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UK scientists unveil nanotechnology for sending single photons through fibre
Researchers at Toshiba Research Europe Ltd (TREL) in Cambridge, in collaboration with the University of Cambridge, 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 team has acheived 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 London.
The world's dimmest fibre source contains a tiny 'quantum dot' of semiconductor, measuring just 45nm in diameter 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.
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.
TREL's work on single photon devices is funded in part by the Department of Trade and Industry/Engineering and Physical Sciences Research Council 'Optical Systems for the Digital Age' and European Commission 'Information Society Technologies' programmes.
Further information: Ward et al, Applied Physics Letters 86, 201111 (2005) http://www.quantum.toshiba.co.uk
Illustration: Image of a layer of quantum dots recorded in an atomic force microscope. Dots similar to the larger, central dot are used to general fibre compatible single photons
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