Magazine article New Statesman (1996)

Code-Breaking's Quantum Leap

Magazine article New Statesman (1996)

Code-Breaking's Quantum Leap

Article excerpt

On 12 February, physicists in Shanghai announced a big breakthrough. They have linked eight subatomic particles in a way that might one day allow them to break the world's most secret codes.

The link is called entanglement and it's a strange phenomenon. It occurs only in systems that follow the rules of quantum theory: things such as atoms, electrons or the particles of light known as photons. Entanglement creates links between certain of their properties. Do something to one particle and you can instantaneously change the properties of the other even if it is half a universe away.

One application of this is in "quantum computing". Quantum computers encode numbers in the properties of photons or single atoms. Thanks to the weird nature of the quantum world, if you entangle these photons or atoms, you can encode many different numbers at once. This allows researchers to use entangled particles to perform many simultaneous computations, as if they had connected lots of computers.

With the latest milestone-eight entangled photons-researchers can, in theory, perform 256 simultaneous computations. And 256 is not a number to be sniffed at.

If you could entangle 256 quantum particles, for instance, you would be able to do as many simultaneous computations as there are atoms in the universe. That is why national security agencies worry about (and sponsor) research into quantum computing. If you had a half-decent quantum computer, you would have the number-crunching power to break every encryption now in use.

Scientists don't pose a threat as yet, though. That is because the entanglement is too fragile. To perform experiments with entangled quantum particles, you have to work in isolated laboratories, usually at cryogenic temperatures. It has taken decades to get to eight entangled particles. …

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