MMIs targeted for quantum computers

Compiled by EuroPhotonics staff

Quantum circuits based on optical multimode interference (MMI) are being used to advance quantum computers.

Building a quantum computer requires a large number of interconnected components, or gates, whose function is similar to that of a microprocessor in a personal computer. The quantum gates of today are large structures that often are too bulky to be scaled to the large, complex circuits required for practical applications.

Now, scientists at the University of Bristol’s Centre for Quantum Photonics have discovered that quantum information can be manipulated with integrated photonic circuits. These circuits are compact – enabling scalability – and stable – with low noise – and soon could be mass-produced for quantum computers.

The team collaborated with a scientist at Imperial College London to show a new class of integrated divides that promises further reduction in the number of components that will be used for building future quantum circuits. The devices, based on optical MMIs, have been widely used in classical optics because of their compact and robust nature, suitable for fabrication tolerance.

Until now, it had not been clear how the devices would work in the quantum regime. The researchers demonstrated that MMIs can perform quantum interference at the high fidelity required. Their findings appeared in the March 1, 2011, issue of Nature Communications (doi: 10. 1038/ ncomms1228).

Scientists now will be able to implement more compact photonic circuits for quantum computing. MMIs can generate large entangled states, at the heart of the exponential speedup promised by quantum computing. The researchers expect that applications will range from new circuits for quantum computation to ultraprecise measurement and secure quantum communication.