What’s next for quantum computing

This story is a part of MIT Technology Review's What's Next series, where we look across industries, trends, and technologies to give you a first look at the future

In 2023, progress in quantum computing will be defined less by big hardware announcements than by researchers consolidating years of hard work, getting chips to talk to one another, and shifting away from trying to make do with noise as the field gets ever more international in scope.

For years, quantum computing's news cycle was dominated by headlines about record-setting systems. Researchers at Google and IBM have had spats over who achieved what-and whether it was worth the effort. But the time for arguing over who's got the biggest processor seems to have passed: firms are heads-down and preparing for life in the real world. Suddenly, everyone is behaving like grown-ups.

As if to emphasize how much researchers want to get off the hype train, IBM is expected to announce a processor in 2023 that bucks the trend of putting ever more quantum bits, or qubits," into play. Qubits, the processing units of quantum computers, can be built from a variety of technologies, including superconducting circuitry, trapped ions, and photons, the quantum particles of light.

IBM has long pursued superconducting qubits, and over the years the company has been making steady progress in increasing the number it can pack on a chip. In 2021, for example, IBM unveiled one with a record-breaking 127 of them. In November, it debuted its 433-qubit Osprey processor, and the company aims to release a 1,121-qubit processor called Condor in 2023.

But this year IBM is also expected to debut its Heron processor, which will have just 133 qubits. It might look like a backwards step, but as the company is keen to point out, Heron's qubits will be of the highest quality. And, crucially, each chip will be able to connect directly to other Heron processors, heralding a shift from single quantum computing chips toward modular" quantum computers built from multiple processors connected together-a move that is expected to help quantum computers scale up significantly.

Heron is a signal of larger shifts in the quantum computing industry. Thanks to some recent breakthroughs, aggressive roadmapping, and high levels of funding, we may see general-purpose quantum computers earlier than many would have anticipated just a few years ago, some experts suggest. Overall, things are certainly progressing at a rapid pace," says Michele Mosca, deputy director of the Institute for Quantum Computing at the University of Waterloo.

Here are a few areas where experts expect to see progress.

Stringing quantum computers together

IBM's Heron project is just a first step into the world of modular quantum computing. The chips will be connected with conventional electronics, so they will not be able to maintain the quantumness" of information as it moves from processor to processor. But the hope is that such chips, ultimately linked together with quantum-friendly fiber-optic or microwave connections, will open the path toward distributed, large-scale quantum computers with as many as a million connected qubits. That may be how many are needed to run useful, error-corrected quantum algorithms. We need technologies that scale both in size and in cost, so modularity is key," says Jerry Chow, director at IBM Quantum Hardware System Development.

Other companies are beginning similar experiments. Connecting stuff together is suddenly a big theme," says Peter Shadbolt, chief scientific officer of PsiQuantum, which uses photons as its qubits. PsiQuantum is putting the finishing touches on a silicon-based modular chip. Shadbolt says the last piece it requires-an extremely fast, low-loss optical switch-will be fully demonstrated by the end of 2023. That gives us a feature-complete chip," he says. Then warehouse-scale construction can begin: We'll take all of the silicon chips that we're making and assemble them together in what is going to be a building-scale, high-performance computer-like system."

The desire to shuttle qubits among processors means that a somewhat neglected quantum technology will come to the fore now, according to Jack Hidary, CEO of SandboxAQ, a quantum technology company that was spun out of Alphabet last year. Quantum communications, where coherent qubits are transferred over distances as large as hundreds of kilometers, will be an essential part of the quantum computing story in 2023, he says.

The only pathway to scale quantum computing is to create modules of a few thousand qubits and start linking them to get coherent linkage," Hidary told MIT Technology Review. That could be in the same room, but it could also be across campus, or across cities. We know the power of distributed computing from the classical world, but for quantum, we have to have coherent links: either a fiber-optic network with quantum repeaters, or some fiber that goes to a ground station and a satellite network."

Many of these communication components have been demonstrated in recent years. In 2017, for example, China's Micius satellite showed that coherent quantum communications could be accomplished between nodes separated by 1,200 kilometers. And in March 2022, an international group of academic and industrial researchers demonstrated a quantum repeater that effectively relayed quantum information over 600 kilometers of fiber optics.

Taking on the noise

At the same time that the industry is linking up qubits, it is also moving away from an idea that came into vogue in the last five years-that chips with just a few hundred qubits might be able to do useful computing, even though noise easily disrupts their operations.

This notion, called noisy intermediate-scale quantum" (NISQ), would have been a way to see some short-term benefits from quantum computing, potentially years before reaching the ideal of large-scale quantum computers with many hundreds of thousands of qubits devoted to correcting errors. But optimism about NISQ seems to be fading. The hope was that these computers could be used well before you did any error correction, but the emphasis is shifting away from that," says Joe Fitzsimons, CEO of Singapore-based Horizon Quantum Computing.

Some companies are taking aim at the classic form of error correction, using some qubits to correct errors in others. Last year, both Google Quantum AI and Quantinuum, a new company formed by Honeywell and Cambridge Quantum Computing, issued papers demonstrating that qubits can be assembled into error-correcting ensembles that outperform the underlying physical qubits.

Other teams are trying to see if they can find a way to make quantum computers fault tolerant" without as much overhead. IBM, for example, has been exploring characterizing the error-inducing noise in its machines and then programming in a way to subtract it (similar to what noise-canceling headphones do). It's far from a perfect system-the algorithm works from a prediction of the noise that is likely to occur, not what actually shows up. But it does a decent job, Chow says: We can build an error-correcting code, with a much lower resource cost, that makes error correction approachable in the near term."

Maryland-based IonQ, which is building trapped-ion quantum computers, is doing something similar. The majority of our errors are imposed by us as we poke at the ions and run programs," says Chris Monroe, chief scientist at IonQ. That noise is knowable, and different types of mitigation have allowed us to really push our numbers."

Getting serious about software

For all the hardware progress, many researchers feel that more attention needs to be given to programming. Our toolbox is definitely limited, compared to what we need to have 10 years down the road," says Michal Stechly of Zapata Computing, a quantum software company based in Boston.

The way code runs on a cloud-accessible quantum computer is generally circuit-based," which means the data is put through a specific, predefined series of quantum operations before a final quantum measurement is made, giving the output. That's problematic for algorithm designers, Fitzsimons says. Conventional programming routines tend to involve looping some steps until a desired output is reached, and then moving into another subroutine. In circuit-based quantum computing, getting an output generally ends the computation: there is no option for going round again.

Horizon Quantum Computing is one of the companies that have been building programming tools to allow these flexible computation routines. That gets you to a different regime in terms of the kinds of things you're able to run, and we'll start rolling out early access in the coming year," Fitzsimons says.

Helsinki-based Algorithmiq is also innovating in the programming space. We need nonstandard frameworks to program current quantum devices," says CEO Sabrina Maniscalco. Algorithmiq's newly launched drug discovery platform, Aurora, combines the results of a quantum computation with classical algorithms. Such hybrid" quantum computing is a growing area, and it's widely acknowledged as the way the field is likely to function in the long term. The company says it expects to achieve a useful quantum advantage-a demonstration that a quantum system can outperform a classical computer on real-world, relevant calculations-in 2023.

Competition around the world

Change is likely coming on the policy front as well. Government representatives including Alan Estevez, US undersecretary of commerce for industry and security, have hinted that trade restrictions surrounding quantum technologies are coming.

Tony Uttley, COO of Quantinuum, says that he is in active dialogue with the US government about making sure this doesn't adversely affect what is still a young industry. About 80% of our system is components or subsystems that we buy from outside the US," he says. Putting a control on them doesn't help, and we don't want to put ourselves at a disadvantage when competing with other companies in other countries around the world."

And there are plenty of competitors. Last year, the Chinese search company Baidu opened access to a 10-superconducting-qubit processor that it hopes will help researchers make forays into applying quantum computing to fields such as materials design and pharmaceutical development. The company says it has recently completed the design of a 36-qubit superconducting quantum chip. Baidu will continue to make breakthroughs in integrating quantum software and hardware and facilitate the industrialization of quantum computing," a spokesman for the company told MIT Technology Review. The tech giant Alibaba also has researchers working on quantum computing with superconducting qubits.

In Japan, Fujitsu is working with the Riken research institute to offer companies access to the country's first home-grown quantum computer in the fiscal year starting April 2023. It will have 64 superconducting qubits. The initial focus will be on applications for materials development, drug discovery, and finance," says Shintaro Sato, head of the quantum laboratory at Fujitsu Research.

Not everyone is following the well-trodden superconducting path, however. In 2020, the Indian government pledged to spend 80 billion rupees ($1.12 billion when the announcement was made) on quantum technologies. A good chunk will go to photonics technologies-for satellite-based quantum communications, and for innovative qudit" photonics computing.

Qudits expand the data encoding scope of qubits-they offer three, four, or more dimensions, as opposed to just the traditional binary 0 and 1, without necessarily increasing the scope for errors to arise. This is the kind of work that will allow us to create a niche, rather than competing with what has already been going on for several decades elsewhere," says Urbasi Sinha, who heads the quantum information and computing laboratory at the Raman Research Institute in Bangalore, India.

Though things are getting serious and internationally competitive, quantum technology remains largely collaborative-for now. The nice thing about this field is that competition is fierce, but we all recognize that it's necessary," Monroe says. We don't have a zero-sum-game mentality: there are different technologies out there, at different levels of maturity, and we all play together right now. At some point there's going to be some kind of consolidation, but not yet."

Michael Brooks is a freelance science journalist based in the UK.