The 8-cm-long silica-on-silicon photonic chip in the centre of the picture served as the four-photon boson sampling machine developed by Ian Walmsley and colleagues at Oxford University. For illustrative purposes, a red laser is used to illuminate a portion of the on-chip interferometric network. For the boson sampling experiment, the red laser was replaced with single photon sources. (Courtesy: James C Gates)

‘Boson sampling’ offers shortcut to quantum computing

Jan 8, 2013

With fully fledged quantum computers still potentially decades off, several groups of physicists around the world have found an alternative way of exploiting the processing power of quantum mechanics. They have built a relatively simple photonic device to carry out one specific calculation that is very difficult to perform using classical computers and which, they say, might demonstrate the greater inherent speed of quantum-based devices within the next 10 years.

Quantum computers process quantum bits – or qubits – which can exist in two states at the same time. This could, in principle, lead to an exponential increase in the processing speed of a quantum computer compared with classical devices. This quantum processing could be used, among other things, to rapidly factorize large numbers into their constituent primes and so break codes that are, in practice, uncrackable using conventional computers. However, many technical challenges remain for those trying to develop quantum computers and today the best that a quantum computer can do is to factor small numbers such as 15 and 21.

Some physicists believe that an intermediate quantum computer called a “boson sampling” machine could offer a shortcut to achieving the greater speed of quantum computing. This does not involve what is known as a universal quantum computer, but instead carries out one fixed task. The device consists of a network of beam splitters that converts one set of photons arriving at a number of parallel input ports into a second set leaving via a number of parallel outputs. Its task is to work out the probability that a certain input configuration will lead to a certain output.

Read more: 'Boson sampling' offers shortcut to quantum computing – physics world.

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