Google accidentally made computer science history last week. In recent years the company has been part of an intensifying competition with rivals such as IBM and Intel to develop quantum computers, which promise immense power on some problems by tapping into quantum physics. The search company has attempted to stand out by claiming its prototype quantum processors were close to demonstrating “quantum supremacy,” an evocative phrase referring to an experiment in which a quantum computer outperforms a classical one. One of Google’s lead researchers predicted the company would reach that milestone in 2017.

Friday, news slipped out that Google had reached the milestone. The Financial Times drew notice to a draft research paper that had been quietly posted to a NASA website in which Google researchers describe achieving quantum supremacy. Within hours, Democratic presidential candidate Andrew Yang was warning that Google’s quantum computers could break encryption, and quantum computing researchers were trying to assure the world that conventional computers and security are not obsolete.

Experts are impressed with Google’s feat. John Preskill, a Caltech professor who coined the term "quantum supremacy" in 2011, calls it a ”truly impressive achievement in experimental physics.” But he and other experts, and even Google’s own paper, caution that the result doesn’t mean quantum computers are ready for practical work.

“The problem their machine solves with astounding speed has been very carefully chosen just for the purpose of demonstrating the quantum computer’s superiority,” Preskill says. It’s unclear how long it will take quantum computers to become commercially useful; breaking encryption—a theorized use for the technology—remains a distant hope. “That’s still many years out,” says Jonathan Dowling, a professor at Louisiana State University.

Google’s conventional computers may have outed the work of its quantum computers. Dowling says he and other researchers got word of the claimed breakthrough last week after a Google Scholar alert pointed them to the draft paper. The company is collaborating with NASA, which may have posted it as part of a pre-publication review process. Google declined to comment. NASA did not respond to a request for comment.

Google and others are working on quantum computers because they promise to make trivial certain problems that take impractically long on conventional computers. The approach seeks to harness the math underpinning quantum mechanical oddities such as how photons can appear to act like both waves and particles simultaneously. In the 1990s, researchers showed this could provide a powerful new way to crunch numbers. Interest in the field spiked after a Bell Labs researcher authored an algorithm that a quantum computer could use to break long encryption keys, showing how the technology might leapfrog conventional machines.

LEARN MORE The WIRED Guide to Quantum Computing

More recently, academic and corporate researchers have built prototype quantum processors and touted use cases in chemistry and machine learning. Those devices can work on data today, but they remain too small and error-prone to challenge conventional computers for practical work. Preskill coined the term quantum supremacy in a 2011 talk considering how researchers could prove quantum hardware did in fact offer benefits over classical computers.

Google, IBM, Intel, Microsoft, and several startups have boosted investment in quantum computing significantly since then. That’s made the moment of quantum supremacy feel inevitable. “This is something we expected maybe sooner than later,” Dowling says.

One reason for that expectation was Google’s own researchers saying as much. In 2017, John Martinis, who leads the company’s quantum hardware research, predicted his team would achieve supremacy by the end of that year. Google, IBM, and Intel have all displayed quantum processors with around 50 qubits, devices that are the building blocks of quantum computers, around the size experts expected would be needed to demonstrate quantum supremacy.