Quantum thinking: Cats to computers

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Quantum physics is weird. Things can be in two places at once or spinning in two different directions at the same time.

We can normally ignore this absurdity since it only happens at the microscopic scale. However, soon machines that exploit these bizarre features could revolutionise computing.

Conventional computers store and process information as bits. A bit can be a 1 or a 0. A modern computer chip has millions (even billions) of electronic switches that can either be on to represent 1 or off to represent 0. The progress in computing over the past 70 years has been to shrink and speed up these switches.

Valves in re-creation of the Colossus mark II computer The Colossus was the first electronic computer - these are valves from a recreation of the 1944 version

A quantum computer works very differently. Because it uses as its bits tiny particles , either atoms or subatomic particles, these are subject to the laws of quantum physics.

That means they can be in two states at the same time, so a quantum bit (or qbit) can be a 1 or a 0 or a 1 and a 0 at the same time. I will say that again. A qbit can be both a 1 and a zero at the same time.

So why might this revolutionise computing?

For all their amazing performance, conventional computers have their limitations. There are some problems so difficult that all the computers that have ever been built could work together and still not find the answer before the sun explodes.


As a simple example of the sort of problem we are talking about, imagine a travelling sales representative. He or she has to go to 10 different locations in a day and wants to work out which is the most efficient order to make the visits.

This is actually a huge mathematical problem, with more than 3.5 million possible combinations that each has to be worked out before the best solution can be reached. Increase the number of locations from 10 to 20 and there are more than two quintillion possible solutions (that's 2 followed by 18 zeros).

Now consider not cities, but stars. There are 300 billion solar systems in our galaxy. No surprise then that Nasa is very interested in quantum computing.

This is an example of what's called an optimisation problem and our world is awash with them. From designing the right formula for a new drug to trying to get machines to think like humans.

A quantum computer could crunch this sort of problem pretty swiftly because its qbits are able to consider all the possible answers at the same time and then pick the best answer.

D-Wave Two quantum computer at Nasa Ames A D-Wave machine has been installed at Nasa Ames Research Center in California

So how close are we to real quantum computers? Canadian company D-Wave will sell you one now. Although there is a lively debate among physicists as to whether the D-wave machine is really a quantum computer. (That debate is too technical and complex to even attempt to summarise here).

Closer to home, researchers at Oxford University have succeeded in controlling charged calcium atoms (ions) in a quantum state. At the moment, the apparatus to do this fills a basement.

Shrink this down and add a million or two more qbits and they will have a quantum computer. That, they say, is probably a decade or more away. The physicists involved in this work are very obviously excited to be at the start of a science that could fundamentally change our world.

Newsnight's David Grossman explains quantum computers (this video is not interactive)

Interactive video produced by Laura Mulholland and Dominic Bailey in conjunction with Connected Studios

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