Quantum computing sees the light

Scientists have made an advance in the quest for a functional quantum computer by exploiting currently existing technology in a novel and unexpected way.

Scientists at the US Department of Energy’s Los Alamos National Laboratory and the University of Queensland’s Centre for Quantum Computer Technology in Australia have made an advance in the quest for a functional quantum computer by exploiting currently existing technology in a novel and unexpected way.

Los Alamos researchers propose to use quanta of light or photons as the basic elements for quantum information processing. Previous proposals based on photons required non-linear optical elements that allow photons to interact with each other. While such elements have been used for proof-of-principle demonstrations, they have proved too weak to be combined usefully for quantum computation.

Up until now researchers believed that the only feasible option for a photon-based quantum computer was to make the non-linear elements stronger by several orders of magnitude but Emanuel Knill and Raymond Laflamme of Los Alamos and Gerard Milburn of the University of Queensland have proposed a different approach.

Their idea is to use the high sensitivity of single photon detection and exploit the detection results to simulate the effects of non-linear elements. Although this process results in apparently irreversible loss of the ‘quantumnes’ of the system, the researchers have demonstrated that using quantum error correction can prevent this.

The proposed device has several advantages over its rivals. One advantage is that it can work at room temperature, which potentially makes these devices as accessible as personal computers.

It is based on existing technology: beam splitters, phase shifters, single photon sources and detectors. These, however, need to operate at higher precision than currently available.

‘It was widely believed that optics without non-linear elements is no more powerful than currently available, classical computers,’ said Knill. ‘Although the measurements in our scheme irreversibly alter the system, one can still usefully quantum compute. The unwanted effect of measurements can be considered as an error on the system, and as long as both the location and the type of error are known, the system is surprisingly resilient.’