Quantum Computing for the Mildly Curious

Maybe, like us, you’ve heard about quantum computing and you think it sounds interesting but you’re still not sure how it works or what it means. Quantum-anything is hard right?

Turns out this isn’t true. We spent the last few weeks digging around in some of the more obscure corners of the internet, and discovered that the problem isn’t conceptual. The problem is that perhaps more any other subject in tech journalism and popular science, most of what’s written about quantum computing turns out to be bullshit.

Here’s the standard explanation:

In regular computing, we rely on lots of little switches called bits. A bit has a binary value, either 0 or 1, and when you combine lots of bits together you can store data and execute instructions. This is the stuff that makes your mobile phone go beep. In quantum computing, the switches are different. Instead of representing just a 1 or 0, as conventional processors do; they represent multiple values simultaneously. Here for example, is an explanation from the Prime Minister of Canada…

Very simply, normal computers work, either there’s power going through a wire or not — a one, or a zero. They’re binary systems. What quantum states allow for is much more complex information to be encoded into a single bit…a quantum state can be much more complex than that, because as we know, things can be both particle and wave at the same time.

This ambiguity, the ability of qubits to both ‘be’ and ‘not be’ is based on a quantum effect called superposition (sort of like the stuff you’ve heard about dead cats). There’s also a second quantum effect called entanglement, which allows you to link all the qubits together. When you put them all in state of superposition and entangle them, the spin of one affects the spin of all the others. Even if placed at opposite ends of the universe, a change in one entangled qubit would mean the others would dance in instantaneous perfect unison. Einstein called this “spooky action at a distance.”

When you arrange qubits this way, you can perform many calculations at the same time. A regular computer tries to solve a problem the same way you might try to escape a maze, trying every possible corridor, turning back at dead ends, until you eventually find the way out. But a quantum computer can try all the paths at once — in effect, finding the shortcut. The reason this is exciting is because the possibilities get really crazy, very quickly. If you linked a mere 1,000 qubits in a superposition that would allow you to represent every number from 1 to 10^300. The known universe has around 10^78 to 10^82 atoms in it.

At this point, our minds all start exploding.

It’s also where journalists start getting lazy. Cue breathless predictions about how quantum computers might give us whizzy new phones, improve weather forecasting, end traffic jams, allow us to simulate consciousness and solve world peace. Unfortunately 99% of this stuff is hype and it drives real world quantum computing engineers nuts.

The problem comes when you try to measure what’s going on with the qubits — when you open the box with the cat in it. Imagine a street hustler playing the cups and ball game, except instead of three cups, she has 1,000, and instead of a ball, each cup contains either a peanut or a cashew. When the cups are all face down there could be any combination inside them, and their fates are all linked. They’re in a state of superposition.

However, that also means that as soon she lifts one cup to reveal what’s underneath, it’s like banging her fist on the table; all the other cups fall over too. Sure, you’ve got a huge list of possible combinations — but you can only access the list by making a measurement, which is a destructive event that produces just a single random outcome. In which case, you may as well use a normal computer or even just flip a coin.

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