Scientists Develop Chip For Quantum Computer

A new type of silicon chip that utilises light instead of electricity to pass information could pave the way for the first quantum supercomputer within the next ten years.

British scientists have developed the photonic chip that could lead to ultra powerful ‘quantum’ computers, capable of conducting much more complex calculations than current computers, in just a fraction of the time.

The photonic chip was built by an international research group that was led by scientists from the University of Bristol’s Centre for Quantum Photonics. They developed a silicon chip that is capable of performing complex calculations and simulations using quantum particles or quantum bits (qubits) rather than the conventional bits used in today’s computers.

Qubit, Not Bits

Conventional bits or transistors can be in one of only two states at any one time (1 or 0). However, a qubit is kept in a state where it consists of a superposition of all possible states at the same time. As long as the qubit is kept form interaction with the rest of the world, quantum mechanics states that all possible states exist, so a quantum computer could theoretically process all possible input values for a function at the same time.

A quantum computer could therefore calculate answers to optimisation problems, much more quickly, trying all possible solutions at the same time, instead of going through them by trial and error.

“It is widely believed that a quantum computer will not become a reality for at least another 25 years,” said Professor Jeremy O’Brien, Director of the Centre for Quantum Photonics. “However, we believe, using our new technique, a quantum computer could, in less than ten years, be performing calculations that are outside the capabilities of conventional computers.”

The Bristol boffins desscribed how they have developed a technique that uses two identical particles of light (photons) moving along a network of circuits in a silicon chip in order to perform an experiment known as a quantum walk. They admit that quantum walk experiments using one photon have been done before and can even be modelled exactly by classical wave physics. However, this is the first time a quantum walk has been performed with two particles and they feel that the implications are “far-reaching.”

“Using a two-photon system, we can perform calculations that are exponentially more complex than before,” said Prof O’Brien. “This is very much the beginning of a new field in quantum information science and will pave the way to quantum computers that will help us understand the most complex scientific problems.”

But the scientists stressed that it will be a long development before quantum computing arrives, with the team expected to apply their new results immediately for developing new simulation tools in their own lab. In the long term however, “a quantum computer based on a multi-photon quantum walk could be used to simulate processes which themselves are governed by quantum mechanics, such as superconductivity and photosynthesis,” they said.

“Our technique could improve our understanding of such important processes and help, for example, in the development of more efficient solar cells,” adds Prof O’Brien.

Other applications include the development of ultra-fast and efficient search engines, designing high-tech materials and new pharmaceuticals.

Two Photon Advance

The scientists were also keen to make the point that the leap from using one photon to two photons is not trivial because the two particles need to be identical in every way and because of the way these particles interfere, or interact, with each other. There is no direct analogue of this interaction outside of quantum physics.

“Now that we can directly realise and observe two-photon quantum walks, the move to a three-photon, or multi-photon, device is relatively straightforward, but the results will be just as exciting” says Prof O’Brien. “Each time we add a photon, the complexity of the problem we are able to solve increases exponentially, so if a one-photon quantum walk has 10 outcomes, a two-photon system can give 100 outcomes and a three-photon system 1000 solutions and so on.”

The scientists included researchers from Tohoku University (Japan), the Weizmann Institute (Israel) and the University of Twente (the Netherlands).