The quantum supremacy
Quantum computing promises to bring about a new golden age of scientific understanding and innovation
What is a quantum computer?
A quantum computer harnesses the strange phenomena of quantum mechanics to – in theory – deliver huge leaps forward in processing power. At their most basic level, normal computers work by turning on or off millions of transistors – tiny switches – inside microchips. These are used to store and process bits (binary digits) of data, in binary code: they can be either in the off position – representing a zero – or in the on position – representing a one. Numbers, texts, photos, websites and apps: they are all made up of millions of bits in some combination of ones and zeroes. But instead of bits, quantum computers use qubits, or quantum bits.
And what is a qubit?
If a bit is essentially a tiny switch set to on or off, a qubit is vastly more complex. It is typically a particle held in a quantum state: an electron or a photon isolated in a vacuum at a temperature colder than deep space, sometimes sealed inside an electromagnetic field. A hundred years ago, the new field of quantum physics showed that, at a subatomic level, nature operates in mind-boggling ways: uncertainty rules; causes are not guaranteed to be linked to effects; particles can be in “superposition” – in two or more places or states at once. Qubits, rather than just being on or off, can also be put in superposition: meaning they are both on and off at the same time, or somewhere between the two. “Superposition is like a spinning coin,” says Amit Katwala in Wired. “If you flip it, it can either be heads or tails. But if you spin it – it’s got a chance of landing on heads, and a chance of landing on tails. Until you measure it, by stopping the coin, it can be either.” accelerate the use of artificial intelligence: Google is already using them to improve its self-driving car software. At present, supercomputers can only analyse the most basic molecules. Quantum computers, which work using the same quantum properties as the molecules they’re analysing, should be able to simulate the precise behaviour of matter. This promises to bring about a new golden age in human understanding and innovation. Pharmaceutical companies are already using them to create new drug compounds, car companies to design more efficient batteries. In the short term, though, probably the single most important area is cryptography.
Why is cryptography so vital?
At present, most encryption systems – which protect online payment systems, passwords, even military networks – rely on the difficulty of breaking down large numbers into prime numbers. This is called factoring, and even for very powerful conventional computers, it’s hard and slow: it could take thousands of years. But it’s possible that in a little more than a decade, quantum computers will be able to crack these codes relatively easily – which could put our data at risk. It’s rumoured that intelligence agencies are stockpiling reams of encrypted data in the hope that they’ll soon have quantum computers that can crack it. Being able to create “quantum-safe” encryption is a powerful incentive in the race to master the technology (see box).