Nanotechnology alight' breakthrough

Paul Boughton

Researchers at Toshiba Research Europe Ltd (TREL) in Cambridge, UK, have announced that they have developed a light source that can be used to send single photons in a regular stream through optical fibre over long distances.

The device is needed for future quantum networks exploiting the particle-like properties of light. The results were announced at the prestigious Quantum Electronics and Laser Science (QELS) Conference in Baltimore.

The team has achieved the breakthrough by developing a semiconductor nanotechnology tailored for use with ordinary telecom fibre cables. It results from an initiative funded by the Department of Trade and Industry involving TREL, University of Cambridge and Imperial College.

The world's dimmest fibre source contains a tiny aquantum dot' of semiconductor, measuring just 45nm in radius and 10nm in height, which emits photons (the particles of light) one at a time. By manipulating the way in which the dot was formed, the emitted photons were tuned to a wavelength that allows long distance propagation in ordinary fibre optic cables.

Dr Andrew Shields, head of the Quantum Information Group at TREL comments: "Exploiting the quantum properties of light allows us to communicate and process information in ways that have not been possible previously. A good example is in quantum cryptography, which allows us to verify the secrecy of information sent on single photons. These developments show that single photon sources can now be applied to real communication systems," he added.

Quantum Information Technology concerns the transport and processing of information using individual particles such as electrons or photons. Using single particles in this way brings unexpected advantages. By sending information encoded upon single photons (the particles of light) it is possible to test the secrecy of each communication.

Professor Will Stewart, Chairman of Innos, late Chief Scientist at Marconi and who monitors progress in the project for DTI, adds: "Quantum is nature's digital information system -- and the natural goal for our own digital systems. The team is to be congratulated on making a significant step along this road."

Single photon sources are needed for future applications in quantum information technology, such as quantum cryptography, a technique to distribute secret digital keys on a fibre-optic network.

Here a single-photon source is required to improve the security and bit rate of current systems, which rely on strongly attenuated lasers to simulate single photon pulses.

TREL, who have already developed a robust system for quantum key distribution, confirmed that the performance of the developed single photon source is sufficient for real applications and plan to integrate the device in their system within the next year.

TRELs work on single photon devices is funded in part by the Department of Trade and Industry/Engineering and Physical Sciences Research Council aOptical Systems for the Digital Age' and European Commission aInformation Society Technologies' programmes.

Ian Williams, Programme Manager for the DTI's LINK Optical Systems Programme, said: "This is a most impressive achievement from one of the most ambitious and technically challenging projects we supported under the LINK Optical Systems Programme. This advance now offers the prospect of great improvements in IT security with potential benefits to IT users worldwide."

For more information, visit www.toshiba-europe.com/research

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