google's Quantum Supremacy Claim and the Milestone Race That Followed

The claim surfaced in a scientific paper that appeared on NASA.gov earlier that week and was then removed, Fortune reported on 20 September 2019. Fortune obtained a copy. The Financial Times first reported the news. A Google spokesperson declined to confirm the authenticity of the paper and its results. NASA did not respond immediately to a request for comment.

A source at Google familiar with the situation said NASA had accidentally published the paper early, before the team's claims could be vetted through scientific peer review. That process can take weeks or months. So the number that anchors the whole story, 200 seconds against 10,000 years, arrived in public without that review. Every quantum milestone has the same shape: a measurement, a comparison against a classical machine, and an argument about what the comparison actually means.

The 2019 paper described an experiment that sampled randomly generated numbers through a specialized scenario involving quantum phenomena. The researchers said their quantum computer beat regular computers at the task, which involved calculating the output of certain specialized circuits.

Google's machine, dubbed Sycamore, contained 53 qubits, a measure of the machine's potential power. The team had scaled back from a 72-qubit device, Bristlecone, that it had previously designed. The researchers estimated that performing the same experiment on a Google Cloud server would take 50 trillion hours, too long to be feasible. On the quantum processor, they said, it took only 30 seconds.

Two years earlier, a target of 49 qubits

The ambition was not new. In April 2017, MIT Technology Review reported that John Martinis, who led Google's quantum research group, had given himself just a few months to reach a milestone in the history of computing: a device that could perform a particular calculation beyond the reach of any conventional computer. Proof, he said, would come from a drag race between Google's chip and one of the world's largest supercomputers.

At that point Google's roughly 25-strong group had a new chip with six qubits arranged in a two-by-three configuration. Martinis said the layout showed the company's technology still worked when qubits sat side by side, as they would in larger devices. It was also a test of a manufacturing method. Qubits and the conventional wiring that controls them are made on separate chips and later bump bonded together. The approach is meant to eliminate extra control lines that can interfere with how qubits function. Google had released results from a nine-qubit chip arranged in a line, but Martinis said he would need a grid of 49 qubits for the supremacy experiment. Designs for devices with 30 to 50 qubits were already in progress.

"That process is all working," Martinis told MIT Technology Review. "Now we're ready to kind of move fast."

Not everyone treated the target as the finish line. Chris Monroe, a University of Maryland professor and cofounder of the startup IonQ, called it "an academic milestone" and added: "Afterward you still have to figure out how to make it more scalable and programmable." Martinis agreed much remained to be done, but argued the experiment could become a benchmark for anyone claiming to have a working quantum computer. He also said the target helped managers at Google, and cofounder Sergey Brin, appreciate that the technology was becoming real.

IBM's counter, and a different metric

IBM had its own announcement. On 10 November 2017, the Associated Press reported that IBM scientists had built and measured a processor prototype with 50 qubits. Dario Gil, who led IBM's quantum computing and artificial intelligence research division, said it was the first time any company had built a quantum computer at that scale. Seth Lloyd, an MIT mechanical engineering professor not involved in the research, said IBM likely still had glitches to work out but that the announcement was a sign of significant progress.

By March 2019, IBM was arguing against qubit counts as the headline measure. At the American Physical Society March Meeting, the company outlined a Quantum Volume of 16 for its Q System One, which has a 20-qubit processor, double the Quantum Volume of 8 for its existing IBM Q system. Quantum Volume is determined by the number of qubits, connectivity and coherence time, plus 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.

Gil's objection to the supremacy framing was blunt. "The experiment and the 'supremacy' term will be misunderstood by nearly all," he told Fortune, describing the work as a highly special case laboratory experiment with "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" and said a commercially viable quantum computer would require many R&D advancements. "While development is still at mile one of this marathon, we strongly believe in the potential of this technology," he said.

The Google researchers were more hopeful about the near term. "As a result of these developments, quantum computing is transitioning from a research topic to a technology that opens new computational capabilities," they wrote in the paper, adding: "We are only one creative algorithm away from valuable near-term applications."