Test-driving a quantum computer

I’d expected to have to wait a decade or so before I could use a quantum computer. But on the contrary I can do it today. And so can you. From 4th May, technology multinational IBM is making its prototype quantum processor available for the public to use on a cloud-based platform accessible from any mobile or desktop device.

In the IBM Quantum Experience you can run experiments and algorithms that use “quantum bits” (qubits). Roughly speaking, these are like the transistor-based bits of regular computer circuits that process information as binary 1’s and 0’s, but manipulated according to the laws of quantum mechanics.

These laws make qubits immensely more versatile than the classical bits of your laptop. At any moment they can be not just in two possible states—a 1 or a 0—but in so-called superpositions of those states, such as “half 1 and half 0,” or any other combination of the two. This means that qubits have access to a much bigger range of states, and that variety allows them to perform certain tasks much more rapidly than classical bits. This is often expressed in terms of quantum computers performing many calculations in parallel whereas classical computers can only do one at a time—an over-simplification of where “quantum speedup” comes from, but adequate to give an impressionistic view of what is special about quantum computers. (When Canadian prime minister Justin Trudeau wowed the press last month with an impromptu explanation of quantum computing, he did well to keep it a bit vague.

These quantum tricks are why IBM’s quantum processor can do some impressive things using just five qubits, whereas an equivalent classical processor with five bits would be scarcely capable of even the simplest tasks. The reason this quantum circuit is so small is that it is immensely difficult to sustain quantum superpositions for significant periods of time: they are very fragile and easily destroyed by disturbances from their environment, such as heat. The more qubits you want to keep “synchronised,” the harder it is. This problem is what quantum engineers have to solve if they’re going to make quantum computers a significant commercial reality.

IBM’s qubits are made from superconducting materials, which can conduct electricity without any resistance at very low temperatures. Superconductivity is itself a quantum effect, which is why it can be used for quantum information processing.

The IBM device builds on advances in coping with errors. A big problem for quantum computation is that it’s not possible to handle the inevitable errors that crop up from time to time during the information processing in the same way as we do in classical computers, which is simply to use back-up copies of each bit. You need to find new tricks to stop errors from derailing the whole calculation. Scientists at IBM’s Yorktown Heights research centre in New York solved some of those challenges last year.

All the same, it’s going to take considerably more than a 5-qubit device to really make new kinds of computing possible. Yet IBM says that just 50 quibts would be enough to do things today’s top supercomputers can’t, and they predict that quantum processors this big will appear in the next decade.

Don’t, however, get too excited about IBM Quantum Experience until you’ve tried it. To get access, you need to fill in an online application form and then await an invitation. I’ve not yet tried it, and it’s not too clear how it will work. In the meantime, though, the site offers tutorials where you can learn more about quantum computers. It’s science that you might need to know sooner than you think.

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