Quantum Supremacy: How Google and IBM Turned Qubit Counts Into a Decade-Long Race

Google said it had achieved quantum supremacy, the moment when a quantum computer solves a problem beyond the practical reach of any classical machine. The company's paper, obtained by Fortune after it briefly appeared on NASA.gov, described a processor called Sycamore with 53 qubits, or quantum bits.

The number itself was not the point. By the time Google made its claim public in September 2019, the race had already produced a string of announcements built around qubit counts, wiring tricks, and error rates. Each one came with a caveat attached. "Press releases always talk about quantum space race in number of qubits," said John Martinis, the University of California, Santa Barbara physicist leading Google's effort, at the Q2B conference at NASA Ames in December 2017. "It's more than just quantity, it's qubit quality."

Two years earlier, a six-qubit test

MIT Technology Review reported in April 2017 that Martinis had given himself a few months to reach a milestone in computing history. His roughly 25-strong group at Google had built a six-qubit chip arranged in a two-by-three grid. The layout mattered. It was the first test of whether the company's qubits still worked when placed side by side, as they would need to be in a larger device.

The chip also tested a manufacturing method. Qubits and the conventional wiring that controls them are made on separate chips and later bump bonded together. Google's team had focused on that approach since the group was established just over two years earlier, according to the same report. The goal was to eliminate extra control lines that can interfere with how qubits function. "That process is all working," Martinis said at the time. "Now we're ready to kind of move fast."

At that stage, Google had demonstrated quantum computing with nine qubits arranged in a line. 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.

IBM answers with 50 qubits

IBM moved first. On 10 November 2017, the Associated Press reported that IBM scientists had built and measured a processor prototype with 50 quantum bits. 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. He called the announcement a sign of significant progress.

Google's response came a few weeks later, at the Q2B conference. Martinis said his team was fabricating a 49 or 50 qubit supremacy device that month and would begin testing in two weeks, not counting Christmas vacation delays. He also described the problem the device would solve. The team would entangle its qubits and let the system evolve over time, then measure the outcomes. Simulating those outcomes on a classical computer would take weeks. The quantum machine could do it in minutes, a gap that would demonstrate both scale and qubit quality.

Not everyone treated qubit counts as a useful scoreboard. "It'll be an academic milestone," Chris Monroe, a University of Maryland professor and cofounder of the quantum computing startup IonQ, told MIT Technology Review. "Afterward you still have to figure out how to make it more scalable and programmable."

The 2019 claim and the pushback

Google's paper said its processor took about 200 seconds to sample one instance of a quantum circuit a million times. A state-of-the-art supercomputer would need approximately 10,000 years for the equivalent task. The same experiment on a Google Cloud server would take 50 trillion hours, the researchers estimated. On the quantum processor, it took 30 seconds. "To our knowledge, this experiment marks the first computation that can only be performed on a quantum processor," they wrote.

IBM's Gil rejected the framing. "The experiment and the 'supremacy' term will be misunderstood by nearly all," he told Fortune. He described it as a highly special case laboratory experiment with no practical applications. Quantum computers, he said, would work alongside classical machines rather than reign over them. Jim Clarke, Intel Labs' director of quantum hardware, called the result a notable mile marker and said a commercially viable quantum computer would require many more advances. "While development is still at mile one of this marathon, we strongly believe in the potential of this technology," he said.

Google's own blog post, published after Nature ran the result in October 2019, mixed celebration with caution. The company traced its quantum effort to 2006, when scientist Hartmut Neven began exploring how the technology might accelerate machine learning, and noted that Martinis and his Santa Barbara team joined in 2014. It said practical applications remained many years away. It also credited a forced laboratory shutdown during the October 2018 Southern California wildfires with helping the team reset after a period when progress had slowed.

The commercial timelines stayed vague. At the American Physical Society March Meeting in 2019, IBM said its Q System One, with a 20-qubit processor, had reached a Quantum Volume of 16, double the 8 of its earlier IBM Q machine. Quantum Volume accounts for qubit count, connectivity, coherence time, gate and measurement errors, device cross talk, and compiler efficiency. IBM said the metric would need to double every year to reach Quantum Advantage within the next decade. It had doubled the power of its quantum computers annually since 2017, the company said.

ZDNET reported that practical, broad use cases were still years away. Which is roughly where the field sits. A milestone, even a genuine one, is not a product.