Technical quarrels between quantum computing experts rarely escape the field’s rarified community. Late Monday, though, IBM’s quantum team picked a highly public fight with Google. In a technical paper and blog post, IBM took aim at potentially history-making scientific results accidentally leaked from a collaboration between Google and NASA last month. That draft paper claimed Google had reached a milestone dubbed “quantum supremacy”—a kind of drag race in which a quantum computer proves able to do something a conventional computer can’t. Monday, Big Blue’s quantum PhDs said Google’s claim of quantum supremacy was flawed. IBM said Google had essentially rigged the race by not tapping the full power of modern supercomputers. “This threshold has not been met,” IBM’s blog post says. Google declined to comment. It will take time for the quantum research community to dig through IBM’s claim and any responses from Google. For now, Jonathan Dowling, a professor at Louisiana State University, says IBM appears to have some merit. “Google picked a problem they thought to be really hard on a classical machine, but IBM now has demonstrated that the problem is not as hard as Google thought it was,” he says. Whoever is proved right in the end, claims of quantum supremacy are largely academic for now. The problem crunched to show supremacy doesn’t need to have immediate practical applications. It's a milestone suggestive of the field’s long-term dream: That quantum computers will unlock new power and profits by enabling progress in tricky areas such as battery chemistry or health care. IBM has promoted its own quantum research program differently, highlighting partnerships with quantum-curious companies playing with its prototype hardware, such as JP Morgan, which this summer claimed to have figured out how to run financial risk calculations on IBM quantum hardware. The IBM-Google quantretemps illustrates the paradoxical state of quantum computing. There has been a burst of progress in recent years, leading companies such as IBM, Google, Intel, and Microsoft to build large research teams. Google has claimed for years to be close to demonstrating quantum supremacy, a useful talking point as it competed with rivals to hire top experts and line up putative customers. Yet while quantum computers appear closer than ever, they remain far from practical use, and just how far isn’t easily determined. The draft Google paper that appeared online last month described posing a statistical math problem to both the company’s prototype quantum processor, Sycamore, and the world’s fastest supercomputer, Summit, at Oak Ridge National Lab. The paper used the results to estimate that a top supercomputer would need approximately 10,000 years to match what Sycamore did in 200 seconds. IBM, which developed Summit, says the supercomputer could have done that work in 2 ½ days, not millennia—and potentially even faster, given more time to finesse its implementation. That would still be slower than the time posted by Google’s Sycamore quantum chip, but the concept of quantum supremacy as originally conceived by Caltech professor John Preskill required the quantum challenger to do something that a classical computer could not do at all. This is not the first time that Google’s rivals have questioned its quantum supremacy plans. In 2017, after the company said it was closing in on the milestone, IBM researchers published results that appeared to move the goalposts. Early in 2018, Google unveiled a new quantum chip called Bristlecone said to be ready to demonstrate supremacy. Soon, researchers from Chinese ecommerce company Alibaba, which has its own quantum computing program, released analysis claiming that the device could not do what Google said.
IBM has said Google’s claim of reaching the threshold of quantum computing was flawed and that it had rigged the race to the computing milestone, saying in a blog post that the threshold had not been met. Both companies, along with firms including Intel and Microsoft, have large teams working on quantum computing, and Google has long claimed to be close to achieving it, although IBM appeared to change the requirements for reaching the threshold in last month. Meanwhile, Alibaba questioned Google’s claims about its supercomputing program. Google is expected to publish a formal version of its leaked claim.