Hard drives for quantum computers: As complicated as they sound

You know what are great? Magnets! Magnets are awesome!

They are useful for so many things. Some we’ve known about for centuries. Others we are only discovering now.

One fairly recent use of magnets is storing information. You want to store a bunch of bits? Then get yourself a bunch of magnets. Point them one way for 0, and the other way for 1, and you are sorted.

Probably you should use pretty small magnets. If you need a gigabyte of storage space, that’s 8 billion bits. I imagine that 8 billion fridge magnets would probably not fit on your desk.

Once things get small, they usually get fragile. But not magnets. Magnets don’t take shit from anyone. When temperature comes along wiggling things around, it might convince some parts of the magnet to to point the wrong way. But not for long.

We all know what happens when magnets don’t point the same way. They get in a bit of an argument with each other, and then one loses. Unless temperature does a hell of a lot of wiggling, the parts it messes with will be on the losing side.

That’s why magnets are great. You tell them to store a 0, they’ll sit there and do it. You tell them to be a 1, they won’t get bored and start doing something else. They’ll sit there and protect your LOLcats until the end of time.

Well, for a decade or so at least.

Okay, now lets start talking about quantum.

Normal computers are yesterday’s news. Quantum computers are where it’s at. But the problem with quantum things is they don’t like to be looked at. Peek at them when you shouldn’t, and it’ll mess everything up.

There seems to be an obvious solution to this problem. We just shouldn’t look at them when we‘re not supposed to. Unfortunately, we aren’t the only prying eyes.

The planet Earth, for example, is more nosey than you might suspect. It has a magnetic field and, as any compass will tell you, likes other magnets to line up with it. Every magnet on the planet is constantly conversing with the Earth. Either they are arguing about whose direction is best, or bitching about all the other magnets pointing in unfashionable directions. Either way, the Earth knows what they are doing.

Its not just magnets that suffer from nosey neighbours. Everything does. Even when we think we are unobserved, there’s still loads of light and air and stuff bashing into us. They know our dirty secrets.

If we want to build a hard drive for quantum computers, we need to keep prying eyes out. We need to make sure that little scraps of info aren’t enough to find out anything. To get an even a single bit of Schrödinger’s LOLcat, lots of pretty in-depth interrogations will need to be carried out.

There are many ways to hide quantum information. Keeping it safe from noise at the same time is the hard part.

Magnets protect normal information through the tyranny of the majority. Each magnet is made up of many tiny magnets, which all snoop on each other and complain about anyone not toeing the line. That’s the secret of their stability, but it would be terrible for quantum information.

And that’s why we don’t have quantum hard drives…

..yet. We haven’t given up. And we already have some great ideas to force them into reality.

If you want a rundown of the progress so far, we wrote a review article (free version here). In it we talk about how why magnets aren’t quite awesome enough. But combining them with impossible particles might give us the holy grail. Or perhaps we need to bust out some fractals. Or maybe some other, equally crazy stuff. We’ll tell you the secrets of quantum hard drives before they’re cool.

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