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What could the NSA do with a quantum computer?

After many false starts it’s a research field that is just now coming of age - when harnessed, particles can perform staggeringly powerful computation.

A new NSA data centre in Bluffdale, Utah. Photograph: Getty Images

The news that the US National Security Agency has been spying on public emails, phone calls and internet chat logs provokes an obvious question: just how much data can the NSA cope with? That depends on whether it has a working quantum computer.

A report leaked to the Guardian suggests that the NSA can get three billion pieces of information a month from computer records alone. Much has been made of how it would take ridiculous amounts of computer time to analyse it all. But that is exactly why the NSA, GCHQ and almost every other security agency in the world have spent the past two decades with one eye on a select group of physicists who could soon make the supercomputers of today look like children’s toys.

A standard “classical” computer stores information as a series of zeroes and ones on the microchips of its circuitry. A 0 is represented by the absence of electrical charge on a component called a capacitor. The presence of charges gives a 1. By moving the charges around between components in welldefined ways, you can represent any number you want and perform any computation.

The quantum computer uses a single atom or electron, rather than a bulky electrical charge, as the 0 or 1. In fact, the particle can be 0 and 1 at the same time. In certain conditions, atoms and subatomic particles can be in two places at once, or spin clockwise and anticlockwise at the same time. That means you can use a single atom to represent two binary digits.

Then there’s entanglement, another phenomenon of the subatomic world. This allows you to link many of the doubleheaded particles to create a string of binary digits that can simultaneously represent a huge array of numbers. A string of just 250 particles is enough to encode, simultaneously, more numbers than there are atoms in the known universe. Put those particles together in the form of a computer, and they can perform a staggeringly powerful computation on all these possible numbers at once.

So far, researchers have identified two applications for quantum computing. The first is a kind of reverse multiplication known as factorisation. This allows you to discover which numbers multiply each other to create any given number. It sounds trivial, but if the bigger number is big enough, no normal computer can do this in a reasonable time. The difficulty of factorisation is the mainstay of all data security, from military intelligence to financial transactions. So, a quantum computer is a game-changer.

The second application seems even more esoteric at first glance. It is a reverse telephonebook search: given a number, it can do the equivalent of finding a name, and much more quickly than any machine we have now. It is a way of sifting through unsorted data efficiently – just what the NSA needs.

And after many false starts it’s a research field that is just now coming of age. The first working, commercial quantum computer was created by DWave Systems, a firm based in Vancouver, Canada. Its first sale, in May 2011, was to the defence company Lockheed Martin, which has links with the NSA.

A major investor in D-Wave is In-Q-Tel, the business arm of the CIA, which “delivers innovative technology solutions in support of the missions of the US intelligence community”. IQT believes its customers can benefit from the promise of quantum computing because the intelligence world faces “many complex problems that tax classical computing”, according to Robert Ames, an IQT vice-president. He made that statement in September last year. Now we know just what he meant.