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What is quantum computing and how does it work?

IBM’s quantum computer achieved 127 qubits in November (IBM)
IBM’s quantum computer achieved 127 qubits in November (IBM)

Quantum computing has long felt like a never-ending episode of Tomorrow’s World — a sci-fi future of incredibly high-performance computing that never actually arrives. Well, it’s definitely not fiction any more.

Quantum computing is here. The Ministry of Defence has its own quantum computer; businesses can rent quantum computing time from companies such as Amazon and Microsoft today; Intel — the company that likely made the processor inside the laptop on your desk — is building its own quantum processors.

What does the availability of this phenomenally high-powered hardware mean? Are we all going to be trading in our PCs for quantum computers? And how does it actually work? We’ll answer all these questions and more.

What is quantum computing in simple terms?

There’s no such thing as simple terms when it comes to quantum computing — this is brutally complex technology and it comes in many forms. But here’s the basic gist.

Conventional computers, such as the device that you’re reading this article on, process information using bits. Bits can be thought of as light switches — they’re either on or they’re off. In a computer, those two states are represented as 0 or 1. Literally every piece of data stored on your device, whether it be a Word document or a YouTube video, can be boiled down to 1s and 0s.

Quantum computers work differently. They use qubits instead of bits, which can exist in two states simultaneously — like a light switch that can be both on and off at the same time. To make matters even more mind-blowing, quantum computers can use phenomena such as entanglement to help them perform calculations. Entanglement is a mysterious connection between two or more qubits, where their state is linked despite them being physically distant from one another.

This presents both huge opportunities and terrifying risks. On the plus side, it could be that quantum computers are better able to tackle tasks such as finding a cure for cancer

It’s incredibly hard to wrap your head around these concepts, but it basically gives quantum computers a huge processing advantage over conventional computing chips because they can crack problems much faster than regular computers or servers.

The downside is quantum computers are not easy to make. Although there are working quantum computers out there in industry and academia today, we’re at the very early stages of their development. When scaled up to dozens of qubits, they can become unstable, and they generate errors that aren’t always easy to detect.

They also require a completely different approach to programming. You can’t run conventional computer software on quantum computers, there is no quantum version of Windows! (At least, not yet.) We’re only just beginning to understand how to write software for these machines and tap their vast capabilities.

Intel has launched a 12-qubit quantum dot silicon chip (Intel)
Intel has launched a 12-qubit quantum dot silicon chip (Intel)

What does quantum computing actually do?

Quantum computers excel at the really knotty computing jobs, the ones that involve a high degree of complexity, uncertainty, or randomness. They’re not going to make Excel run faster or give you an extra shot of graphical performance in Fortnite, but they are good at tackling the mammoth tasks that would normally be thrown at a supercomputer or a cloud-computing cluster.

Quantum computing’s ability to factor large numbers could completely undermine today’s encryption technologies, which underpin all of our financial transactions and secure communications

This presents both huge opportunities and terrifying risks. On the plus side, it could be that quantum computers are better able to tackle tasks such as finding a cure for cancer, or at least making much more accurate predictions about how a tumour will mutate, which could massively improve patient outcomes.

They’re well suited to modelling the behaviour of atoms, molecules, and other natural structures, which could help us get a better understanding of how the universe works or accelerate our knowledge of climate change and find more effective ways to tackle it.

There are many more mundane tasks and activities where its superior processing power could offer enormous advantages, such as in logistics, financial modelling, and the hot computing topic of the moment — machine learning and AI.

However, there are serious risks here, too. Quantum computing’s ability to factor large numbers could completely undermine today’s encryption technologies, which underpin all of our financial transactions and secure communications. Cryptography basically works on the principle that today’s computing power is too limited to crack the code within a reasonable amount of time, but a recent IBM report claimed that “quantum computing poses an existential risk to the classical computer encryption protocols” because it was theoretically capable of brute forcing its way past even the toughest of encryption standards within a day.

That’s why companies such as Google are working on “Quantum Resilient Security Keys” to ward off such a threat. The US government has already passed the Quantum Computing Cybersecurity Preparedness Act, which is designed to protect the Federal Government systems from Q-Day — the day when quantum computers can break past conventional encryption, which some predict might only be a few years away.

When will quantum computers be available?

The Ministry of Defence (MoD) has reportedly acquired the Government’s first quantum computer (John von Radowitz / PA)
The Ministry of Defence (MoD) has reportedly acquired the Government’s first quantum computer (John von Radowitz / PA)

They’re available now, although you won’t find them if you walk into a branch of Currys.

There are several different types of quantum computer built on varying technologies, and at their most extreme they’re enormous warehouse-sized beasts that need to be kept in massive refrigerators to prevent overheating.

However, quantum computers are also starting to arrive in more conventional forms. Last year, for example, the Ministry of Defence took delivery of its first quantum computer, an ORCA Computing PT-1 that stands around 4 ft 5 in tall in a regular 19-inch server rack, and doesn’t require any special cooling equipment because it can run at room temperature. At first glance, you’d struggle to tell it apart from a regular server you might find in any business.

It’s also possible to buy quantum computing power on demand, just as you might buy regular cloud computing power. Amazon and Microsoft both rent out time on quantum computers as they do with conventional servers, allowing both academics and businesses to start getting to grips with quantum computing without going to the considerable expense of acquiring their own hardware.

Quantum computers will doubtless become more widespread as the technology matures and becomes more affordable. As we mentioned earlier, chip giant Intel has seen the looming threat to its conventional chip business and has developed its own quantum research chip, called Tunnel Falls, which it’s making available to educational establishments so that they can start building their own quantum computers.

But there’s next-to-no chance you’re going to be replacing your Windows PC or Mac with a quantum computer anytime soon. Even if it is starting to appear in conventional forms, it’s still hugely expensive (that MoD computer is likely to have cost well into six figures). And even if you could afford such extravagance, there would be no consumer-grade software to run on the thing anyway. Quantum computing technology might well trickle down into the consumer space one day, but you won’t be taking the quantum leap at home for the foreseeable future.