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Updated: July 8th, 2008 05:26 PM CDT

Toshiba Scientists Find Practical Technology for Entangled Light

M2 PressWIRE
via NewsEdge Corporation


Cambridge - Researchers at Toshiba Research Europe Ltd (TREL) and the Universityof Cambridgehave discovered that light possessing quantum entanglement can be generated by a simple semiconductor device. It could lead to long-distance, highly-secure optical networks safe from hacking, more sensitive medical diagnosis, more powerful computer chips and scalable quantum computing.

Unlike normal light in which the photons (the particles', or quanta, of light) can be regarded as distinct, the new source emits a stream of photons in pairs at regulated times with entangled', or interrelated, properties. The breakthrough will be reported today in the scientific journal Nature.

The new entangled photon source is similar to an ordinary semiconductor light source, but contains a tiny, nanometer-sized quantum dot that emits the coupled photons. TREL researcher and lead author, Dr Mark Stevenson, said: "we discovered that only dots with a certain shape can emit photon pairs which are entangled and that the required shape can be engineered by controlling its growth process."

Entangled photon pairs have the essential attribute that their properties are inter-related. Although measuring either photon in the pair produces a random result, these two seemingly random results are always the same for the two photons of an entangled pair. This means that measuring one photon appears to alter the property of its entangled twin, even if it is 100's of kilometres away. This peculiar feature of quantum theory was referred to by Albert Einstein as spooky action at a distance'.

Dr Andrew Shields, head of the Quantum Information Group at TREL remarks: "Generators of entangled photons are essential components in future IT systems that exploit quantum effects. For example, they could allow us to overcome the current distance limitation in quantum cryptography by teleporting the quantum keys from any location to another. A simple device for generating entangled photons will greatly accelerate these technologies, as well as stimulate new ones. Indeed, analogy with developments after the invention of the semiconductor laser suggests there may be many more applications that we have not yet even imagined."

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