Superfast quantum computing, one of the holy grails of science, could be a step closer following the invention of a new device capable of producing so-called “entangled” light on demand. Scientists at Toshiba Corp's research centre in Cambridge, England, said on Wednesday their Entangled Light Emitting Diode (ELED) opened a path to ultra-powerful semiconductor chips. Quantum computers would in theory try out many possible solutions to a problem at once and should solve in seconds problems that take today's fastest machines years to crack. But harnessing the weird powers of quantum physics — which looks at the universe at the level of atoms, photons and other particles — is easier said than done.

Now, though, Andrew Shields of Toshiba and colleagues believe they have a key tool for the job in the form of a simple-to-make device, which can be hooked up to a battery to produce entangled light as and when required. “It's a big step because it means you can now start to integrate lots of devices on a single chip,” Shields said. So far, the Toshiba team haven't got to the stage of doing calculations, but Shields thinks basic quantum computing circuits using the technology could be ready in five years. Quantum computers based on optical processes need a large number of entangled photons, where light particles are linked so that they exist in two possible states simultaneously — something Albert Einstein described as “spooky”. Until now, making entangled light has only been possible using bulky lasers. But Toshiba's new ELED uses standard semiconductor technology and is made of gallium arsenide, a common material in optical electronics. It is similar to conventional light emitting diodes used in consumer electronics and modern household lighting, except it contains a tiny region, called a quantum dot, which converts electrical current into entangled light.

The Toshiba team, working with the University of Cambridge's Cavendish Laboratory, described their invention in a paper in the journal Nature. Other researchers are using atoms or electrons, rather than photons, as quantum computing building blocks. But Shields said the ELED marked a big step forward for the optical approach. Quantum computers are likely to be used initially to solve problems that are otherwise virtually intractable, such as modelling new molecules in pharmaceuticals. Further off, they might also offer an answer when technology based on conventional silicon chips bumps up against the laws of physics and components cannot be made any smaller.

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