Computing makes a quantum leap

Quantum computers could make today's silicon-chip computers obsolete Keystone Archive

Scientists at Geneva University have made another experimental leap forward in the quest for a quantum computer. Physicists believe that such a machine could solve mathematical problems or crack secret codes millions of times faster than today's most powerful supercomputers.

In quantum theory, objects on the subatomic level can be in two places at the same time, travel in two directions and have other seemingly contradictory properties. A team of physicists at Geneva University is trying to exploit these physical phenomena.

In a groundbreaking experiment in 1997, the group showed that distant quantum particles seemed to act as a single object. The Geneva team split a single photon (or particle of light) into a pair and sent each one through fibre-optic cables to detectors, 10 kilometres apart. When the spin of one particle was changed, the other particle instantaneously made the same movement.

Professor Nicolas Gisin from Geneva says this ghosting behaviour, known as “entanglement”, distinguishes quantum physics from classical physics: “This is really a key ingredient for this futuristic quantum computer. I think entanglement is going to become an everyday word in about 10 years.”

The idea of powerful quantum computers with the potential to perform billions of times faster than any silicon-based computer is seductive, and scientists have already built basic quantum computers that can perform certain calculations.

However, building a practical machine is still years away and one of the difficulties is how to entangle a large number of quantum particles. In their latest breakthrough, Professor Gisin’s team has achieved far greater reliability in quantum entanglement.

“A major technical challenge for quantum computation is to maintain this entanglement because it is a very fragile characteristic. If you send these photons over long distances or just want to keep a memory over seconds or minutes, disturbance from the environment may reduce or destroy it.

“There have been several theories as to how to control this entanglement and make it more robust, and our experiment is the first one to demonstrate one of these ideas, the recovery of more entanglements by filtering photons.”

Professor Gisin’s team has also been working in the field of quantum cryptography, a radically new way of guaranteeing the security of optical communication based on the laws of quantum physics.

“In quantum cryptography, we encode the information in single photons in such a way that if an adversary wants to read the message, the adversary is going to destroy the message or disturb it at least and this will be immediately noticed by the legitimate users.”

Professor Gisin says quantum cryptography is relatively close to possible applications and there are already several companies thinking about commercialising it.

“Quantum computation is a more ambitious goal. It is a completely new way of processing information which has a huge potential.”

For now, the technology required to develop such a quantum computer is beyond our reach and most research in quantum computing is still very theoretical. But one day, quantum computers could replace silicon chips and space travellers could communicate between galaxies by communication based on quantum entanglement.

by Vincent Landon