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Quantum computers

By , 17 May 2013

Following the news that Google is buying a quantum computer, S21 answers 3 vital questions:

1. What on earth is a quantum computer?
2. How much do they cost and how long before we can all own one?
3. What will we do with them anyway?




Sci-fi gets real

I first heard about quantum computers back in 2000. It sounded like a totally crazy idea, the kind of machine that people might try to build hundreds of years in the future, along with warp drives and teleporters. But now, just over a decade later, quantum computers are a reality, and pioneering company D-Wave has already announced its second sale of a commercial quantum computer to Google's Quantum Artificial Intelligence Lab.

What is a quantum computer?

There's one thing that everyone knows about quantum physics. It's weird. Why is it weird? Because at the subatomic scale, particles like protons and electrons that make up matter don't behave like anything we are familiar with.

You could think of an electron as a tennis ball. You put a tennis ball down somewhere and later when you go to collect it, it's exactly where you left it. But electrons aren't like that. Put them down somewhere and they can literally be anywhere when you next look for them. So electrons aren't like tennis balls. Physicists often think of subatomic particles as waves, but even that doesn't help much, because the kinds of waves we're familiar with (sound waves, water waves) are spread out in space, whereas electrons are discrete lumps of matter, or quanta. If you bumped into one you'd know it wasn't a bit like a wave.

So subatomic particles aren't like tennis balls and they aren't like waves. Except that sometimes they behave exactly like tennis balls and sometimes they behave exactly like waves. But it gets weirder. Sometimes an electron can be in one energy state and sometimes it can be in a different energy state, and sometimes it can be in both states at the same time. That's very weird indeed. And most mind-bending of all is the fact that the behaviour of all subatomic particles is inherently unpredictable, no matter how accurately you take measurements of their state (position, velocity, energy, etc.)

Einstein hated this, saying, "I cannot believe that God plays dice with the universe." But it turns out that Einstein was wrong, because that's exactly how the universe does behave, as countless experiments have shown.

OK, that's quantum physics, what about quantum computers?

In a conventional computer, the basic unit of storage is the binary bit, which can store a value of 0 or 1. In a quantum computer, the equivalent unit of storage is the qubit, and it has the strange property that it can be both 0 and 1 at the same time.

That's not to say that a qubit doesn't store any real information. It does. It can store a value of 0. Or it can store a value of 1. Or it can be in a state where it stores both values simultaneously. Weird, certainly, but true.

How do quantum computers work?

Think about what a normal computer does. That's right. It plays games, shows youtube videos and posts photos of cats on Facebook. But what's it really doing at the level of bits and bytes?

Mostly what a computer does is loop over many values of a variable, stored as binary bits, performing some kind of calculation on every value the variable may store. If there are lots of values to process, the loop takes a long time.

Now think about a quantum computer. The variable, made from qubits instead of bits, can store all possible values simultaneously. That means that instead of looping millions or billions of times, the quantum computer only needs to do a single calculation. It looks at all possible answers at once and finds the right answer in a single operation.

Quantum computers are a reality

You might have trouble believing that this is possible. But scientists around the world are already building real quantum computers and a company called D-Wave has made the first commercial quantum computer. D-Wave, which has Amazon founder Jeff Bezos as one of its investors, has sold one of its quantum computers to Lockheed Martin, which is using it to create and test complex radar, space and aircraft systems, and a second computer to Google.

These first D-Wave computers cost around $15 million and fill a large room. That makes them similar to the first commercial mainframe computers built by IBM in the 1960s. But by the 1980s, IBM was selling PCs to business users all over the world and a decade later, computers were portable and used in the home. Perhaps 10 years from now, quantum computers will be commonplace.

D-Wave's computers need to be cooled almost to absolute zero (-273° C). That makes them impractical to have in your house. But as more and more computing moves to the cloud, this isn't going to prevent the masses from making use of them. As internet connectivity becomes ubiquitous, anyone could access the power of a cloud-based quantum computer from a mobile device. And as the cost falls, we'll probably all have access to this power within a decade or two. The cost of access might eventually be free for the end user.

Quantum computers may change everything

It's undeniably true that computers have transformed our world. What might quantum computers do? The answer is that we can barely imagine what might be possible.

Lockheed Martin has been using a D-Wave One machine for about a year to study complex problems that are impossible to compute with a conventional supercomputer. Now Google has teamed up with NASA to buy a D-Wave Two. Google plans to use this on machine learning problems, creating an artificial intelligence that learns from real world data.

At present, known applications of quantum computers are limited. They can solve certain classes of problems much, much faster than classical computers. As companies like Google and Lockheed Martin work with manufacturers like D-Wave, IBM, HP and Microsoft, the number of problems that can be solved will grow.

To put this in perspective, the D-Wave Two machine uses just 512 qubits to perform its calculations, and yet it can outperform supercomputers with millions of gigabytes of memory. Imagine what could be done with a scaled-up quantum supercomputer. And the beauty is that the harder the problem you give it, the faster the quantum computer will be, compared with a classical supercomputer. So things that are simply impossible now could become easy.

At present, it's likely that quantum computing will be used for government and scientific problems like machine learning and cryptography. Suggested areas of research include facial recognition, voice recognition, medical research and climate research. But in the long term these machines have the potential to transform our world utterly.

About the author: Steve Morris studied theoretical physics at the University of Oxford before deciding to apply himself to harder questions like what is the best smartphone? and are LED TVs better than plasma?

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Comment by Charles from England on 11th Dec 2013
When these awesome computers become self aware they will take over the world, and hopefully they'll be kind to their makers.

Comment by lee from england on 17th May 2013
Just wait till Samsung get hold of one ! ;)


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