The current count of quantum computers worldwide

There is no single official registry of quantum computers, so the exact number depends on how you count them. As of early 2024, somewhere between 20 and 30 quantum computers are operational or in active testing at universities, research labs, and companies around the world. This number has grown steadily over the past five years, but it remains small because building and maintaining a quantum computer is expensive and technically difficult.

The machines that get counted are usually those with at least a few dozen qubits—the quantum equivalent of a classical computer's bits. Smaller experimental systems exist in many more labs, but they are typically not included in public counts because they are proof-of-concept devices rather than machines designed to solve real problems.

The count also shifts depending on whether you include machines that are no longer in use, machines that are still being built, or machines that are available only to paying customers through cloud access. IBM, Google, and other companies have released quantum computers that researchers can use remotely, which makes the picture more complicated than a straightforward headcount.

Key Takeaways

  • Between 20 and 30 quantum computers are currently operational worldwide, though the exact number depends on how you define "operational."
  • IBM, Google, IonQ, Rigetti, and D-Wave are the companies with the most publicly known quantum systems in use or available to researchers.
  • Many quantum computers are accessible through cloud platforms rather than physically located in one place, which makes counting them difficult.
  • The number of quantum computers is growing, but progress is slow because the machines are expensive to build and require specialized informed to operate.

Who is building quantum computers

IBM has built more quantum computers than any other company and makes several of them available through its cloud platform. IBM's systems range from 5 qubits to over 400 qubits, and researchers around the world can access them remotely. Google built a 53-qubit machine called Sycamore and has continued to develop larger systems, though Google's machines are not as widely available to outside researchers as IBM's.

IonQ, Rigetti, and D-Wave are three other companies with operational quantum computers. IonQ uses trapped ions as qubits, which is a different approach from IBM and Google. D-Wave specializes in a type of quantum computer called an annealer, which is designed for optimization problems rather than general-purpose computing. Rigetti is smaller and focuses on hybrid systems that combine quantum and classical computing.

Universities and national laboratories also operate quantum computers. The University of Science and Technology of China, the Delft University of Technology in the Netherlands, and several U.S. national labs including Los Alamos and Oak Ridge have quantum systems. These are often used for research rather than commercial applications.

Why the count is hard to pin down

Quantum computers are counted differently depending on who is doing the counting. Some sources count only machines with a certain minimum number of qubits, while others count every experimental system. Some counts include only machines that are available to outside researchers, while others include proprietary systems used only by the company that built them.

The definition of "operational" also matters. A quantum computer that is actively being used to run experiments is counted differently from one that is still in the testing phase or one that is being upgraded. Some machines are shut down for maintenance or decommissioned entirely, which changes the count over time.

Cloud access adds another layer of complexity. When IBM makes a quantum computer available through the cloud, is that one machine or multiple machines? If a researcher in Japan uses a quantum computer physically located in the United States, does it count as one quantum computer or two? Different organizations answer these questions differently.

How quantum computers are measured by size

The most common way to measure a quantum computer is by the number of qubits it has. A qubit is the quantum version of a bit—the basic unit of information in a classical computer. However, the number of qubits alone does not tell you how powerful a quantum computer is. A 50-qubit machine from one company might be more useful than a 100-qubit machine from another, depending on the quality of the qubits and how well they can be controlled.

Researchers also measure quantum computers by their error rates, which describe how often qubits make mistakes during calculations. Lower error rates mean the machine can run longer, more complex calculations before the errors pile up and ruin the result. A quantum computer with fewer qubits but lower error rates might be more practical than one with more qubits but higher error rates.

Another measure is coherence time—how long a qubit can hold its quantum state before it decays. Longer coherence times allow for longer calculations. These measures together give a better picture of a quantum computer's usefulness than qubit count alone.

The difference between types of quantum computers

Not all quantum computers work the same way. IBM, Google, and Rigetti use superconducting qubits, which are tiny circuits cooled to near absolute zero. IonQ and some academic labs use trapped ions, where individual atoms are held in place by electromagnetic fields and manipulated with lasers. D-Wave uses quantum annealers, which are specialized machines designed to solve optimization problems by finding the lowest energy state of a system.

Photonic quantum computers, which use particles of light as qubits, are being developed by companies like Xanadu and PsiQuantum, though these are still mostly in the research phase. Neutral atom quantum computers, which use atoms held in optical tweezers, are being built by companies like QuEra and Pasqal.

Each approach has trade-offs. Superconducting qubits are well-understood and relatively straightforward to scale up, but they require extreme cooling. Trapped ions have very low error rates but are harder to scale to large numbers. Photonic systems might be easier to operate at room temperature but are still in early stages. The type of quantum computer matters for what problems it can solve and how practical it is to use.

What quantum computers are actually used for

Most quantum computers today are used for research and development rather than solving real-world business problems. Researchers use them to test quantum algorithms, study how quantum systems behave, and develop better ways to control qubits. Some companies are exploring quantum computers for drug discovery, materials science, and optimization problems, but these applications are still experimental.

IBM and other companies offer cloud access partly to gather data on how researchers use quantum computers and what problems they try to solve. This helps the companies understand what improvements are needed before quantum computers become practical for widespread use. It also builds a community of researchers who are learning to program quantum computers, which will be important when the machines become more powerful.

D-Wave's quantum annealers have been used by some companies for optimization problems, such as scheduling and route planning, though it is not always clear whether they provide a real advantage over classical computers. As quantum computers improve, more practical applications will likely emerge.

The timeline for growth in quantum computing

The number of quantum computers has roughly doubled every two to three years over the past decade, though this growth rate may not continue. In 2015, there were only a handful of quantum computers in existence. By 2020, the count had grown to around a dozen. By 2024, the number had reached the low twenties to low thirties, depending on how you count.

This growth is driven by increased investment from governments and private companies, improvements in qubit quality, and growing interest from researchers and businesses. However, the pace of growth is constrained by the difficulty of the engineering involved. Building a quantum computer with more qubits and lower error rates is not straightforward a matter of time and money—it requires solving hard technical problems that do not have obvious solutions.

Most experts expect the number of quantum computers to continue growing, but probably not at an exponential rate forever. At some point, growth will likely slow as the field matures and the focus shifts from building more machines to making existing machines more useful.

Frequently Asked Questions

Can I buy a quantum computer?

Not in the way you can buy a classical computer. Quantum computers are too expensive and specialized for individual purchase. However, you can access quantum computers remotely through cloud platforms offered by IBM, Amazon, Google, and other companies. These services are usually free or low-cost for research and educational use, though commercial use may have fees.

How much does a quantum computer cost?

A quantum computer can cost anywhere from millions to tens of millions of dollars to build and operate, depending on the type and size. The exact cost varies widely and is not always publicly disclosed. The cost includes not just the hardware but also the specialized cooling systems, control electronics, and skilled staff needed to maintain and operate the machine.

Will quantum computers replace classical computers?

No. Quantum computers are specialized tools designed to solve certain types of problems faster than classical computers. For most everyday tasks—browsing the web, writing documents, streaming video—classical computers are more practical and will remain so. Quantum computers will likely be used alongside classical computers for specific applications where they have an advantage.

How many qubits does a quantum computer need to be useful?

This depends on the problem being solved and the quality of the qubits. Some researchers believe that 1,000 to 10,000 high-quality qubits will be needed for practical applications in drug discovery and materials science. Others argue that useful results are possible with fewer qubits if the error rates are low enough. There is no consensus on a specific number.

Is quantum computing a scam?

No, quantum computing is real science with real progress, but it is often overhyped in the media. Some companies make exaggerated claims about what their quantum computers can do, and some investors have lost money on quantum computing startups that failed to deliver. However, the underlying physics is sound, and progress is being made, even if it is slower than some people hoped.