Boffins shift IT dimensions with photonic quantum computing

This is a representation of a circuit for quantum information processing that makes use of multiport MMI devices. These circuits will be more compact and robust to fabrication tolerances compared to the current 2x2 ports devices.

This is a representation of a circuit for quantum information  processing that makes use of multiport MMI devices. These circuits will be more compact and robust to fabrication tolerances compared to the current 2x2 ports devices.

Boffins at the University of Bristol have made a massive technology breakthrough, by creating compact circuits that could be used to build photonic quantum computers.

The massive advance in computational power could be the catalyst for fundamental changes in society. Experts speculate that it could put time travel, a cure for cancer and an explanation of The Big Society all within reach.

Tremendous advances have been made, said a spokesman for the University of Bristol,  but there is still a long way to go.

Building a quantum computer will require a large number of interconnected components - gates - which work in a similar way to the microprocessors in current personal computers.  Currently, most quantum gates are large structures and the bulky nature of these devices prevents scalability to the large and complex circuits required for practical applications.

Recently, the researchers from the University of Bristol's Centre for Quantum Photonics showed, in several important breakthroughs, that quantum information can be manipulated with integrated photonic circuits. Such circuits are compact (enabling scalability) and stable (with low noise) and could lead in the near future to mass production of chips for quantum computers.

Along with Dr Terry Rudolph at Imperial College, London the team discovered a new class of integrated divides that could slash the number of components needed to build future quantum circuits.

These devices, based on optical multimode interference (MMIs) have been widely employed in classical optics as they are compact and very robust to fabrication tolerances.  "While building a complex quantum network requires a large number of basic components, MMIs can often enable the implementation with much fewer resources," said Alberto Peruzzo, PhD student working on the experiment.

Until now it was unclear how these devices would work in the quantum regime.  Bristol researchers say they have proved that MMIs can perform quantum interference at the high fidelity required.

Scientists will now be able to implement more compact photonics circuits for quantum computing.  MMIs can generate large entangled states, at the heart of the exponential speedup promised by quantum computing.

"Applications will range from new circuits for quantum computation to ultra precise measurement and secure quantum communication," said Professor Jeremy O'Brien, director of the Centre for Quantum Photonics.

The team now plans to build new sophisticated circuits for quantum computation and quantum metrology using MMI devices.
This was last published in March 2011

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