Research work at the University of Cambridge and at Toshiba Research Europe has found that light possessing quantum entanglement can be generated by a simple semiconductor device.

The discovery could lead to long distance, highly secure optical networks, more sensitive medical diagnosis, more powerful computer chips and scalable quantum computing, claimed the researchers.

The managing director of Toshiba’s Cambridge Research Laboratory, Professor Sir Michael Pepper, commented: “In Toshiba we have been convinced for a long time that fundamental physics could be used for a new generation of communication systems that give entirely new functions such as inherent security. The ability to generate entangled photons on demand, by pressing a switch, opens the door to many new applications. These include quantum computers based on novel principles and may even extend to consumer electronics as entangled photons can be used to make devices with much smaller features than normal photons.”

The light source generated by the researchers emits a stream of photons in pairs at regulated times with ‘entangled’, or interrelated, properties.

The new entangled photon source is similar to an ordinary semiconductor light source, but contains a nanometer-sized quantum dot that emits the coupled photons. Toshiba researcher, 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.”

First referred to by Albert Einstein as ‘spooky action at a distance’, measuring one photon appears to alter the property of its entangled twin, even if it is 100s of kilometres away.

Dr Andrew Shields, head of the Quantum Information Group at the Toshiba Laboratory said: “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.”

Another application of entangled photons is in optical imaging. The detail that can be resolved in ordinary images is limited by the wavelength of the light used. Using entangled photons, however, it is possible to produce finer images. This could be useful for very high-resolution microscopy of cell structure in medical diagnosis or to produce finer patterns in the manufacture of ultra-dense computer chips.

The work of the researchers is presented as a paper in Nature.