Many groups of research scientists around the world are trying to build a quantum computer to run algorithms that take advantage of the strange effects of quantum mechanics such as entanglement and superposition.  A quantum computer could solve problems in chemistry by simulating many body quantum systems, or break modern cryptographic schemes by quickly factorising large numbers.

Previous research shows that if a quantum algorithm is to offer an exponential speed-up over classical computing, there must be a large entangled state at some point in the computation and it was widely believed that this translates into requiring a single large device.

In a paper published today in Proceedings of the Royal Society A, Dr Steve Brierley of Bristol's School of Mathematics and colleagues  show that, in fact, this is not the case.  A network of small quantum computers can implement any quantum algorithm with a small overhead.

The key breakthrough was learning how to efficiently move quantum data between the many sites without causing a collision or destroying the delicate superposition needed in the computation.  This allows the different sites to communicate with each other during the computation in much the same way a parallel classical computer would do.

Dr Brierley said: "Building a computer whose operation is based on the laws of quantum mechanics is a daunting challenge.  At least now we know that we can build one as a network of small modules."

Paper

'Efficient Distributed Quantum Computing' by Robert Beals, Stephen Brierley, Oliver Gray, Aram W. Harrow, Samuel Kutin, Noah Linden, Dan Shepherd and Mark Stather in Proceedings of the Royal Society A