For decades, physicists have theorized that quantum computers — machines that rely on interactions among subatomic particles to perform now-impossible analytical feats — could one day leap ahead of traditional computers and transform the business world.

Their potential uses sound like something out of a science-fiction novel. It has been widely suggested that functional quantum computers could cut through data encryption; predict stock market swings by analyzing millions of variables at once; improve drug development by simulating interactions of subatomic particles, or enable communications systems that work faster than the speed of light.

Even their staunchest advocates say today’s machines are, at best, years away from any practical use.

Even so, a growing start-up community is betting that a “quantum revolution” in computing will materialize sooner rather than later, and its members have raised hundreds of millions of dollars in private capital in a race to be first to market. An industry website,, lists 117 private start-ups that claim to be working on quantum technology.

Rigetti Computing, a California-based start-up, is among a handful of companies with its own quantum computer. The company announced Thursday it is acquiring QxBranch, a D.C.-based start-up that specializes in quantum-enabled software, in an all-equity transaction.

Rigetti and QxBranch have raised $119 million and $4 million, respectively, from venture capitalists.

“What this represents in quantum is that the customer readiness is emerging,” said Chad Rigetti, founder and chief executive of Rigetti Computing. “Quantum is really an opportunity for America to kind of leap ahead on computing and chip technology after globalization has led to the migration of that expertise elsewhere.”

Companies such as Rigetti are building on substantial investments in quantum science from the academic and government communities. The Washington Post reported in 2014 that the NSA was working on a “cryptographically useful quantum computer” under a $79.9 million research program called “penetrating hard targets.” The Chinese government has made quantum science investments of its own.

Start-ups like Rigetti are pursuing a slightly different goal.

Rigetti wants to offer a “full-stack” quantum computing capability to business customers, executives from both companies said in an interview this week. The company is already renting out its quantum computing capabilities to business customers for a fee, hoping their experimentation will yield commercially useful ideas. They declined to disclose financial details.

For the past five years QxBranch has been working to build the software, analytical functions and user interfaces that businesses could use to operate such machines. Where Rigetti has focused on hardware, QxBranch has built its business around how customers might use the technology. The two companies have worked together on various projects since 2015.

“Our job at Rigetti now will be to identify the end-use cases that can benefit from this technology,” QxBranch founder Michael Brett said in an interview. “That’s something that we’re only going to be able to do under one roof.”

Brett says his company’s customers have included large businesses from a range of industries, the largest being financial services. UBS Investment Bank used the company’s algorithms to experiment with analyzing the foreign exchange market, he said. And the pharmaceutical company Merck has experimented with possible optimization challenges.

Others working on quantum hardware include a Canadian tech firm called D-wave, which has sold its computers to Lockheed Martin and others, reportedly for millions of dollars each.

A College Park, Md.-based company called IonQ has raised roughly $22 million from investors including New Enterprise Associates, Amazon Web Services and the venture capital arm of Google. It recently hired Peter Chapman, formerly the engineering director at Amazon Prime, as chief executive.

David Moehring is a physicist who oversaw quantum computing research for IARPA, the intelligence community’s research and development agency. Moehring said he thinks the flourish of start-up activity is driven by public attention to quantum science from large tech companies, which provide a research and development customer base for start-ups. There are at least a dozen public companies — including Intel, Microsoft and Google — with quantum computing research programs.

“The customers are definitely getting more vocal,” Moehring said. “It’s really just a rising tide lifting everything right now.”